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Lec5

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  • 1. Chapter 5Data Storage Technology 1
  • 2. Systems Architecture Chapter 5 Chapter Goals • Describe the distinguishing characteristics of primary and secondary storage • Describe the devices used to implement primary storage • Describe the memory allocation schemes • Compare and contrast secondary storage technology alternatives 2
  • 3. Systems Architecture Chapter 5 Chapter Goals • Describe factors that determine storage device performance • Choose appropriate secondary storage technologies and devices 3
  • 4. Systems Architecture Chapter 5 Chapter Topics • Explore storage devices and their technologies • Outlines characteristics common to all storage devices • Explains the technology strengths and weaknesses of primary storage and secondary storage 4
  • 5. Systems Architecture Chapter 5 Storage Device Characteristics 5
  • 6. Systems Architecture Chapter 5 Storage Device Characteristics • Speed • Volatility • Access method • Portability • Cost and capacity 6
  • 7. Systems Architecture Chapter 5 Storage Device Characteristics Speed • The delay between a user request for program execution and the first prompt for the user input depends on the speed of primary and secondary storage devices. • Primary storage speed is typically greater than secondary storage speed by a factor of 105 or more. 7
  • 8. Systems Architecture Chapter 5 Storage Device Characteristics Speed • Secondary storage device speed is called access time. • The access time for reading and writing is assumed to be the same unless otherwise stated. 8
  • 9. Systems Architecture Chapter 5 Storage Device Characteristics Volatility • A storage device or medium is non-volatile if it holds data without loss over long periods of time. • A storage device or medium is volatile if it cannot reliably hold data for long periods of time. 9
  • 10. Systems Architecture Chapter 5 Storage Device Characteristics Volatility • Primary storage devices are generally volatile. • Secondary storage devices are generally non-volatile. 10
  • 11. Systems Architecture Chapter 5 Storage Device Characteristics • Access Method – Serial Access – Random Access – Parallel Access 11
  • 12. Systems Architecture Chapter 5 Storage Devices Characteristics • Serial Access – stores and retrieve data items in a linear, or sequential order. (Magnetic tape) • Random Access (Direct Access) – access device is not restricted to any specific order when accessing data. (Hard Disk) 12
  • 13. Systems Architecture Chapter 5 Storage Device Characteristics • Parallel Access – a device that is capable of simultaneously accessing multiple storage locations. (Random Access Memory) 13
  • 14. Systems Architecture Chapter 5 Storage Device Characteristics Portability • Data can be made portable by storing it on a removable storage medium or device. • Portable devices typically have slower access speed than permanently installed devices and those with non-removable media. 14
  • 15. Systems Architecture Chapter 5 Storage Device Characteristics Cost and Capability • An increase in speed, permanence or portability generally comes at increased cost if all other factors are held constant. 15
  • 16. Systems Architecture Chapter 5 Storage Device Characteristics 16
  • 17. Systems Architecture Chapter 5 Storage Device Characteristics Memory-Storage Hierarchy • Cost and access speed generally decrease as one moves down the hierarchy. • Due to lower cost, capacity tends to increase as one moves down the hierarchy. 17
  • 18. Systems Architecture Chapter 5 Storage Device Characteristics 18
  • 19. Systems Architecture Chapter 5 Primary Storage Devices • Storing Electrical Signals • Random Access Memory • Read-Only Memory • Memory Packaging 19
  • 20. Systems Architecture Chapter 5 Primary Storage Devices Storing Electrical Signals • Data is represented as electrical signals. • Digital signals are used to transmit data to and from devices attached to the system bus. • Storage devices must accept electrical signals as input and output. 20
  • 21. Systems Architecture Chapter 5 Primary Storage Devices Random Access Memory Random Access Memory describes primary storage devices with these characteristics: – Microchip implementation using semiconductors – Ability to read and write with equal speed – Random access to stored bytes, words, or larger data units 21
