Solid State Drives - Seminar Report for Semester 6 Computer Engineering - VIT,UoM

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This report is intended as a guide to emerging solid state storage technology, in particular, to the introduction of solid state drives.
Adding a solid-state drive (SSD) to your computer is simply the best upgrade at your disposal, capable of speeding up your computer in ways you hadn't thought possible. But as with any new technology, there's plenty to learn.
The consumer is no longer limited to just accepting pre-configured systems and, even when purchasing a system, should have an avenue to understand what purpose the storage device within serves as well as how it does what it does.
A solid-state drive (SSD) is a data storage device for your computer.
In everyday use, it provides the same functionality as a traditional hard disk drive (HDD)—the standard for computer storage for many years.

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Solid State Drives - Seminar Report for Semester 6 Computer Engineering - VIT,UoM

  1. 1. 1 SEMINAR REPORT on Solid State Drives (SSDs) SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BACHELOR OF ENGINEERING AT SEMESTER 6 in COMPUTER ENGINEERING by RB UNDER THE GUIDANCE OF Prof. Sachin Bojewar VIDYALANKAR INSTITUTE OF TECHNOLOGY DEPARTMENT OF COMPUTER ENGINEERING VIDYALANKAR INSTITUTE OF TECHNOLOGY UNIVERSITY OF MUMBAI 2013-14
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  3. 3. 3 VIDYALANKAR INSTITUTE OF TECHNOLOGY DEPARTMENT OF COMPUTER ENGINEERING CERTIFICATE This is to certify that Mr RB has satisfactorily completed seminar work entitled “Solid State Drives (SSDs)”. ---------------------------------- ---------------------------- Prof. Sachin Bojewar Head of Computer Engineering Internal Examiner External Examiner
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  5. 5. 5 Abstract This report is intended as a guide to emerging solid state storage technology, in particular, to the introduction of solid state drives. Adding a solid-state drive (SSD) to your computer is simply the best upgrade at your disposal, capable of speeding up your computer in ways you hadn't thought possible. But as with any new technology, there's plenty to learn. The consumer is no longer limited to just accepting pre-configured systems and, even when purchasing a system, should have an avenue to understand what purpose the storage device within serves as well as how it does what it does. A solid-state drive (SSD) is a data storage device for your computer. In everyday use, it provides the same functionality as a traditional hard disk drive (HDD)—the standard for computer storage for many years.
  6. 6. 6 TABLE OF CONTENTS Sr No. Topic Page No. 1. Introduction (Brief description) 8 2. Review Of Literature 10 3. Topic and its detailed Description 12 4. Applications 47 5. Conclusion 53 References 56
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  8. 8. 8 Introduction Solid state is term that refers to electronic circuitry that is built entirely out of semiconductors. The term was originally used to define those electronics such as a transistor radio that used semiconductors rather than vacuum tubes in its construction. Most all electronics that we have today are built around semiconductors and chips. In terms of a SSD, it refers to the fact that the primary storage medium is through semiconductors rather than a magnetic media such as a hard drive. In fact, you wouldn't even know whether you're using an SSD or HDD if it wasn't for the differences in how they operate. HDDs store their data on spinning metal platters, and whenever your computer wants to access some of that data a little needle-like component (called the "head") moves to the data's position and provides it to the computer. Writing data to a HDD works in a similar fashion, where parts are constantly moving. SSDs, on the other hand, don't move at all. This is a simplified explanation, of course, but you might have noticed that the SSD's process seems a bit more direct and efficient. It is, and speed is the primary advantage of an SSD over a traditional HDD. This makes an SSD the single best upgrade for your computer if you're looking for a way to make it operate faster.
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  10. 10. 10 Review of Literature In 1956, IBM shipped the world's first hard disk drive, or HDD, in the RAMAC 305 system. The drive used 50 24-inch (61-centimeter) platters, stored a meager 5 megabytes of data and took up more room than two refrigerators. It used to cost $50,000 ($421,147 in 2012). Since then, hard drives have grown smaller, more capacious and become less expensive. For example, the Seagate Momentus laptop hard drive, with a form factor of just 2.5 inches (6.4 centimeters), offers 750 gigabytes of storage for less than $100. But even with advanced protection technologies, the Momentus drive, like all HDDs, can crash and burn, taking precious data with it. That's because hard drives have mechanical parts that can fail. Drop a laptop, and the read-write heads can touch the spinning platters. This almost always results in severe data loss. Most users are familiar with flash memory from its use in consumer electronics products, including digital cameras, MP3 players, and USB flash drives. By combining flash memory with advanced controller technology, the industry has, over the past several years, been developing a new storage device based on flash memory―the solid state drive (SSD). Solid state drives interface with the host system using the same protocols as disk drives, but SSDs store and retrieve file data in flash memory arrays rather than on spinning media. Continuing advances in both flash memory and controller technology are, for the first time, enabling solid state drive designs that begin to meet the capacity, performance, and reliability requirements for use in personal as well as server environments.
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  12. 12. 12 Topic and its Detailed Description HISTORY The PC hard drive form factor standardized in the early 1980s with the desktop-class 5.25-inch form factor, with 3.5-inch desktop and 2.5-inch notebook-class drives coming soon thereafter. The internal cable interface has changed from Serial to IDE to SCSI to SATA over the years, but it essentially does the same thing: connects the hard drive to the PC's motherboard so your data can be processed. Today's 2.5- and 3.5-inch drives use SATA interfaces almost exclusively (at least on most PCs and Macs). Capacities have grown from multiple megabytes to multiple terabytes, an increase of millions fold. Current 3.5-inch HDDs max out at 6TB, with 2.5-inch drives at 4TB max. The first primary drives that we know as SSDs started during the rise of netbooks in the late 2000s. In 2007, the OLPC XO-1 used a 1GB SSD, and the Asus Eee PC 700 series used a 2GB SSD as primary storage. The SSD chips on low-end Eee PC units and the XO-1 were permanently soldered to the motherboard. As netbooks, ultrabooks, and other ultraportables became more capable, the SSD capacities rose, and eventually standardized on the 2.5-inch notebook form factor. This way, you could pop a 2.5-inch hard drive out of your laptop or desktop and replace it easily with an SSD. Other form factors emerged, like the mSATA miniPCI SSD card and the DIMM-like SSDs in the Apple MacBook Air, but today many SSDs are built into the 2.5-inch form factor. The 2.5-inch SSD capacity tops out at 1TB currently, but will undoubtedly grow as time goes by. DIFFERENCE BETWEEN MEMORY AND STORAGE In computer lingo, there's a difference between memory and storage. Random-access memory, or RAM (or simply memory), holds the program a computer is executing, as well as any data. Like a person's short-term memory, RAM is fleeting and requires power to do its job. Storage, on the other hand, holds all your digital life -- apps, files, photos and music. It retains that stuff even if the power is switched off. Both RAM and storage boast their capacity based on the number of bytes they can hold. For a modern computer, RAM typically comes in 4, 6 or 8 gigabytes. Storage can have almost 100 times more capacity -- the hard drive of a typical laptop, for example, can hold 500 gigabytes.
