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Part 2 Computer Systems (Aux and I/O)

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Presentation on theme: "Part 2 Computer Systems (Aux and I/O)"— Presentation transcript:

1 Part 2 Computer Systems (Aux and I/O)
Hardware (Text No. 1 Chapter 2)

2 HARDWARE 2.4 Auxiliary storage devices
2.5 Input/output architecture and devices

3 Auxiliary Storage Devices
Types and characteristics of storage devices Main storage unit Auxiliary storage devices

4 Magnetic Tape

5 Magnetic Tape Type 0 Type 1 Original ferric-oxide tape
Very rarely seen these days Type 1 Standard ferric-oxide tape Also referred to as "normal bias"

6 Magnetic Tape Type 2 Type 4 "Chrome" or CrO2 tape
The ferric-oxide particles are mixed with chromium dioxide Type 4 "Metal" tape Metallic particles rather than metal-oxide particles are used in the tape

7 Magnetic Disk Unit Devices that store data using magnetic disks.
Most widely used auxiliary storage device Magnetic disks for personal computers or workstations are also called fixed disks or hard disks but the mechanism is the same.

8 Magnetic Disk Unit

9 Opening Up Hard Disk

10 Platters and Heads

11 Inside Hard Disk

12 Magnetic Media Tracks Data recorded along rings called ‘tracks’
Length of the outer tracks are larger than that of the inner tracks differ but: Storage capacity is the same Storage density increases from outer to inner

13 Magnetic Media

14 Magnetic Media Cylinders In magnetic disk units
Multiple magnetic disks Groups of tracks with the same radius on each of the disks is set as one data storage area called a ‘cylinder’ Makes for more efficient data retrieval Multiple fixed arm magnetic heads

15 Magnetic Media

16 Inside Hard disk

17 Magnetic Disk Structure

18 Magnetic Media Storage Capacity = storage capacity of 1 track *
number of tracks per cylinder * number of cylinders of the magnetic disk

19 Calculating Storage Capacity
Specifications Number of cylinders: 800 Number of tracks per cylinder: 19 Storage capacity per track: 20,000 bytes

20 Calculating Storage Capacity
Specifications Number of cylinders: 800 Number of tracks per cylinder: 19 Storage capacity per track: 20,000 bytes Calculations Storage capacity per cylinder 20,000 bytes * 19 tracks = 380,000 bytes/cylinder = app. 380KB Storage capacity of disk 380KB * 800 cylinders = 304,000 KB = app. 304 MB

21 Magnetic Disk Unit Recording Type Variable type
Data reading, writing performed on block basis. Read/write can be started from any track position Used in magnetic disks IBG = Inter-Block Gap

22 Calculating Storage Capacity (Blocking)
Calculate the number of cylinders required when 80,000 records of 200 bytes each are stored in a sequential access file of 10 records/block. Blocking cannot be extended over multiple tracks. Number of cylinders : 400 Number of tracks/cylinder : 19 Storage capacity/track : 20,000 bytes Inter-block gap (IBG) : 120 bytes

23 Calculating Storage Capacity (Blocking)
Number of blocks for the whole file = number of records/blocking factor 80,000 / 10 = 8,000 blocks Length of 1 block, including the IBG 200 bytes/record * 10 records/block bytes/block = 2,120 bytes/block Number of blocks on 1 track 20,000 bytes/track / 2,120 bytes/block = app blocks/track Because blocking cannot be extended over multiple tracks, floor(9.43) = 9 blocks/track Number of tracks for the whole file 8,000 blocks / 9 blocks/track = app tracks Ceil(888.88) = 889 tracks Number of cylinders required to write the whole file = number of tracks / number of tracks/cylinder 889 / 19 = app cylinders Ceil (46.78) = 47 cylinders.

24 Magnetic Media Structure and operation principles Sector type
Each track divided into approximately 20 small sectors. Reading/writing specified with sector number of selected track. Used in hard disks and floppy disks.

25 Magnetic Disk Structure

26 Magnetic Disk Parity check Defragmentation
Magnetic head reads/writes data to track bit by bit appending an extra bit for parity check. Defragmentation Data written on hard disks are not contiguous resulting in slow access time. Defragmentation will arrange data contiguously thereby speeding up read/write time

27 Magnetic Disk Access is the generic term for the act of reading specific data from the magnetic disk and writing it on a specific cylinder or track. Access time is calculated through the addition of the following: Seek time Search time Data transfer time

28 Magnetic Disk Seek time
Refers to the time a program or device takes to locate a particular piece of data. For disk drives, the terms seek time and access time are often used interchangeably. Technically speaking, however, the access time is often longer than seek time because it includes a brief latency period.

