This chapter describes data storage technologies used in computer systems. It discusses the characteristics of primary storage, such as RAM and ROM, and secondary storage devices, including magnetic tapes, disks, and optical discs. The key aspects covered are the memory hierarchy from fastest and most expensive to slower and cheaper, as well as the technologies behind magnetic and optical storage and how they encode data through magnetic charges or light reflection respectively.

1. Chapter 5
Data 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