  13. 13. 13 Here's where it gets a little sticky. Some storage devices have what's referred to as flash memory, a confusing term that blurs the line between RAM and storage. Devices with flash memory still hold lots of info, and they do it whether the power's on or not. But unlike hard drives, which contain spinning platters and turntable-like arms bearing read-write heads, flash-memory devices have no mechanical parts. They're built from transistors and other components you'd find on a computer chip. As a result, they enjoy a label -- solid state -- reserved for devices that take advantage of semiconductor properties. TYPES OF FLASH MEMORY There are two types of flash memory, NAND and NOR. The names refer to the type of logic gate used in each memory cell. (Logic gates are a fundamental building block of digital circuits). Both contain cells -- transistors -- in a grid, but the wiring between the cells differs. In NOR flash, the cells are wired in parallel. In NAND flash, the cells are wired in a series. Because NOR cells contain more wires, they're bigger and more complex. NAND cells require fewer wires and can be packed on a chip in greater density. As a result, NAND flash is less expensive, and it can read and write data much more rapidly. This makes NAND flash an ideal storage technology and explains why it's the predominant type of memory in solid-state drives. NOR flash is ideal for lower- density, high-speed, read-only applications, such as those in code-storage applications. Armed with this information, we can offer a more precise definition of a solid-state drive: It's a device that uses NAND flash to provide non-volatile, rewritable memory. In computers, a solid-state drive can be used as a storage device, replacing the traditional hard disk drive. In fact, manufacturers produce SSDs with shapes and footprints that resemble HDDs so the two technologies can be used interchangeably. But that's where the similarities end.
  14. 14. 14 Basic Terms Related to SSDs
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  17. 17. 17 BASIC COMPONENTS IN AN SSD SSDs are comprised of a few different main components:  SSD Controllers: Every SSD includes a controller, just as does a HDD, that incorporates the electronics that bridge the NAND memory components to the host computer. The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance. There are numerous circuits and programming required for the operation of the device. Some of the functions performed by the controller include encryption and compressing data before it is written to the drive as well as: Read And Write Disturbs - The act of reading from or writing to a cell can cause adjacent cells to change state. This is known as bit-flop and has to be monitored for each read and write. Error Correcting Code (ECC) - Used to insure that data read, written or stored has not been unintentionally altered. Invalid Block Management - Blocks that contain cells that are not capable of properly storing data must be mapped out of the user accessible memory range before data is stored. The blocks also need to be tracked for the life of the drive. Power data protection - Needed to guard against the involuntary program/erase of cells during power transitions. Garbage Collection - Optimize free space to reduce erase before program operations. Wear Leveling - Blocks are monitored for the number of write cycles that have been performed. The blocks are reused in an ascending order starting with the blocks that have gone through the fewest write cycles.
  18. 18. 18 Some common SSD controller developers include: o Samsung o Marvell o SandForce (Now owned by LSI) - SandForce controllers are the only devices with a compression algorithm in real time. Basic, it minimizes the impact of specific submissions on the Flash. o Toshiba o Indilinx (owned by OCZ.) o Intel o JMicron  Memory: Most SSDs use NAND flash memory because of the lower cost compared to DRAM. Flash memory SSDs are slower than DRAM SSDs which are mostly used in enterprise applications and not available to the consumer market. NAND Flash Memory - NAND flash memory is a type of non-volatile storage technology that does not require power to retain data. This is the equivalent of a HDD's platters. NOR flash was first introduced by Intel in 1988. NAND flash was introduced by Toshiba in 1989. The two chips work differently. NAND has significantly higher storage capacity than NOR. NAND flash has found a market in devices to which large files are frequently uploaded and replaced. MP3 players, digital cameras and USB drives use NAND flash. NOR flash is faster, but it's also more expensive. NOR is most often used in mobile phones. An important goal of NAND flash development has been to reduce the cost per bit and increase maximum chip capacity so that flash memory can compete with magnetic storage devices like hard disks. New developments in NAND flash memory technology are making the chips smaller, increasing the maximum read-write cycles and lowering voltage demands. 0's and 1s: Tunneling is used to alter the placement of electrons in the floating gate. An electrical charge is applied to the floating gate. The charge enters the floating gate and drains to a ground. This charge causes the floating-gate transistor to act like an electron gun. The excited electrons are pushed through and trapped on other side of the thin oxide layer, giving it a negative charge.
  19. 19. 19 These negatively charged electrons act as a barrier between the control gate and the floating gate. A special device called a cell sensor monitors the level of the charge passing through the floating gate. NAND flash memory uses floating gate MOSFET transistors. Their default state is when the charge is over the 50%. If the flow through the gate is above the 50% threshold, it has a value of 1. When the charge passing through drops below the 50% threshold, the value changes to 0. 0's are data, 1's is erase - the fundamental laws of MLC NAND dictate this. You only write the 0's when you write data to NAND. So in an erased state the NAND has to report a 1. Lower priced drives usually use multi-level cell NAND. MLC NAND is what is in almost all consumer SSDs. Higher priced SSDs usually use single-level cell NAND; these drives are usually used for enterprise applications due to better durability. SLC NAND cost about 3 times as much as a MLC NAND. Single-level Cell (SLC) NAND - SLC NAND can store only one data bit per NAND flash cell. This leads to faster transfer speeds, higher cell endurance, and lower power consumption. The downside to SLC chips used in SSDs is the manufacturing cost per megabyte and total capacity which is less per NAND cell than MLC. SLCs are intended for the high-end consumer and server market and they have approximately 10 times more endurance compared to MLC. Multi-level Cell (MLC) NAND - MLC NAND stores two bits per NAND flash cell. Storing more bits per cell achieves a higher capacity and lower manufacturing cost per megabyte. MLC SSDs are designed for the mainstream consumer market and are much faster compared to standard hard disk drives. MLC SSDs are improving with faster and more efficient technologies and are being adopted into the high-end consumer and server markets. Endurance Multi-level Cell (eMLC) NAND - eMLC NAND is basically more expensive MLC flash with better endurance. Triple Level Cell (TLC) NAND - TLC NAND stores three bits per cell. However P/E cycles for TLC NAND is significantly lower than that of MLC NAND.
