Memory and storage

1. MEMORY AND STORAGE

2. STORAGE DEVICE
A storage device is any computing
hardware, that is used for storing and
managing data for later use.

3. Computer data storage
• Computer data storage, often called
storage or memory, refers to
computer components and recording
media that retain digital data used
for computing for some interval of
time.

4. Purpose ofstorage
Many different forms of storage, based on
various natural phenomena, have been
invented. So far, no practical universal storage
medium exists, and all forms of storage have
some drawbacks. Therefore a computer system
usually contains several kinds of storage, each
with an individual purpose.

5. History
1928- magnetic tape - fritz pfleumer
1932- magnetic drum - G Taushek
1946- Williams tube - prof. Tredrick C Willam
memory technology mostly permitted a capacity of a few bytes.
The first electronic programmable digital computer,
the ENIAC, using thousands of octal-base radio vacuum
tubes, could perform simple calculations involving 20 numbers
of ten decimal digits which were held in the vacuum
tube accumulators.
1956- Hard disk -
1963- Music tape - philips
1966- DRAM - Robert H Dennard
1980- CD - James T Russel

6. Fundamental storage technologies
• Semiconductor (dynamic random access
memory ,ROM,Cache Memory,Registers,Flash
memory)
• Magnetic (Floppy disk , Hard disk drive,
Magnetic tape data storage )
• Optical (CD, DVD)
• Paper (Paper tape, punch card)

7. Introduction to Memory
 In computing, memory refers to the physical
devices used to store programs (sequences of
instructions) or data (e.g. program state information)
on a temporary or permanent basis for use in
a computer or other digital electronic device.
 The term primary memory is used for the
information in physical systems which are fast
(i.e. RAM), as a distinction from secondary memory,
which are physical devices for program and data
storage which are slow to access but offer higher
memory capacity.
 Primary memory stored on secondary memory is
called "virtual memory".

8. Memory is of two types:-
1. Primary memory (RAM,ROM,CACHE,FLASH)
2. Secondary memory (FLOPPY DISK,MAGNETIC
DISK,MAGNETIC TAPES,OPTICAL DISKS)
MEMORY
PRIMARY SECONDARY

9. PRIMARY MEMORY
Primary memory is internal memory of the
computer.RAM and ROM both form part of
primary memory.The primary memory provides
main working space to the computer.
RAM :- The primary storage is referred to as
random access memory because it is possible to
randomly select and use any location of the
memory directly store and retrieve data. It is also
called read/write memory. It is a volatile
memory.

10. READ ONLY MEMORY (ROM)
• The acronym for ROM is Read Only Memory
• when the data is burnt on a ROM, it cannot be removed
nor it cannot be altered it can only read .
• ROM is known as nonvolatile.
• ROM stores programs such as the program that boots
the computer.
• ROMs are widely used in calculators and other devices
such as laser printers.

11. TYPES OF ROM
There are five basic ROM types:-
1. Masked ROM (READ ONLY MEMORY)
2. PROM (PROGRAMMABLE ROM)
3. EPROM (Erasable Programmable
ROM)
4. EEPROM (Electrically erasable programmable
ROM)
5. FLASH MEMORY(ONE KINDS OF EEPROM)

12. IMPROTANT POINTS OF
ROM
Masked ROM:
• In this type of ROM bits are stored permanently by
marking and metallization process. This is done by
manufacturers. This type of ROM can be programmed
only one-by the manufacture

13. PROM:
• It is an another type of primary memory in computer,
which is called Programmable Read Only Memory
(PROM).It si not possible to modify or erase programs
stored in ROM,but is possible for you to store your
program in PROM. Once the programmers, are written it
cannot be changed and remain intact even if power is
switched off.

14. EPROM:
The Erasable PROM chip allows the stored data to
erased and new data can be reprogrammed.
Information store in EPROM exposing the chip for
some time ultraviolet light and it erases chip is
reprogrammed using a special programming
facility. When the EPROM is in use information
can only be read.

15. EEPROM:
• In an electricity erasable PROM, the
contents of cells can be erased by the
application of a high voltage. Advantages
with EEPROMs are : it need not be
physically removed for reprogramming and
the process can be made selective since
electrical erasure is used.

16. The advantages of ROM are
• They are non-volatile
• They are cheaper than RAM
• They are static and do not refreshing
• They are more reliable than RAM as their
circuit is simple.
• They are available in longer sizes than
RAM.
• They are easier to interface than RAM.

