1 Chapter 5 Data Storage Technology

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

3 Systems Architecture Chapter 5 Chapter Goals Describe factors that determine storage device performance Choose appropriate secondary storage technologies and devices

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

5 Systems Architecture Chapter 5 Storage Device Characteristics

6 Systems Architecture Chapter 5 Storage Device Characteristics Speed Volatility Access method Portability Cost and capacity

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 10 5 or more.

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.

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.

10 Systems Architecture Chapter 5 Storage Device Characteristics Volatility Primary storage devices are generally volatile. Secondary storage devices are generally non-volatile.

11 Systems Architecture Chapter 5 Storage Device Characteristics Access Method –Serial Access –Random Access –Parallel Access

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)

13 Systems Architecture Chapter 5 Storage Device Characteristics Parallel Access – a device that is capable of simultaneously accessing multiple storage locations. (Random Access Memory)

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.

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.

16 Systems Architecture Chapter 5 Storage Device Characteristics

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.

18 Systems Architecture Chapter 5 Storage Device Characteristics

19 Systems Architecture Chapter 5 Primary Storage Devices Storing Electrical Signals Random Access Memory Read-Only Memory Memory Packaging

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.

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

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

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.

24 Systems Architecture Chapter 5 Primary Storage Devices

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.

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.

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.

28 Systems Architecture Chapter 5 Primary Storage Devices Read-Only Memory Electronically Erasable Programmable Read- Only Memory (EEPROM) Flash Memory

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.

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.

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)

32 Systems Architecture Chapter 5 Primary Storage Devices

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.

34 Systems Architecture Chapter 5 CPU Memory Access Physical Memory Organization Memory Allocation and Addressing

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.

36 Systems Architecture Chapter 5 Physical Storage Devices

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.

38 Systems Architecture Chapter 5 Memory Allocation and Addressing

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.

40 Systems Architecture Chapter 5 Memory Allocation and Addressing

41 Systems Architecture Chapter 5 Memory Allocation and Addressing

42 Systems Architecture Chapter 5 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.

43 Systems Architecture Chapter 5 Magnetic Storage

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

45 Systems Architecture Chapter 5 Magnetic Storage

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.

47 Systems Architecture Chapter 5 Magnetic Storage Storage Density

48 Systems Architecture Chapter 5 Magnetic Storage Magnetic Integrity Depends on the nature of the storage medium’s construction and the environmental factors.

49 Systems Architecture Chapter 5 Magnetic Storage Magnetic Storage Devices: Magnetic Tape Magnetic Disk

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.

51 Systems Architecture Chapter 5 Magnetic Storage Magnetic Tape Approaches to recording data: Linear recording Helical recording

52 Systems Architecture Chapter 5 Magnetic Storage

53 Systems Architecture Chapter 5 Magnetic Storage

54 Systems Architecture Chapter 5 Magnetic Storage

55 Systems Architecture Chapter 5 Technology Focus Magnetic Tape Formats and Standards

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.

57 Systems Architecture Chapter 5 Magnetic Storage

58 Systems Architecture Chapter 5 Magnetic Storage

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.

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

61 Systems Architecture Chapter 5 Technology Focus Whither the Floppy Disk

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

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.

64 Systems Architecture Chapter 5 Optical Mass Storage Devices

65 Systems Architecture Chapter 5 Optical Mass Storage Devices CD-ROM WORM (CD-R) Magneto-optical CD-RW DVD

66 Systems Architecture Chapter 5 Optical Mass Storage Devices

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.

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.

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.

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.

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.

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.

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.