  20. 20. 20 Now out of the types of NAND (SLC, eMLC, and MLC) you can get NAND that operate at different speeds. The communication bus between the flash and the controller is also important, it can be either asynchronous, synchronous, or Toshiba, SanDisk, and Samsung's NAND, similar to the synchronous, Toggle-Mode DDR. This is important when determining the SSD you want. Toggle-Mode DDR and Synchronous NAND are preferred over much slower Asynchronous NAND. Toggle-Mode DDR and Synchronous NAND fare far better than Asynchronous NAND with compressed data. Synchronous - Faster, more expensive . Asynchronous - Slower, less expensive . The performance of the SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow compared to when when multiple NAND chips that operate in parallel. The bandwidth scales and the high latencies can be usually be hidden. Micron and Intel initially made faster SSDs by implementing data striping (similar to RAID 0) and interleaving in their architecture. This enabled the creation of SSDs with 250 MB/s effective read/write speeds with the SATA 3 Gb/s interface in 2009. Two years later and continuing to leverage this parallel flash connectivity, SandForce released consumer-grade SATA 6 Gb/s SSD controllers which support 500 MB/s read/write speeds. NAND manufactures include: o Micron Technology, Inc. o Intel Corporation o Hynix Semiconductor o Phison Electronics Corp. o SanDisk Corporation o Toshiba o Samsung o Sony Corporation o Spansion
  21. 21. 21 Some NAND groups include: o ONFi (Open NAND Flash Interface) Working Group o IMFT (Intel Micron Flash Technologies) o Flash Forward (Sandisk and Toshiba)  Cache or Buffer: A flash-based SSD typically uses a small amount of DRAM as a cache, similar to the cache in hard disk drives. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. Data is not permanently stored in the cache. SandForce does not use an external DRAM cache on their designs, but still achieve very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.  Battery or super capacitor: Another component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed. In the case of MLC flash memory, a problem called lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.  Host Interface The host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller. The interface is generally one of the interfaces found in HDDs. Types include: o Serial ATA o M.2 (NGFF) o Serial Attached SCSI (SAS) o Fibre Channel o PCI Express
  22. 22. 22 We are going to understand a description of SSD components along with an understanding of the purpose of each. The purpose would be to provide a solid foundation in your understanding of SSDs, but also, will also help in your final decision and choice of the right SSD for the job. Every SSD has a number of components that are always present. There are different SSD form factors which we will cover later but, for the most part, there is always a printed circuit board (PCB) which contains an interface to connect to the computer, SSD controller and a number of modules of NAND flash memory chips. Here is the OWC Mercury Electra 6G SSD for this understanding because it is a 2.5″ typical notebook formfactor and the most common that most likely see today. SATA INTERFACE The SATA interface is best seen in the left photo above and consists of a gold connector which easily connects to your laptop or desktop computer. Without belaboring on the definition and revisions of SATA, the consumer only really needs to understand that all SATA SSDs are backward and forward compatible and any will serve the purpose it is intended without question. Most computer systems in use are SATA 2 with newer systems now released with SATA 3 capability.
  23. 23. 23 The difference between the two breaks down to how fast the data can be transferred from the SSD to your computer and, in the case of applications, executed. Typically, a SATA 2 SSD will only transfer speeds as fast as 280 megabytes per second (MB/s) whereas new SATA 3 drives are reaching as high as 550MB/s in a single form factor notebook or desktop SATA 3 SSD. Lets take a look at two typical benchmarks, the one on the left depicting the Sandisk Ultra SATA 2 SSD performance with the one on the right depicting the Corsair Force Series GT SATA 3 SSD. We can see that these are not peak results, this being the fault of the benchmark software for the most part. An important observation, however, is that SATA 3 typically doubles the performance of SATA 2. SSD PROCESSOR OR CONTROLLER The SSD processor (or controller is it is more commonly referred to) is the heart and soul of the SSD. It is the engine by which information is pulled from storage, translated and then sent to the SATA interface for travel to your computer system. It is the sole reason that a typical SSD is 5-6 times faster than a hard drive in data travel and also the reason that we see a starting point of about a 90x increase in the information retrieval (disk access) from an SSD as compared to that of a hard drive.
  24. 24. 24 Unlike a hard drive which has only one route of information retrieval, the typical SSD can have as many as eight routes of travel or ‘channels’ as they are more commonly referred to. So, if you can again refer back to the OWC SSD above you will note that their are 16 NAND flash memory chips that are used for storage. This would mean that every two has its own channel ‘or highway’ by which to send and receive information. PROCESSOR TYPES In today’s SSD environment there are two common processors which differ in their means of storage. The first utilizes compression to store data, debatably the most popular and a company named SandForce (recently purchased by LSI) is the only that has perfected it. In observing performance benchmarks, a SandForce SSD can be easily identified as it is able to achieve almost equal read and write transfer speeds where others cannot do this. This is only possible because SandForce has been able to achieve a 1 to .6 write ratio which allows for almost equal read and write performance.
  25. 25. 25 You will notice that the high sequential read and write scores are much closer with the ‘SandForce Driven’ OCZ Vertex SATA 3 SSD on the left as compared to the Intel 510 SATA 3 SSD on the right. The other family of processors are those that do not use compression and are common in processors manufactured by Marvell, Intel, Samsung, and some lesser known names such as JMicron and Phison. The below picture is of a Crucial M4 512GB SATA 3 SSD which utilizes the Marvell 9174 controller.