  • 22. Systems Architecture Chapter 5 Primary Storage Devices Random Access Memory Two types of memory: – Static RAM (SRAM) – Dynamic RAM (DRAM) – Synchronous DRAM (SDRAM) – Ferroelectric RAM 22
  • 23. Systems Architecture Chapter 5 Primary Storage Devices Static RAM • Implemented with transistors. • Basic unit of storage is a flip-flop circuit. • A flip-flop is an electrical circuit that remembers its last position. • One position represents 1, the other position represents 0. 23
  • 24. Systems Architecture Chapter 5 Primary Storage Devices 24
  • 25. Systems Architecture Chapter 5 Primary Storage Devices Dynamic RAM • Uses transistors and capacitors. • Lose their charge quickly. • Require a fresh infusion of power thousands of times per second. • Each refresh operation is called a refresh cycle. 25
  • 26. Systems Architecture Chapter 5 Primary Storage Operations Synchronous DRAM • Read-ahead RAM that uses the same clock pulse as the system bus. • Read and write operations are broken into a series of simple steps and each step can be completed in one bus clock cycle. 26
  • 27. Systems Architecture Chapter 5 Primary Storage Devices Ferroelectric RAM Embeds iron or iron compounds within a microchip to store bits in much the same manner as old-fashioned core memory. 27
  • 28. Systems Architecture Chapter 5 Primary Storage Devices Read-Only Memory • Electronically Erasable Programmable Read- Only Memory (EEPROM) • Flash Memory 28
  • 29. Systems Architecture Chapter 5 Primary Storage Devices Read-Only Memory – a random access memory device that can store data permanently or semipermanently. Instructions that reside in ROM are called firmware. 29
  • 30. Systems Architecture Chapter 5 Primary Storage Devices Electronically Erasable Programmable Read-Only Memory – can be programmed, erased, and reprogrammed by signals sent from and external control source, such as a CPU. Flash Memory – can be erased and rewritten more quickly. 30
  • 31. Systems Architecture Chapter 5 Primary Storage Devices Memory Packaging • Dual In-line Packages (DIPs) • Single In-line Memory Module (SIMM) • Double In-line Memory Module (DIMM) 31
  • 32. Systems Architecture Chapter 5 Primary Storage Devices 32
  • 33. Systems Architecture Chapter 5 Primary Storage Devices Memory Packaging Memory circuits are embedded within microchips and groups of chips are packed on a small circuit board that can be installed or removed easily. 33
  • 34. Systems Architecture Chapter 5 CPU Memory Access • Physical Memory Organization • Memory Allocation and Addressing 34
  • 35. Systems Architecture Chapter 5 CPU Memory Access Physical Memory Organization Main memory can be regarded as a sequence of contiguous, or adjacent memory cells. 35
  • 36. Systems Architecture Chapter 5 Physical Storage Devices 36
  • 37. Systems Architecture Chapter 5 Memory Allocation and Addressing Memory Allocation – describes the assignment of specific memory addresses to system software, application programs and data. 37
  • 38. Systems Architecture Chapter 5 Memory Allocation and Addressing 38
  • 39. Systems Architecture Chapter 5 Memory Allocation and Addressing Memory Addressing: • Absolute Addressing – describes memory address operands that refer to actual physical memory locations. • Relative Addressing (Indirect Addressing) – automatically computes physical memory addresses. 39
  • 40. Systems Architecture Chapter 5 Memory Allocation and Addressing 40
  • 41. Systems Architecture Chapter 5 Memory Allocation and Addressing 41
  • 42. Systems Architecture Chapter 5 Magnetic Storage Magnetic Storage • Exploit the duality of magnetism and electricity. • Electric current is used to generate a magnetic field. • A magnetic field can be used to generate electricity. 42
  • 43. Systems Architecture Chapter 5 Magnetic Storage 43
  • 44. Systems Architecture Chapter 5 Magnetic Storage Disadvantages of Magnetism • Magnetic decay • Magnetic leakage • Minimum threshold current for read operations • Storage medium coercivity • Long-term storage medium integrity 44
  • 45. Systems Architecture Chapter 5 Magnetic Storage 45
  • 46. Systems Architecture Chapter 5 Magnetic Storage Magnetic Decay and Leakage Magnetic Decay – the tendency of magnetically charges particles to lose their charge over time. Magnetic Leakage – a decrease in the strength of individual bit charges. 46
  • 47. Systems Architecture Chapter 5 Magnetic Storage Storage Density 47
  • 48. Systems Architecture Chapter 5 Magnetic Storage Magnetic Integrity Depends on the nature of the storage medium’s construction and the environmental factors. 48
