1. Chapter 5 Data Storage Technology

2. Chapter 5 Data Storage Technology
Chapter Outline
Storage Device Characteristics
Primary Storage Devices
CPU Memory Access
Magnetic Storage
Optical Mass Storage Devices

3. Chapter Goals
Describe the distinguishing characteristics of primary and secondary storage
Describe the devices used to implement primary storage
Describe memory allocation schemes
Compare and contrast secondary storage technology alternatives
Describe factors that determine storage device performance
Choose appropriate secondary storage technologies and devices

4. Data Storage Technology

5. Storage Device Characteristics
Breakdown Of Topics
Speed
Volatility
Access Methods
Serial Access
Random Access
Parallel Access
Portability
Cost and Capacity
Memory Storage Hierarchy

6. Storage Devices Consist of a read/write mechanism and a storage medium
Device controller provides interface
Primary storage devices
Support immediate execution of programs
Secondary storage devices
Provide long-term storage of programs and data

7. Primary and Secondary Storage Devices

8. Characteristics of Storage Devices
Speed
Volatility
Access method
Portability
Cost and capacity

9. Speed Primary Storage Typically much faster than secondary storage
Expressed in nanoseconds
billionths of a second = 10-6 second
Secondary Storage
Expressed in milliseconds
thousandths of a second = 10-3 second
Data Transfer Rate
= amount of data (bytes) / access time (seconds) = answer in “bytes per second”

10. Volatility Primary storage devices are usually volatile.
(Cannot reliably hold data for long periods of time)
Volatile memory requires constant power to maintain the stored information.
The most cost-effective primary storage technologies are volatile.
Non-volatile technologies have been widely used for primary storage in the past and may again be in the future.
Secondary storage devices are nonvolatile
(Holds data without loss over long periods of time)

11. Access Method Random Access (Direct Access)
any storage location can be accessed in the same amount of time
well suited for primary storage
Sequential Access
accessing a storage location takes a varying amount of time, depending on which storage location was accessed last
delays include
seek (position access device correctly)
cycle (wait for desired location in a revolving medium to appear at the access device)
Serial Access (Linear Access)

12. Portability Removable storage media with standardized formats
compact disc
tape storage
Typically results in slower access speeds

13. Cost and Capacity Cost increases:
With improved speed, volatility, or portability
As access method moves from serial to random to parallel access method
Primary storage is expensive
high speed and combination of parallel/random access methods
Capacity of secondary storage devices is greater than primary storage devices

14. Storage Device Characteristics and Their Relationship to Cost

15. Memory-Storage Hierarchy

16. Primary Storage Devices
Breakdown Of Topics
Storing Electrical Signals
Random Access Memory
Nonvolatile Memory
Memory Packaging

17. Primary Storage Devices
Critical performance characteristics
Access speed
Data transfer unit size
Must closely match CPU speed and word size to avoid wait states

18. Storing Electrical Signals
Directly
by devices such as batteries and capacitors
trade-off between access speed and volatility
Indirectly
write: use energy to alter the state of a device
read: an inverse process produces an equivalent electrical signal
Modern computers use memory implemented with semiconductors (RAM and NVM)

19. Random Access Memory Characteristics
Microchip implementation using semiconductors
Ability to read and write with equal speed
Random access to stored bytes, words, or larger data units
Basic types
Static RAM (SRAM) – uses transistors
Dynamic RAM (DRAM) – uses transistors and capacitors

20. The Cross-Coupled Gate
Time X Y Z ~Z t 1
t+1
Time X Y Z ~Z t 1
t+1

21. Bridging The Performance Gap Between Memory And Microprocessors
Random Access Memory
Bridging The Performance Gap
Between Memory And Microprocessors
Read-ahead memory access
Synchronous read operations
On-chip memory caches

22. Core Memory

23. Core Memory

24. Nonvolatile Memory
Random access memory with long-term or permanent data retention
Usually relegated to specialized roles and secondary storage; slower write speeds and limited number of rewrites
Generations of devices
ROM
EPROM
EEPROM
etc.

25. Nonvolatile Memory Flash RAM (most common NVM)
Competitive with DRAM in capacity and read performance
Relatively slow write speed
Limited number of write cycles
Based on EEPROM technology
NVM technologies under development
Ferroelectric RAM
Polymer memory

26. Memory Packaging Dual in-line packages (DIPs)
Early RAM and ROM circuits
Single in-line memory module (SIMM)
Standard RAM package in late 1980s
Double in-line memory module (DIMM)
Newer packaging standard
A SIMM with independent electrical contacts on both sides of the module

27. Memory Packaging

28. Memory Packaging SIMM memory module DIMM memory module
SODIMM memory module

29. Memory Packaging

30. CPU Memory Access Breakdown Of Topics Physical Memory Organization
Memory Allocation and Addressing

31. CPU Memory Access
Critical design issues for primary storage devices and processors
Physical organization of memory
Organization of programs and data within memory
Method(s) of referencing specific memory locations