  26. 26. 26 Marvell processors have gained most of their success through Crucial/Micron although Intel, Corsair, and many other manufacturers have relied in them as well. In the Crucial 512GB we see above, there are 16 memory modules of 32GB capacity each for a total of 512GB. Typically, all SSDs are normally advertised in capacities that directly reflect the memory module itself which traditionally is a power of 4. A single module could have been as low as 4GB where now they can reach 64GB. This is why we would normally see 32, 64, 128, 256, 512GB SSDs advertised although manufacturers such as Intel have ventured off the beaten path to advertise capacities of 320GB. SYNCHRONOUS VERSUS ASYNCHRONOUS NAND FLASH MEMORY In the past few months, another chapter has been added to SSD selection which has to do specifically with memory. Whereas the original run of SSDs were being released with synchronous or toggle mode NAND flash modules, SSDs have now been introduced with asynchronous NAND flash memory. Many SSDs with synchronous or toggle mode memory are now being marketed with words such as ‘Premium’ or ‘Enthusiast Edition’. The difference between the two is very simple. SSDs that utilize premium memory are more expensive and perform better when transferring incompressible files such as music, photos and video. Conversely, SSDs that utilize asynchronous NAND flash memory offer less performance ‘on paper’ however are less demanding on the pocket book. The typical consumer, and even the experts, cannot tell the difference between the two in every day use. The less expensive SSD with ‘async’ memory is meant for the everyday typical user whereas the more expensive premium SSD is meant for photographers, videographers and those involved in the music industry.
  27. 27. 27 SSD Types and Form Factors NOTEBOOK 2.5″ SSDs The 2.5″ SSD is the most popular size solid state drive and will fit into just about any consumer PC, given exception new ultrabook designs which are just too thin to house anything but a mSATA SSD as it is only as think as a 25 cent piece. Notebook SSDs have become so popular, in fact, that most manufacturers don’t even sell the larger and much heavier 3.5″ desktop size, choosing instead to include a 2.5″ to 3.5″ adapter with their notebook SSD kits. Below is the Kingston HyperX 240GB SSD. The notebook SSD is available in either SATA 2 or SATA 3 which means that performance speeds as high as 285MB/s (SATA 2) and 550MB/s (SATA 3) are possible IF you have a system that supports the appropriate interface. It is an important to consider that buying a SATA 3 SSD serves no purpose if your laptop (or desktop) only supports SATA 2 as 95% of those on the market presently do.
  28. 28. 28 The Kingston HyperX SSD PCB (printed circuit board) does a very good job of displaying the SATA 3 interface on the left, SandForce SF-2281 SATA 3 processor as well as eight of the 16 modules of NAND flash memory which provide storage for this SSD. SUPER SLIM 2.5″ SSD DESIGN The normal consumer SSD available today has dimensions of approximately 69mm wide x 100mm long x 9.5mm thick.One of the first solid state drives released, the Intel X25m, was actually a superslim SSD and they have recently followed suit with the Intel 320 Series SSD, both of which are only 7mm thick with a black adapter that allows their fit in typical notebooks.
  29. 29. 29 MSATA SSDS The mSATA SSD measures about 50mm long x 30mm wide x 4.85mm thick, or 1/3 the size of a business card. The size of this SSD is key to its present surge into the ultrabook market. mSATA SSDs are now being found in ultrabooks such as the Samsung Series 9 and Toshiba Z830 that we have reviewed as well as some larger notebooks manufactured by Dell. They use a modified mPCIe (mini PCI express) interface and are typically SATA 2 although we are now seeing SATA 3 entries by Runcore, Samsung and AData.
  30. 30. 30 PCIE SSDS PCIe SSDs are the workhorse of the bunch as a result of the absolutely amazing speeds they can achieve. PCIe SSD can be had for less than $700 and reaches performance speeds as high as 1.5GB/s. To date, consumer PCIe cards have been the exclusive release of OCZ and the reason that they can reach such high speeds is actually pretty interesting and demonstrates just how fast technology is moving forward. Here we are just moving into SATA 3 which technically doubles the speed of SATA 2 systems and along comes PCIe SSDs which sail by SATA speeds with ease. This is because PCIe SSDs clip into your motherboards PCIe 2.0 slot and are not subject to the bottlenecks seen in SATA SSDs. The downfall, of course, is that these are limited only to computer systems with an available PCIe slot, however, the absolute speeds reached are incredible.
  31. 31. 31 DUAL DRIVES SYSTEMS, HYBRID AND DISK CACHING As much of a benefit as hard drive capacity is, it is simply a killer in performance. As incredible as SSD performance is, higher capacity necessitates a higher price. The key to this will definitely be the combination of both at a price the consumer is willing to pay. RevoDrive Hybrid PCIe SSD : Revo 3 SSD coupled with the 1TB capacity of the hard drive. Disk caching is simply the retention of ‘hot’ programs and data within the SSD cache while those files seldom used remain on the hard drive. The advantage here is the fact that the frequently used data is learned, remembered and remains in the cache even after the computer has been shut down. This is the beauty behind 17 second start ups and faster performance with a cached drive in comparison to those minute plus start ups we see in a typicle system. For the desktop, disk caching certainly improves on the suggestion of purchasing a moderate size SSD for a boot drive and hard drive for storage of larger media to include video, music and pictures. For the notebook however, we have to look at options available to meet our needs. This might mean a higher priced SSD, or purchase of a system with dual drive bays or a mSATA and HDD bay, or, we have seen many swap out their DVD drive for a hard drive and adapter in the past.