  • 49. Systems Architecture Chapter 5 Magnetic Storage Magnetic Storage Devices: • Magnetic Tape • Magnetic Disk 49
  • 50. Systems Architecture Chapter 5 Magnetic Storage Magnetic Tape • Ribbon of plastic with a coercible surface coating. • Mounted in a tape drive for reading and writing. • Compound the magnetic leakage problem by winding the tape upon itself. 50
  • 51. Systems Architecture Chapter 5 Magnetic Storage Magnetic Tape Approaches to recording data: • Linear recording • Helical recording 51
  • 52. Systems Architecture Chapter 5 Magnetic Storage 52
  • 53. Systems Architecture Chapter 5 Magnetic Storage 53
  • 54. Systems Architecture Chapter 5 Magnetic Storage 54
  • 55. Systems Architecture Chapter 5 Technology Focus Magnetic Tape Formats and Standards 55
  • 56. Systems Architecture Chapter 5 Magnetic Storage Magnetic Disk • Flat circular platters with metallic coatings that are rotated beneath read/write heads • Multiple platters can be mounted. • Once concentric circle is a track. • A fractional portion of a track is a cylinder. 56
  • 57. Systems Architecture Chapter 5 Magnetic Storage 57
  • 58. Systems Architecture Chapter 5 Magnetic Storage 58
  • 59. Systems Architecture Chapter 5 Magnetic Storage Magnetic Disk Types: • Hard Disk – magnetic disk media with a rigid metal base. • Floppy Disk (Diskette) – uses a base of flexible or rigid plastic material. 59
  • 60. Systems Architecture Chapter 5 Magnetic Storage Magnetic Disk Disk access time depends on several factor including: – Time required to switch among read/write heads – Time required to position the read/write heads – Rotational delay 60
  • 61. Systems Architecture Chapter 5 Technology Focus Whither the Floppy Disk 61
  • 62. Systems Architecture Chapter 5 Optical Mass Storage Devices • Advantages: – Higher recording density – Longer data life – Retain data for decades – Not subject to problems of magnetic decay and leakage 62
  • 63. Systems Architecture Chapter 5 Optical Mass Storage Devices • Optical storage devices store bit values as variations in light reflection. • Storage medium is a surface of highly reflective material. • The read mechanism consists of a low-power laser and a photoelectric cell. 63
  • 64. Systems Architecture Chapter 5 Optical Mass Storage Devices 64
  • 65. Systems Architecture Chapter 5 Optical Mass Storage Devices Optical Mass Storage Devices • CD-ROM • WORM (CD-R) • Magneto-optical • CD-RW • DVD 65
  • 66. Systems Architecture Chapter 5 Optical Mass Storage Devices 66
  • 67. Systems Architecture Chapter 5 Optical Mass Storage Devices CD-ROM • Originally developed for storing and distributing music (CD-DA). • Includes additional formatting to store the directory and file information. • Holds approximately 650 MB. 67
  • 68. Systems Architecture Chapter 5 Optical Mass Storage Devices WORM • Manufactured with all bit areas in a highly reflective state. • When a bit area is changed to low reflectivity, the process is irreversible. • Use high powered lasers to burn holes in the reflective layer. 68
  • 69. Systems Architecture Chapter 5 Optical Mass Storage Devices CD-R • Cheaper technology than WORM. • Use a laser that can be switched between high and low power. • Uses a laser-sensitive dye embedded in the CD-R disc. 69
  • 70. Systems Architecture Chapter 5 Optical Mass Storage Devices Magneto-Optical • Uses a laser and reflective light to sense bit values. • Applies a magnetic charge in a bit area. • The magnetic charge shifts the polarity of the reflected laser light. 70
  • 71. Systems Architecture Chapter 5 Optical Mass Storage Devices Phase-Change Optical Discs (CD-RW) • Allows optical storage media to be written non-destructively. • Based on materials that can change state easily. • The difference can be detected by newer optical scanning technologies. 71
  • 72. Systems Architecture Chapter 5 Summary • A typical computer system has primary and secondary storage devices. • The critical performance characteristics of primary storage devices are their access speed and the number of bits that can be accessed in a single read or write operation. 72
  • 73. Systems Architecture Chapter 5 Summary • Programs generally are created as through they occupied contiguous primary storage locations starting at the first location. • Magnetic storage storage devices store data bits as magnetic charges. • Optical discs store data bits as variations in light reflection. 73