17. CACHE :-
A small memory chip is attached between CPU
and main memory , whose access time is very
close to the processing speed of CPU .It is called
cache memory. Its physical location is in CPU and
is much faster than RAM. Its size is normally small.
We can see the cache memory of CPU in BIOS
setup.

19. FLASH MEMORY
• The flash memory is a type of chip that is called as the EEPROM.
• BIOS of computer, the memory stick that is found in the digital
cameras , USB pen drives , the memory cards of the mobiles etc are
the example of flash memory.
• The important properties of the flash memory are that it is much fast
and very much easier in use .
• Flash drive can be efficiently used for the purpose of a hard disk.

20. Advantages of flash memory
when used as a hard disk
• Advantage of the flash memory over the hard disk is that
it is compact and much efficient for the data transfer.
• There are no mobile parts in it As in the hard disk there
are the platters and the read write head moves over it.
• There is no such mechanical component in the flash
memory drive. Hence it is a purely electronic device.
• The flash memory is quite expensive as compared to the
hard disk drive, but it is light in weight

21. SECONDARY MEMORY
Secondary memory is external and
permanent in nature. The secondary
memory is concerned with magnetic
memory. Secondary memory can be
stored on storage media like FLOPPY
DISK,MAGNETIC DISK,MAGNETIC
TAPES,OPTICAL DISKS,SSD etc.

22. Characteristics of storage
PERFORMANCE
CAPACITY
VOLATILITY
DIFFERENTIATION
MUTABILITY
ACCESSIBILITY

23. Characteristics of storage
1. PERFORMANCE:-
• Throughput:-The rate at which information can be read from or written
to the storage. In computer data storage, throughput is usually expressed in
terms of megabytes per second or MB/s, though bit rate may also be used.
The relevant unit of measurement is typically nanosecond for primary storage,
millisecond for secondary storage, and second for tertiary storage.

24. • 2. CAPACITY:-
• Raw capacity
• The total amount of stored information that a storage
device or medium can hold. It is expressed as a quantity
of bits or bytes (e.g. 10.4 megabytes).
Memory storage density
• The compactness of stored information. It is the storage
capacity of a medium divided with a unit of length, area
or volume (e.g. 1.2 megabytes per square inch).

25. VOLATILITY:-
Volatility is a term used in information processing.
It refers to the percentage of records that are
added to or deleted from a file during a single
processing operation. A data file that has a high
percentage of change would be described as
having a high volatility.
Volatile refers to storage devices that will lose all
their data if the power is switched off.

26. • Differentiation:-
• Dynamic random access memory A form of volatile
memory which also requires the stored information to be
periodically reread and rewritten, or refreshed,
otherwise it would vanish.
• Static memory
• A form of volatile memory similar to DRAM with the
exception that it never needs to be refreshed as long as
power is applied. (It loses its content if power is
removed).

27. Mutability:-
• Read/write storage or mutable storage :- Allows information to be
overwritten at any time. A computer without some amount of
read/write storage for primary storage purposes would be useless
for many tasks. Modern computers typically use read/write storage
also for secondary storage.
• Read only storage :-
• Retains the information stored at the time of manufacture, and write
once storage (Write Once Read Many) allows the information to be
written only once at some point after manufacture.
• Slow write, fast read storage:-
• Read/write storage which allows information to be overwritten
multiple times, but with the write operation being much slower than
the read operation. Examples include CDRW and flash memory.

28. Accessibility:-
• Random access:-Any location in storage can be
accessed at any moment in approximately the same
amount of time. Such characteristic is well suited for
primary and secondary storage.
• Sequential access:-
The accessing of pieces of information will be in a serial
order, one after the other; therefore the time to access a
particular piece of information depends upon which piece
of information was last accessed. Such characteristic is
typical of offline storage.

29. Memory management
Memory management is the process of
controlling and coordinating
computer memory, assigning portions
called blocks to various running programs to
optimize overall system performance.
Memory management resides in hardware,
in the OS (operating system), and in
programs and applications.

30.  In hardware, memory management involves
components that physically store data, such as
RAM (random access memory) chips, memory caches,
and flash-based SSDs (solid-state drives).
 In the OS, memory management involves the
allocation (and constant reallocation) of specific
memory blocks to individual programs as user demands
change.
 At the application level, memory management
ensures the availability of adequate memory for
the objects and data structures of each running
program at all times.