  32. 32. 32 How Solid-state Drives Save Data On the outside, solid-state drives look just like HDDs. They're rectangular in shape, covered in a brushed-metal shell and sized to match industry-standard form factors for hard drives -- typically 2.5 and 3.5 inches (6.4 and 8.9 centimeters). But beneath the silver exterior, you'll find an array of chips organized on a board, with no magnetic or optical media in sight. Much of that stuff could fit into a smaller space, but SSD manufacturers dress up their components in extra "housing" to make sure they fit into existing drive slots of laptops and desktop PCs. How a Traditional HD Stores Data : Compared to the stark simplicity of a solid-state drive, the innards of a hard drive are a marvel of motion, sound and activity. Round platters, arranged on a spindle, can spin at 7,200 revolutions per minute. An actuator arm, branching into multiple read-write heads, races across the platters in too-fast-to-be-seen bursts of speed. The arm connects to the actuator block, which holds the instructions for moving the read-write heads. As those instructions are called up, sometimes up to 50 times a second, the arm pivots at one end and moves the heads in unison over the platters. Once a head arrives at a certain location on a platter, an electromagnet produces a magnetic field, which aligns data-carrying domains in the underlying track. Each domain can be aligned in one of two possible directions -- 1 or 0. As these alignments change, they form patterns that correspond to discrete chunks of digital information. How NAND stores data : The NAND flash of a solid-state drive stores data differently. Recall that NAND flash has transistors arranged in a grid with columns and rows. If a chain of transistors conducts current, it has the value of 1. If it doesn't conduct current, it's 0. At first, all transistors are set to 1. But when a save operation begins, current is blocked to some transistors, turning them to 0. This occurs because of how transistors are arranged. At each intersection of column and row, two transistors form a cell. One of the transistors is known as a control gate, the other as a floating gate. When current reaches the control gate, electrons flow onto the floating gate, creating a net positive charge that interrupts current flow. By applying precise voltages to the transistors, a unique pattern of 1s and 0s emerges. NAND flash comes in two flavors based on how many 1s and 0s can be stored in each cell. Single-level cell (SLC) NAND stores one bit -- either a 1 or a 0 -- per cell. Multi-level cell (MLC) NAND stores two bits per cell. MLC flash delivers higher capacity, but it wears out more quickly (yes, wears out -- we'll cover that more in a couple of pages). Still, it's less expensive per gigabyte than SLC and, as a result, is the preferred technology in almost all consumer-level SSDs.
  33. 33. 33 MAINTENANCE OF AN SSD Basically they maintain themselves, there are many things that SSD manufactures do to make sure the drive lasts like over provisioning, having garbage collection, and wear leveling built into the drive. Let’s talk about the main points of what an SSD does to maintain itself. In a nutshell, all SSDs have garbage collection. TRIM simply optimizes it. It is not needed, but preferred to have enabled as it reduces write amplification and speeds up garbage collection. Garbage collection (GC) is a fundamental process with all solid state drives (SSDs), but it can be implemented in different ways that can impact the overall SSD performance and endurance. We look at how GC works, how it can be implemented, and how it relates to the TRIM command and over provisioning. Unlike hard disk drives (HDDs), NAND flash memory cannot overwrite existing data they must first erase old data before writing new data to the same location. With SSDs, GC is the name for the process of relocating existing data to new locations and allowing the surrounding invalid data to be erased. Flash memory is divided into blocks, which is further divided in pages. Data can be written directly into an empty page, but only whole blocks can be erased. Therefore, to reclaim the space taken up by invalid data, all the valid data from one block must be first copied and written into the empty pages of a new block. Only then can the invalid data in the original block be erased, making it ready for new valid data to be written. OS AWARENESS VS DRIVE AWARENESS In an HDD system, the Operating System (OS) can simply request that new data be written to the same location where the older, now invalid data, is stored, and the HDD will directly overwrite the old data. In an SSD, however, the page must first be erased before it can be written to locations previously holding data the SSD cannot directly overwrite existing data as stated earlier. The OS understands the files, their structure, and the logical locations where they are stored, but does not understand the physical storage structure of the storage device. In any storage system, the storage device doesn’t know the file structure it simply knows that there are bytes of data written in specific sectors. The storage system, whether SSD or HDD, returns the data from physical locations when the OS asks for data in the corresponding logical locations. When the OS deletes the file, it simply marks the space used for that data as free in its logical data table. With HDDs, the OS does not need to tell the storage device anything about the deletion because it would simply write something new into that same physical location in the future.
  34. 34. 34 In the case of an SSD, it only becomes aware that the data is deleted (or invalid) when the OS tries to write to that location again. At that time the SSD marks the old data as invalid and it writes the new data to a new physical location. It may also perform GC at that same time, but that varies between SSD architectures and other conditions at that moment. THE TRIM COMMAND In computing, a TRIM command allows an operating system to inform a solid-state drive (SSD) which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name. TRIM was introduced soon after SSDs started to become an affordable alternative to traditional hard disks. Because low-level operation of SSDs differs significantly from traditional hard disks the typical way in which operating systems handle operations like deletes and formats (not explicitly communicating the involved blocks/pages to the underlying storage medium) resulted in unanticipated progressive performance degradation of write operations on SSDs. The advantage of the TRIM command is that it enables the SSD’s GC to skip the invalid data rather than moving it, thus saving time not rewriting the invalid data. This results in a reduction of the number of erase cycles on the flash memory and enables higher performance during writes. The SSD doesn’t need to immediately delete or garbage collect these locations it just marks them as no longer valid. TRIM can be initiated in Windows by actions such as emptying the Recycle Bin, but the SSD must also execute the command. OSes that support TRIM include:  Win 8/8.1  Win 7  Linux distros since 2010  Mac OSX lion
  35. 35. 35 Over-provisioning: Over-provisioning (sometimes spelled as OP, over provisioning, or overprovisioning) is the difference between the physical capacity of the flash memory and the logical capacity presented through the operating system (OS) as available for the user. During the garbage collection, wear-leveling, and bad block mapping operations on the SSD, the additional space from over-provisioning helps lower the write amplification when the controller writes to the flash memory. When an SSD is almost full, this could cause problems. Even for writing a small amount of data you need a completely empty block. For this reason SSDs have over-provisioning, which means more storage capacity present than is available.
  36. 36. 36 Advantages and Disadvantages Both SSDs and HDDs do the same job: They boot your system, store your applications, and store your personal files. But each type of storage has its own unique feature set. The question is, what's the difference, and why would a user get one over the other? Lets take a close look at some of the benefits of a solid state drive that might appeal to the consumer: Price: SSDs are very expensive in terms of dollar per GB. For the same capacity and form factor 1TB internal 2.5-inch drive, you'll pay about $75 for an HDD, but as of this writing, an SSD is a whopping $600. That translates into eight-cents-per-GB for the HDD and 60 cents per GB for the SSD. Other capacities are slightly more affordable (250 to 256GB: $150 SSD, $50 HDD), but you get the idea. Since HDDs are older, more established technologies, they will remain less expensive for the near future. Those extra hundreds may push your system price over budget. Maximum and Common Capacity: As seen above, SSD units top out at 1TB, but those are still very rare and expensive. You're more likely to find 128GB to 500GB units as primary drives in systems. You'd be hard pressed to find a 128GB HDD in a PC these days, as 250 or even 500GB is considered a "base" system in 2014. Multimedia users will require even more, with 1TB to 4TB drives as common in high-end systems. Basically, the more storage capacity, the more stuff (photos, music, videos, etc.) you can hold on your PC. While the (Internet) cloud may be a good place to share these files between your phone, tablet, and PC, local storage is less expensive, and you only have to buy it once.