32. Physical Memory Organization
Actual number of memory bytes that physically are installed in the machine
Most and least significant bytes
Big endian and little endian
Addressable memory
Highest numbered storage byte that can be represented

33. A Linear Address Space

34. Memory Allocation and Addressing
Assignment of specific memory addresses to system software, application programs, and data
Absolute addressing
Indirect addressing (relative addressing)
Offset register

35. Memory Allocation A Simple Scheme

36. Memory Allocation for Multiple Programs

37. Memory-Storage Hierarchy

38. Magnetic Storage Exploits duality of magnetism and electricity
Converts electrical signals into magnetic charges
Captures magnetic charge on a storage medium
Later regenerates electrical current from stored magnetic charge
Polarity of magnetic charge represents bit values zero and one

39. Principles of Magnetic Storage

40. Data Loss in Magnetic Storage

41. Areal Density

42. Magnetic Tape
Ribbon of plastic with a coercible (usually metallic oxide) surface coating
Mounts in a tape drive for reading and writing
Relatively slow serial access
Compounds magnetic leakage; wraps upon itself
Susceptible to stretching, friction, temperature variations

43. Cassette or Cartridge Magnetic Tape

44. Magnetic Tape Two approaches to recording data Linear recording
Helical scanning
Several formats and standards
DDS [DAT]
AIT
Mammoth
DLT
LTO
etc.

45. Parallel Tracks vs. Helical Scanning

46. Technology Focus Quarter Inch Committee (QIC)
Format
Year
Cartridge Size (Inches)
Capacity (GB)
Tracks
Recording Density
(bpi)
QIC-80
1988
4 x 6
.08 28
14,700
QIC-120
1991
0.125 15
10,000
QIC-525
1992
0.525 26
20,000
QIC-2100
1993
2.1 30
50,800
QIC-3095
1995
3.25 x 2.5 4 72
67,733
QIC-3220
1997 10
108
106,400

47. Magnetic Disk
Flat, circular platter with metallic coating that is rotated beneath read/write heads
Random access device; read/write head can be moved to any location on the platter
Hard disks and floppy disks
Cost performance leader for general-purpose on-line secondary storage

48. Components of a Magnetic Disk Drive

49. Track and Sector Organization on a Disk Platter Surface

50. Magnetic Disk Access Time
Head-to-head switching time
Track-to-track seek time
Rotational delay
Most important performance numbers
Average access time
Sequential access time
Sustained data transfer rate

51. Hard Disk Drive Performance Statistics is most strongly affected by
Average Access Time
is most strongly affected by
Rotational Speed

52. Track Zones

53. Optical Mass Storage Devices
Store bit values as variations in light reflection
Higher areal density and longer data life than magnetic storage
Standardized and relatively inexpensive
Uses
read-only storage with low performance requirements
applications requiring high capacity, portability, and a standardized format

54. Optical Disc Read Operations
One Bit
Zero Bit

55. Optical and Magneto-optical Storage Technology

56. CD-ROM
Read-only; data permanently embedded in durable polycarbonate disc
Bit values represented as flat areas (lands) and concave dents (pits) in the reflective layer
Data recorded in single continuous track that spirals outward from center of disc
Popular medium for distributing software and large data sets

57. CD-ROM Advantages Drawbacks Standardized format High density
Cheap to manufacture
Cannot be rewritten
Capacity limited to 700 MB

58. CD-R
Uses a laser that can be switched between high and low power and a laser-sensitive dye embedded in the disc
Relatively cheap
Common uses
create music CDs on home computers
back up data from other storage devices
create archives of large data sets
manufacture small quantities of identical CDs

59. Magneto-Optical Uses a laser and reflected light to sense bit values
Technology peaked in the mid 1990s
Advantages over CD-RW
faster access speed
higher capacity

60. Phase-Change Optical Discs
Enables nondestructive writing to optical storage media
Materials change state easily from non-crystalline (amorphous), to crystalline, and then back again
Reflective layer is a compound of tellurium, selenium, and tin
Example: CD-RW

61. DVD Improves on CD and CD-RW technology
Increased track and bit density: smaller wavelength lasers and more precise mechanical control
Improved error correction
Multiple recording sites and layers

62. Summary Storage devices and their underlying technologies
Characteristics common to all storage devices
Technology, strengths, and weaknesses of primary and secondary storage

63. Chapter Goals
Describe the distinguishing characteristics of primary and secondary storage
Describe the devices used to implement primary storage
Describe memory allocation schemes
Compare and contrast secondary storage technology alternatives
Describe factors that determine storage device performance
Choose appropriate secondary storage technologies and devices