31. Virtual Memory
Virtual memory is a stratagem to utilize the hard drive memory to achieve
enhanced performance from the random access memory.
virtual memory is a memory management technique that is implemented
using both hardware and software. It maps memory addresses used by a
program, called virtual addresses, into physical addresses in computer
memory.
The main memory is divided into equal size chunks called page frames
and each page frame has a unique physical address. So whenever a
page needs to be accessed, the operating system has to translate the
virtual address into a physical address and this is done by a Memory
Management Unit (MMU) with the help of mapping in a page table.
automatically translates virtual addresses to physical addresses.

32. Software within the operating system may extend these capabilities to provide a
virtual address space that can exceed the capacity of real memory and
thus reference more memory than is physically present in the computer.
The concept of virtual memory was first
developed by German physicist FritzRudolf
Güntsch at the
Technische Universität Berlin in 1956

36. MEMORY ALLOCATION
Memory allocation is a process by which computer
programs and services are assigned with physical
or virtual memory space.
Memory allocation is the process of reserving a
partial or complete portion of computer memory for
the execution of programs and processes . Memory
allocation is achieved through a process known as
memory management.

37. MEMORY PROTECTION
Memory protection is a way to
control memory access rights on a
computer, and is a part of most modern
operating systems. The main purpose
of memory protection is to prevent a
process from accessing memory that has
not been allocated to it.
This prevents a bug or malware within a
process from affecting other processes, or
the operating system itself.

38. PROCESSOR REGISTERS
In computer architecture, a processor register is
a small amount of storage available as part of a
Digital processor, such as a central processing
unit (CPU). Such registers are typically
addressed by mechanisms other than main
memory and can be accessed faster.

39. Almost all computers, load store architecture or not,
load data from a larger memory into registers where
it is used for arithmetic, manipulated or tested by
machine instructions. Manipulated data is then often
stored back into main memory, either by the same
instruction or a subsequent one. Modern processors
use either static or dynamic RAM as main memory,
with the latter usually accessed via one or more
cache levels.

40. Processor registers are normally at the top of
the memory hierarchy, and provide the fastest
way to access data.
Registers are normally measured by the
number of bits they can hold, for example, an
"8bit register" or a "32bit register". A processor
often contains several kinds of registers, that
can be classified according to their content or
instructions that operate on them:

41. Cache memory
Cache memory is a small amount of fast memory
∗ Placed between two levels of memory hierarchy
» To bridge the gap in access times
– Between processor and main memory (our focus)
– Between main memory and disk (disk cache)
∗ Expected to behave like a large amount of fast memory

43. TYPES OF CACHE
Separate instruction and data caches
» Initial cache designs used unified caches
» Current trend is to use separate caches (for level 1)

44. Several reasons for preferring separate caches
∗ Locality tends to be stronger
∗ Can use different designs for data and instruction caches
» Instruction caches
– Read only, dominant sequential access
– No need for write policies
– Can use a simple direct mapped cache implementation
» Data caches
– Can use a set-associative cache
– Appropriate write policy can be implemented
∗ Disadvantage
» Rigid boundaries between data and instruction caches

45. Hierarchy of storage
• Primary storage
• Secondary storage or external memory
• Tertiary storage
• Off-line storage
• Network Storage

46. Secondary storage or external
memory
• it is not directly accessible by the CPU.
• it is non-volatile
• hard disk drive, SSD, CD , DVD,Blue Ray,
floppy disks, magnetic tape, paper tape,
punched cards are the example of this.
• It need to be formatted before they can
store data.

47. Tertiary storage
• Provides a third level of storage .
• This is not a popular storage device
• Its main use is for storing data at a very large
scale.
• It require a database to organize the data that
are stored in them, and the computer needs to
go through the database to access those data.
• tape libraries , optical jukeboxes are the
example of this

48. Large tape library

49. Off-line storage
 Its another name is disconnected storage.
It is not directly connected to the computer and is used
as a transfer medium only.
Offline storage devices are remotely located and
accessed as per need only.
This storage devices also needs human intervention to
be read properly by the main computer system.
It serves as a good backup device since it is remotely
located.
It also provides good security for data since you can not
easily access it from a computer.