  37. 37. 37 SYSTEM PERFORMANCE – Speed: This is where SSDs shine. An SSD-equipped PC will boot in seconds, certainly under a minute. A hard drive requires time to speed up to operating specs, and will continue to be slower than an SSD during normal operation. The typical SSD starts up in about 15 seconds compared to a hard drive which takes over a minute. In considering the value of your time, a typical person starts their computer 5 times a day which would be a savings of 3 3/4 minutes per day of just under a full day a year…waiting for your computer to start. A PC or Mac with an SSD boots faster, launches apps faster, and has higher overall performance. Witness the higher PCMark scores on laptops and desktops with SSD drives, plus the much higher scores and transfer times for external SSDs vs. HDDs. Whether it's for fun, school, or business, the extra speed may be the difference between finishing on time or failing. System performance represents the most important aspect of hard drive to SSD transition which is why we left it to last. This is initially evident in startup times which are a result of the incredibly fast disk access speed of the SSD which is typically 90 times faster than the hard drive. It also filters down to application loading and general system performance, the reason of which comes down to basic mechanics of the two:  a hard drive requests the information to which an arm must then hover over the magnetic disk containing data which, as we now know, spins at about 67mph. Once it locates the information, it must pick it up from the disk and, in the case of the hard drive, several passes must be made which slows the hard drive significantly.  an SSD on the other hand, works similar to oil moving through a pipeline where all is moved in one trip. In fact, because the typical SSD operates on eight channels (or paths to the controller), it is similar to eight pipelines returning with the information. In terms of gaming SSDs help a lot with texture loading and level loading. With large levels load times can be dropped by over 50%. Also, due to the fast access times many textures will load near instantly and give you more consistent FPS overall. In turn that will give you an overall better gaming experience.
  38. 38. 38 Fragmentation: Because of their rotary recording surfaces, HDD surfaces work best with larger files that are laid down in contiguous blocks. That way, the drive head can start and end its read in one continuous motion. When hard drives start to fill up, large files can become scattered around the disk platter, which is otherwise known as fragmentation. While read/write algorithms have improved where the effect in minimized, the fact of the matter is that HDDs can become fragmented, while SSDs don't care where the data is stored on its chips, since there's no physical read head. SSDs are inherently faster. Durability (Practically Indestructible and Environmental Factors): An SSD has absolutely no moving parts, whereas a hard drive has a disk that spins as high as 7200RPM typically, or 67 miles per hour on its outer edge. As you can imagine, this becomes a natural concern for such things as battery life, temperature, and endurance. The hard drive is depicted on the left with SSD on the right. Solid state drives have been dropped from multistory buildings, run over by cars, used as hockey pucks while a player takes a slapshot and they have even been taped to the side of rockets simply to prove that they are as close to indestructible as it gets. Most hard drives park their read/write heads when the system is off, but they are flying over the drive platter at hundreds of miles an hour when they are in operation. Besides, even parking brakes have limits. If you're rough on your equipment, a SSD is recommended.
  39. 39. 39 The typical SSD can function in extreme high and low temperatures along with its ability to withstand extreme shock and force. The Corsair Force GT, shows that it is able to operate in temperatures from -20 to 85 degC, 90% humidity, up to an altitude of 10,000 feet and can withstand the force of 1500G. Here is a first hand demonstration from Memoright at Computex: Availability: Hard drives are simply more plentiful. Look at the product lists from Western Digital, Toshiba, Seagate, Samsung, and Hitachi, and you'll see many more HDD model numbers than SSDs. For PCs and Macs, HDDs won't be going away completely, at least for the next couple of years. You'll also see many more HDD choices than SSDs from different manufacturers for the same capacities. SSD model lines are growing in number, but HDDs are still the majority for storage devices in PCs.
  40. 40. 40 Form Factors: Because HDDs rely on spinning platters, there is a limit to how small they can be manufactured. There was an initiative to make smaller 1.8-inch spinning hard drives, but that's stalled at about 320GB, since the MP3 player and smartphone manufacturers have settled on flash memory for their primary storage. SSDs have no such limitation, so they can continue to shrink as time goes on. SSDs are available in 2.5-inch laptop drive-sized boxes, but that's only for convenience, as stated above. As laptops become slimmer and tablets take over as primary Web surfing platforms, you'll start to see the adoption of SSDs skyrocket. Noise: Even the quietest HDD will emit a bit of noise when it is in use from the drive spinning or the read arm moving back and forth, particularly if it's in a system that's been banged about or in an all-metal system where it's been shoddily installed. Faster hard drives will make more noise than slower ones. SSDs make virtually no noise at all, since they're non-mechanical. Battery Life: The increased battery life of laptops with SSDs has been very evident. Today, we are seeing typical manufacturer advertisements of eight hour battery life while a few have been able to reach the ten hour mark. SSDs use significantly less power at peak load than hard drives, less than 2W vs. 6W for an HDD. Their energy efficiency can deliver longer battery life in notebooks, less power strain on system, and a cooler computing environment
  41. 41. 41 End Life Data Integrity: When a hard drive reaches end life and crashes, the information is gone. When a SSD reaches end life, it does not crash. It simply prevents further writing to the SSD and all information contained is fully accessible. In fact, there have yet to be any predictions as to how long this information will last other than the life of the NAND flash memory for which the data is stored. Most SSDs have a MTBF of about 1 million hours plus (it's actually 1 million writes). Simply put, you can usually get 5-20 years depending on the NAND and usage of the drive. 200+TB of write life. As far as longevity goes, while it is true that SSDs wear out over time (each cell in a flash memory bank has a limited number of times it can be written and erased), thanks to TRIM technology built into SSDs that dynamically optimizes these read/write cycles, you're more likely to discard the system for obsolescence before you start running into read/write errors. The possible exceptions are high-end multimedia users like video editors who read and write data constantly, but those users will need the larger capacities of hard drives anyway. Hard drives will eventually wear out from constant use as well, since they use physical recording methods. Longevity is a wash when it's separated from travel and ruggedness concerns. The NAND flash used in SSDs can only be used for a finite number of writes. Why? Because SSDs can't write a single bit of information without first erasing and then rewriting very large blocks of data at one time. Each time a cell goes through an erase cycle, some charge is left in the floating-gate transistor, which changes its resistance. As the resistance builds, the amount of current required to change the gate increases. Eventually, the gate can't be flipped at all, rendering it useless. This decaying process doesn't affect the read capabilities of SSD, because reading only requires checking, not changing, the voltages of cells. As a result, NAND flash can "rot" into a read-only state. Some manufacturers use something called wear-leveling to counteract the degradation of NAND flash. This technique distributes data writes across all blocks to make sure the flash memory wears evenly, but even with that, SSDs will decay over time. NAND flash memory of the single-level cell variety generally delivers 50,000 program/erase cycles. Flash of the multi-level cell variety -- the kind used in consumer-level products -- wears out after about 5,000 cycles. For this reason, many data centers and techies use a combination of SSD and HDD. One approach is to use a solid-state drive in a laptop and a traditional hard drive as external storage holding music, photos and other files. This combines the best of both worlds -- the ultrafast, random data access of SSD with the relatively inexpensive, high capacity of HDD.