50. NETWORK STORAGE
• A NAS unit is a computer connected to a network that
provides only file based data storage services to other
devices on the network. Although it may technically be
possible to run other software on a NAS unit, it is not
designed to be a general purpose server. For example, NAS
units usually do not have a keyboard or display, and are
controlled and configured over the network, often using a
browser.

51. Magnetic storage
Magnetic storage or magnetic recording is the
storage of data on a magnetised medium. Magnetic
storage uses different patterns of magnetisation in a
magnetisable material to store data and is a form
Of nonvolatile memory. The information is accessed
using one or more read/write heads.
Example- hard disk , Solid state disk, Floopy disk,
Magnetic tape.

52. Floppy Disk
A floppy disk, also called a diskette, is a disk storage medium
composed of a disk of thin and flexible magnetic storage
medium, sealed in a rectangular plastic carrier lined with
fabric that removes dust particles. Floppy disks are read and
written by a floppy disk drive (FDD).
Floppy disks, initially as 8inch (200 mm) media and later in
5¼inch (133 mm) and 3½inch (90 mm) sizes

54. Disk format Year
introduced
Formatted storage
capacity
Marketed
capacity
3½inch HD 1987 1440 kB (1760 kB on
Amiga)
1.44 MB (2.0
MB
unformatted)
3½inch ED 1987 2880 kB 2.88 MB
3½inch Floptical
(LS)
1991 20385 kB 21 MB
3½inch Superdisk (LS120) 1996 120.375 MB 120 MB
3½inch Superdisk (LS240) 1997 240.75 MB 240 MB
3½inch HiFD 1998/99 1998/99 150/200 MB
HD = High Density; ED = Extended Density;
LS = Laser Servo; HiFD = High capacity Floppy Disk;
SS = Single Sided;
DS = Double Sided

55. Hard disk
A hard disk drive (often shortened as hard disk, hard drive,
or HDD) is a non-volatile storage device.
A hard disk drive (HDD), hard disk, hard drive or fixed disk
is a data storage device used for storing and retrieving
digital information using one or more rigid ("hard") rapidly
rotating disks (platters) coated with magnetic material.
The platters are paired with magnetic heads arranged on a
moving actuator arm, which read and write data to the
platter surfaces. Data is accessed in a random access
manner, meaning that individual blocks of data can be
stored or retrieved in any order rather than sequentially.
HDDs retain stored data even when powered off.

56. Introduced by IBM in 1956,HDDs became the dominant
secondary storage device for general purpose computers
by the early 1960s. Continuously improved, HDDs have
maintained this position into the modern era of servers and
personal computers. More than 200 companies have
produced HDD units, though most current units are
manufactured by Seagate, Toshiba and Western Digital.
The primary characteristics of an HDD are its capacity and
performance. Capacity is specified in unit prefixes
corresponding to powers of 1000: a 1terabyte (TB) drive
has a capacity of 1,000 gigabytes (GB; where 1 gigabyte =
1 billion bytes).
Capacity – 80 GB,160 GB, 250 GB,320 GB,500 GB, 1 TB

57. The two most common form factors for modern HDDs are
3.5inch, for desktop computers, and 2.5inch, primarily for
laptops. HDDs are connected to systems by standard
interface cables such as SATA (Serial ATA), USB cables.

59. MECHANISM
HDDs record data by magnetizing ferromagnetic material
directionally, to represent either a 0 or a 1 binary digit. They
read the data back by detecting the magnetization of the
material. A typical HDD design consists of a spindle that holds
one or more flat circular disks called platters, onto which the
data is recorded. The platters are made from a non-magnetic
material, usually aluminum alloy or glass, and are coated with
a thin layer of magnetic material, typically 10–20 nm in
thickness with an outer layer of carbon for protection. Older
disks used iron(III) oxide as the magnetic material, but current
disks use a cobalt-based alloy.

60. Magnetic tape
Magnetic tape is a medium for magnetic recording,
made of a thin magnetizable coating on a long,
narrow strip of plastic film. It was developed in
Germany, based on magnetic wire recording.
Devices that record and play back audio and video
using magnetic tape are tape recorders and video
tape recorders. A device that stores computer data
on magnetic tape is a tape drive (tape unit,
streamer).

61. Data storage
Magnetic tape was first used to record computer data
in 1951. The recording medium was a thin strip of one
half inch (12.65 mm) wide metal, consisting of nickel
plated bronze (called Vicalloy). Recording density was
128 characters per inch (198 micrometre/character) on
eight tracks.
Modern cartridge formats include LTO(LINEAR TAPE
OPEN), DLT(DIGITAL LINEAR TAPE), and
DAT(DIGITAL AUDIO TAPE).

63. RANDOM ACCESS MEMORY
RAM (random access memory) is the place in a
computer where the operating system, application
programs, and data in current use are kept so that
they can be quickly reached by the computer's
processor.
RAM is much faster to read from and write to than
the other kinds of storage in a computer, the hard
disk, floppy disk, and CD-ROM. However, the data
in RAM stays there only as long as your computer is
running. When you turn the computer off, RAM
loses its data.

64. When you turn your computer on again, your operating
system and other files are once again loaded into RAM,
usually from your hard disk.
The two main forms of modern RAM are static RAM
(SRAM) and dynamic RAM (DRAM).

65. Dynamic Random Access Memory (DRAM)
A memory chip that depends upon an applied voltage to
keep the stored data.
Dynamic random access memory (DRAM) is a type of
random access memory that stores each bit of data in a
separate capacitor within an integrated circuit. The capacitor
can be either charged or discharged; these two states are
taken to represent the two values of a bit, conventionally
called 0 and 1.
Since even "non conducting" transistors always leak a small
amount, the capacitors will slowly discharge, and the
information eventually fades unless the capacitor charge is
refreshed periodically. Because of this refresh requirement, it
is a dynamic memory as opposed to static random access
memory (SRAM) and other static types of memory.

66. The main memory (the "RAM") in personal computers
is dynamic RAM (DRAM). It is the RAM in desktops,
laptops and workstation computers as well as some
of the RAM of video game consoles.
The advantage of DRAM is its structural simplicity:
only one transistor and a capacitor are required per
bit, compared to four or six transistors in SRAM. This
allows DRAM to reach very high densities.

67. General DRAM formats Dynamic random access memory is
produced as integrated circuits (ICs) bonded and mounted into
plastic packages with metal pins for connection to control signals
and buses. In early use individual DRAM ICs were usually either
installed directly to the motherboard or on ISA expansion cards;
later they were assembled into multichip Plugin modules (DIMMs,
SIMMs, etc.). Some standard module types are: DRAM chip
(Integrated Circuit or IC) Dual inline Package (DIP) DRAM
(memory) modules Single Inline Pin Package (SIPP) Single Inline
Memory Module (SIMM) Dual Inline Memory Module (DIMM)
Rambus Inline Memory Module (RIMM), technically DIMMs but
called RIMMs due to their proprietary slot. Small outline DIMM
(SODIMM), about half the size of regular DIMMs, are mostly used
in notebooks, small footprint PCs (such as MiniITX motherboards),
upgradable office printers and networking hardware like routers.
Small outline RIMM (SORIMM). Smaller version of the RIMM,
used in laptops. Technically SODIMMs but called SORIMMs due to
their proprietary slot.

68. Common DRAM modules
Common DRAM packages as illustrated to the right, from top to bottom (last three
types are not present in the group picture, and the last type is available in a
separate picture):
DIP 16pin (DRAM chip, usually prefast page mode DRAM (FPRAM))
SIPP 30pin (usually FPRAM)
SIMM 30pin (usually FPRAM)
SIMM 72pin (often extended data out DRAM (EDO DRAM) but FPRAM is not uncommon)
DIMM 168pin (most SDRAM but were some extended data out DRAM (EDO DRAM))
DIMM 184pin (DDR SDRAM)
RIMM 184pin (RDRAM)
DIMM 240pin (DDR2 SDRAM and DDR3 SDRAM)
DIMM 288pin (DDR4 SDRAM)
SIMM- single in-line memory module
DIMM-dual in-line memory module
RIMM- rambus in-line memory module

69. COMMON SODIMM DRAM modules
72pin (32bit)
144pin (64bit) used for SODIMM SDRAM
200pin (72bit) used for SODIMM DDR SDRAM and
SODIMM DDR2 SDRAM
204pin (64bit) used for SODIMM DDR3 SDRAM
260pinused for SODIMM DDR4 SDRAM

71. STSTIC RANDOM ACCESS MEMORY
Static random access memory (SRAM or static RAM) is a
type of semiconductor memory that uses bistable latching
circuitry (Flipflop) to store each bit. The term static
differentiates it from dynamic RAM (Dynamic random access
memory) which must be periodically refreshed. SRAM
exhibits data remanence,but it is still volatile in the
conventional sense that data is eventually lost when the
memory is not powered.
SRAM is more expensive and less dense than DRAM and is
therefore not used for highcapacity, lowcost applications
such as the main memory in personal computers.