  42. 42. 42 SSD write performance may degrade when the drive is close to being filled or if you are constantly writing and erasing data to the drive without ample time for GC to take effect. The thing is that SSDs need some "clean" pages when writing data. Otherwise, they have to do a read-modify-write of a "dirty" block instead of just a write to a "clean" page. This process is basically garbage collection at run time and impacts your real time usage rather than preemptive garbage collection. So if you have little free space left and then pound the SSD with a bunch of random writes and do not allow the SSD to clean itself, the can be a noticeable performance degradation. Overall: HDDs win on price, capacity, and availability. SSDs work best if speed, ruggedness, form factor, noise, or fragmentation (technically a part of speed) are important factors to you. If it weren't for the price and capacity issues, SSDs would be the winner hands down. The Right Storage for You So, does an SSD or HDD (or a hybrid of the two) fit your needs? Let's break it down: HDDs • Multimedia Mavens and heavy downloaders: Video collectors need space, and you can only get to 4TB of space cheaply with hard drives. • Budget buyers: Ditto. Plenty of space for cheap. SSDs are too expensive for $500 PC buyers. • Graphics Arts: Video and photo editors wear out storage by overuse. Replacing a 1TB hard drive will be cheaper than replacing a 500GB SSD. • General users: Unless you can justify a need for speed or ruggedness, most users won't need expensive SSDs in their system. SSDs • Road Warriors: People that shove their laptops into their bags indiscriminately will want the extra security of a SSD. That laptop may not be fully asleep when you violently shut it to catch your next flight. This also includes folks that work in the field, like utility workers and university researchers. • Speed Demons: If you need things done now, spend the extra bucks for quick bootups and app launches. Supplement with a storage SSD or HDD if you need extra space (see below). • Graphics Arts and Engineering: Yes, I know I said they need HDDs, but the speed of a SSD may make the difference between completing two proposals and completing five for your client. These users are prime candidates for dual-drive systems (see below). • Audio guys: If you're recording music, you don't want the scratchy sound from a hard drive intruding. Go for the quieter choice.
  43. 43. 43 Now, we're talking primarily about internal drives here, but the same applies to external hard drives. External drives come in both large desktop form factors and compact portable form factors. SSDs are becoming a larger part of the external market as well, The same sorts of affinities apply, i.e., road warriors will want an external SSD over a HDD if they're rough on their equipment. Hybrid Drives and Dual-Drive Systems Back in the mid 2000s, some of the hard drive manufacturers like Samsung and Seagate theorized that if you add a few GB of flash chips to a spinning HDD, you'd get a so-called "hybrid" drive that approaches the performance of an SSD, with only a slight price difference with a HDD. All of it will fit in the same space as a "regular" HDD, plus you'd get the HDD's overall storage capacity. The flash memory acts as a buffer for oft-used files (like apps or boot files), so your system has the potential for booting faster and launching apps faster. The flash memory isn't directly accessible by the end user, so they can't, for example, install Windows or Linux on the flash chips. In practice, drives like the Seagate Momentus XT work, but they are still more expensive and more complex than simple hard drives. They work best for people like road warriors who need large storage, but need fast boot times, too. Since they're an in-between product, they don't necessarily replace dedicated HDDs nor SSDs. In a dual-drive system, the system manufacturer will install a small SSD primary drive (C:) for the operating system and apps, while adding a large storage drive (D: or E:) for your files.While in theory this works well, in practice, manufacturers can go too small on the SSD. Windows itself takes up a lot of space on the primary hard drive, and some apps can't be installed on the D: or E: drive. Some capacities like 20GB or 32GB may be too small. Space concerns are like any multi-drive system: You need physical space inside the PC chassis to hold two (or more) drives. Last but not least, an SSD and an HDD can be combined (like Voltron) on systems with technologies like Intel's Smart Response Technology. SRT uses the SSD invisibly to help the system boot faster and launch apps faster. Like a hybrid drive, the SSD is not directly accessible by the end user; rather, it acts as a cache for files the system needs often (you'll only see one drive, not two). Smart Response Technology requires true SSDs, like those in 2.5-inch form factors, but those drives can be as small as 8GB to 20GB and still provide performance boosts. Since the operating system isn't being installed to the SSD directly, you avoid the drive space problems of the dual-drive configuration mentioned above.
  44. 44. 44 On the other hand, your PC will require space for two drives, a requirement that may exclude some small form factor desktops and laptops. You'll also need the SSD and your system's motherboard to support Intel SRT for this scenario to work. All in all it's an interesting workaround.