72. SOLID STATE DISK
Solid state storage devices store computer data on non-
volatile "flash" memory chips rather than by changing the
surface properties of a magnetic or optical spinning disk.
With no moving parts solid state drives (SSDs) -- are also
very much the future for almost all forms of computer
storage.
As of 2014, most SSDs use NAND based flash memory,
which retains data without power. For applications requiring
fast access, but not necessarily data persistence after
power loss, SSDs may be constructed from random access
memory (RAM). Such devices may employ separate power
sources, such as batteries, to maintain data after power
loss.

74. Flash memory
Flash memory is a non-volatile computer storage that can
be electrically erased and reprogrammed. It is a technology
that is primarily used in memory cards and USB flash drives
for general storage and transfer of data between computers
and other digital products.
It is a specific type of EEPROM (Electrically Erasable
Programmable Read-Only Memory) that is erased and
programmed in large blocks; in early flash the entire chip
had to be erased at once.

75. USB MEMORY STICKS
USB memory sticks (or USB memory keys, USB memory drives, or whatever
you choose to call them!) are basically a combination of a flash memory card
and a flash memory card reader in one handy and tiny package.
As with other storage devices, there are two key factors to consider when
selecting a USB memory stick: capacity and data transfer speed.
It is a function of the type of flash memory chips used to hold the data.
Without going into great technicalities, these chips come in two varieties
called single level cell (SLC) and multi level cell (MLC). Basically, MLC
flash chips store two or more bits of data in each memory cell, whilst SLC
chips store only one. MLC solid state disks are therefore cheaper to
produce than SLC disks at any given capacity, but due to storing more
than one bit of information in each memory cell take longer to write and
read data. If you need a fast USB key, memory card or indeed hard-disk
replacement SSD then you need to pay more to obtain an SLC device.

76. First commercial product
IBM's USB flash drive became available on December 15, 2000, and had a storage
capacity of 8 MB, more than five times the capacity of the then common floppy disks.
In 2000, Lexar introduced a Compact Flash (CF) card with a USB connection, and a
companion card read/writer and USB cable that eliminated the need for a USB hub.
Second generation
By 2013, most USB flash drives had USB 2.0 connectivity, which has 480 Mbit/s as
the transfer rate upper bound; after accounting for the protocol overhead that
translates to a 35 MB/s effective throughput.
Third generation
Like USB 2.0 before it, USB 3.0 dramatically improved data transfer rates compared
to its predecessor. It was announced in late 2008, but consumer devices were not
available until the beginning of 2010. The USB 3.0 interface specifies transfer rates
up to 5 Gbit/s (625 MB/s), compared to USB 2.0's 480 Mbit/s (60 MB/s).

77. Fourth generation
As of March 2015, some manufacturers have announced
USB 3.1 typeC flash drives with read/write speeds of
around 530 MB/s.
Storage capacity
The first USB flash drive appeared on the market in late
2000, providing a storage capacity of 8 MB. Later, the
maximum available storage capacity gradually doubled
(16 MB, 32 MB, etc.) all the way up to reaching capacities
of 512 GB and 1 TB by January 2013. However, as of
May 2014 flash drives with anywhere from 8 to 128 GB
are still frequently sold.

78. USB hub
A USB hub is a device that expands a single Universal Serial Bus (USB)
port into several so that there

79. SD CARDS
solid state storage devices come in two basic forms: flash memory
cards and USB memory sticks.
Flash memory cards were developed as a storage media for digital
cameras and mobile computers. They consist of a small plastic package
with a contact array that slots into a camera or other mobile
computing device, or an appropriate memory card reader.

80. U3
U3 was a joint venture between SanDisk and M-Systems, producing a
proprietary method of launching Windows applications from special USB flash
drives.
Flash drives adhering to the U3 specification are termed
"U3 smart drives".
U3 smart drives come preinstalled with the U3 Launchpad, which looks similar to
the Windows OS start menu and controls program installation.
Applications that comply with U3 specifications are allowed to write files or
registry information to the host computer, but they must remove this information
when the flash drive is ejected.
Customizations and settings are instead stored with the application on the flash
drive.
Microsoft and SanDisk created a successor called StartKey.