  45. 45. 45 How to Determine the Lifespan The useful life of an SSD is governed by three key parameters: SSD NAND flash technology, capacity of the drive, and the application usage model. In general the following life cycle calculator can be used to figure how long the drive will last. Life [years] = (Endurance [P/E cycles] * Capacity [physical, bytes] * Overprovisioning Factor) / (Write Speed [Bps] * Duty Cycle [cycles] * Write % * WAF) / (36 *24* 3,600) Parameters: Endurance, NAND P/E Cycle: 100K SLC, 30K eMLC, 3K MLC Capacity: Usable capacity of the SSD Overprovisioning Factor: Over provision NAND percentage Write Speed: Speed of write in Bytes per second Duty Cycle: Usage duty cycle Write %: percentage of writes during SSD usage WAF: Controller Write Amplification factor computed based on application use case
  46. 46. 46
  47. 47. 47 Applications Development and adoption of SSDs has been driven by a rapidly expanding need for higher input/output performance. High performance laptops, desktops or any application that needs to deliver information in real-time or near real-time can benefit from SSDs. SSDs are best suited to applications that require the highest performance. I/O- intensive applications such as databases, data mining, data warehousing, analytics, trading, high-performance computing, server virtualization, Web serving and email system are most suitable for SSD use. SSDs consume far less power than traditional hard drives, which means they preserve battery life and stay cooler. They're also super quiet, with none of the whirring and clicking you get with HDDs.
  48. 48. 48 Servers SSDs deliver ultra‐high performance input/output operations per second (IOPS), and very low latency for transaction‐intensive server and storage applications. Properly used in systems with HDDs, they reduce total cost of ownership (TCO) through low power consumption and low operating temperature. SSDs are best suited to applications that require the highest performance. I/O- intensive applications such as databases, data mining, data warehousing, analytics, trading, high-performance computing, server virtualization, Web serving and email system are most suitable for SSD use.  SLC SSD is the preferred technology for write caching, and read caching applications where reads are random and write intensive.  eMLC SSD will increasingly become the preferred option when handling a mix of both reads and writes, and especially advantageous when budgets are tight.  MLC SSD is the most cost effective solution for read intensive applications such as accessing a database table. OLTP -> Online transaction processing DSS -> Decision Support System (DSS) HPC -> High-performance computing
  49. 49. 49 Data is stored on integrated circuits that can withstand significant shock and vibration. In fact, enterprise SSDs operate in a wider thermal operating range and wider operational vibration range than HHDs and deliver a significantly longer mean time between failures (MTBF)—2.0 million hours for SSDs, compared to 1.5 million hours for HDDs. Simply put, SSDs last longer, and in many applications, fewer are required. Having fewer drives that last longer means that datacenter operators spend less of their time diagnosing and replacing failed devices. Desktop Computers,Laptops,Ultrabooks The bigger the drive the better. One thing to notice is that with most 60/64GB SSDs is that their 120/128GB and larger counterparts usually have twice the lifespan. You get more space for wear leveling, you get longer life spans due to usually more NAND chips used, and performance usually scales with size as well. If you are wondering whether to get 1 large SSD or 2 or more smaller ones and RAID 0 them or just leave them as separate drives, it’s better to suggest you to simply get the single larger drive.  Smallish boot drive: (~64GB) - With a 64GB drive you get ~59.6GB of formatted space. With a 60GB drive you get ~55.9GB of space. If you want to install the OS, all the programs that you want, and a game or two, then a 60/64 GB SSD will do.  Medium sized boot drive: (~128GB) - With a 128GB drive you get ~119.24GB of formatted space. With a 120GB drive you get ~111.79GB of space. If you want to install the OS, all the programs that you want, a few games and a 120/128GB SSD at least is recommended.  Large boot drive: (~256GB+) - If you want to have Steam or most/all of your games or other large items on your SSD at least a 240/256 GB SSD is recommended.
  50. 50. 50 Usually due to hardware limitations and power saving features in laptops SSDs will perform slightly slower than in their desktop counterparts. But the difference is usually only seen in benchmarks. SSD as Cache HD Camcorder,Smart TV,Set Top Boxes,CCTVs and Gaming Consoles - for primary storage
  51. 51. 51 While gaming :
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  53. 53. 53 Conclusion First time users are often amazed at the fact that every press of the keyboard is met with as close to instant response as one could imagine. It is a very visible upgrade from a hard drive system and renders a great deal more enjoyment as well as productivity at the end of the day. Upgrading your regular old hard drive to a solid-state drive is one of the best upgrades you can make to your computer nowadays, as our hard drives tend to be among the biggest bottlenecks in performance. Understanding the different types of SSDs can, not only help you out in your understanding of such, but also, can better equip and help save a great deal of money in your final purchase decision. The SSD, much like the Internet when it first came to light, was originally touted as a passing phase. It has quickly found a position where, if manufacturers can find the lower prices, higher storage capacity and availability, the SSD could threaten the mere existence of the HD. The first obstacle of performance was surpassed long before many knew what SSD stood for. It's unclear whether SSDs will totally replace traditional spinning hard drives, especially with shared cloud storage waiting in the wings. The price of SSDs is coming down, but still not enough to totally replace the TB of data that some users have in their PCs and Macs. Cloud storage isn't free either: you'll continue to pay as long as you want personal storage on the Internet. There appears to be so many benefits that we just cannot ignore the SSD on a business or personal use level. Although it will need to gain a foundation in the spiderweb designs of small and large office networks, the simplicity of the SSD lies in the absolutely lightning speed in which it accomplishes its tasks at the individual user level of both. Cost has been one of the biggest hurdles of flash memory and, consequently, of solid-state drives. But in recent years, costs have dropped significantly. At the same time, advances in NAND flash development have taken what's good about the technology and made it even better Historically, SSDs have been much more expensive than conventional hard drives. Due to improvements in manufacturing technology and expanded chip capacity, however, prices have dropped, leading both consumers and enterprise-level customers to re-evaluate SSDs as viable, if still expensive, alternatives to conventional storage.
  54. 54. 54 Quicker startup, incredible performance, no moving parts, less heat, longer battery life, incredible reliability and durability will soon enough conquer the obstacles of price, storage restrictions and availability.
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  56. 56. 56 References http://www.thessdreview.com Shyam Jos, Blogger at FAQsPedia Prof Hong Jiang – Department of CSE,University of Nebraska – Lincoln http://www.notebookreview.com http://computer.howstuffworks.com/ Dennis Martin ,Demartek AnandTech.com Wikipedia Google Crucial.com

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