29 Magnetic Disk Search time or latency
Lapse of time until target data reaches the magnetic head position

30 Magnetic Disk Data transfer time
Time elapsed between when the magnetic head data access starts and when the transfer is completed

31 Access Time Access Time of Magnetic Disk Unit = Average Seek Time
+ Average Search Time + Data Transfer Time

32 Calculating Access Time
Specifications Capacity/track : 45,000 bytes Rotation speed : 2,500 rpm Average seek time : 10 s Find the access time (ms) for 15,000 bytes of data

33 Calculating Access Time
Calculation Average search time Revolution speed = 3,000 rpm 3,000 rev in 60 sec n(revolutions) in 1 second = 3000 / 60 = 50 rev/sec 1 rev in (1/50)sec = 0.02 sec/revolution = 20ms/rev Average search time = 20ms / 2 = 10ms

34 Calculating Access Time
Data Transfer Speed In 1 revolution, the information contained in 1 track passes through the magnetic disk head The disk makes 50 rev/sec Data transfer speed = 50 tracks/sec * 15,000 bytes/track = 750,000 = 750 * 103 bytes/sec Data transfer time for 9,000 bytes of data = (9*103)/(750*103) = sec = 12 ms Access Time = Average Seek Time + Average Search Time + Data Transfer Time 20ms + 10ms + 12ms = 42 ms

35 Floppy Disk Track – Concentric ring of data on a side of a disk.
Sector – A subset of a track, similar to wedge or a slice of pie.

36 Floppy Disk Recording method is sector type.
Within the outer protective casing is a circular flexible disk, hence “floppy” Low priced storage unit and easily transported, it is widely used.

37 Floppy Disk Structure

38 Floppy Disk Read/Write Located on both sides of a diskette
The heads are not directly opposite each other The same head is used for reading/writing, while a second wider head is used for erasing a track just prior to it being written.

39 Floppy Disk Stepper Motor
Makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position The read/write head assembly is fastened to the stepper motor shaft

40 Floppy Disk Storage capacity = Storage capacity per sector *
Number of sectors per track * Number of tracks per side * Number of sides (One side or both sides)

41 Calculating Floppy Disk Capacity
Specifications Sides available for use: 2 sides Track number/side: 80 tracks Sector number/track: 9 sectors Storage capacity/sector: 1,024 bytes Storage capacity of 1 track 1,024 bytes/sector  9 sectors/track = 9,216 bytes/track Storage capacity of 1 side is as follows: 9,216 bytes/track  80 tracks = 737,280 bytes = app. 737kB Both sides used: 737kB  2 = 1,474kB = app. 1.44MB

42 High Capacity Floppy Disks
100 MB or greater capacity Store large files such as graphics, audio, or video Used for backups SuperDisk drive Zip drive

43 Optical Disk (CD, DVD) Unit
Optical disk units Store/save image processing data of extremely large volume or as storage devices of large volume packaged software. These devices can store large volumes of data through a mechanism that reads out information using light reflection Widely used form of multimedia storage and distribution

44 CD-ROM Compact disc read-only memory
Can contain text, graphics, and video as well as sound Cannot be erased or modified Use CD-ROM drive or CD-ROM player to read Holds about MB Used to distribute software

45 Optical Disk (CD, DVD) Unit
Music (Audio) CD (CDA) CD-ROM CD-G (CD-Graphic) for image data CD-I (CD-Interactive) for interactive applications Photo-CD CD-R (CD-Recordable) CD-RW (CD-Rewritable) Multi-session

46 CD-ROM Structure

47 CD Surface

48 Reading from CD-ROM

49 CD-ROM Performance Seek time Transfer rate
Slow compared to magnetic disks due to heavy lens in the read head and the spiral structure Transfer rate Expressed in numeric values that represent how much data can be transferred in comparison with audio CDs. Audio CD player : 150kB/s CD-ROM units with transfer speeds 2 times or 3 times as fast as the transfer rate for audio CDs began to be developed and today the transfer rate has reached levels of 50x.

50 Optical Disk Specifications
Red Book Basic CD standard. Describes physical specifications of the CD Yellow Book Basic CDROM standard. Physical specifications of the CDROM Green Book Defines physical structure of CD-I (CD Interactive) Orange Book Defines physical structure of the CD-R (CD-Recordable)

51 DVD DVD (Digital Versatile Disk or Digital Video Disk)
Capable of storing up to 2 hours (or more, depending on standards used) of animated images and audio data Can be thought of as layering CD-ROMs one on top of the other

52 DVD Structure Uses MPEG2 compression technology Variations
High quality audio/video Variations DVD-ROM DVD-R DVD-RAM Regional encoding

53 DVD Surface

54 DVD Capacity Single layer single sided recording: 4.7 GB
Dual layer single sided recording: 8.5 GB Single layer dual sided recording: 9.4 GB Dual layer dual sided recording: 17 GB

55 CD versus DVD Specification CD DVD Track Pitch 1600 nanometers
Min Pit Length (Single layer) 830 nanometers 400 nanometers Min Pit Length (Double layer) NA 440 nanometers Note that double layer is only applicable to DVD.

56 Semiconductor Disk Unit
Storage unit of high speed and large capacity Uses flash memories and other devices Usually used in high-end mainframe computers as a storage unit positioned between the main storage unit and the auxiliary storage devices. Several G bytes of storage capacity Access time is 1/100th that of the magnetic disk unit

57 RAID High reliability and high performance of storage becoming increasingly important Especially in real-time networked environments Redundant Arrays of Inexpensive Disks Fault-tolerant Use from 2 to 32 disks in an array Most commonly used RAID 0, RAID 1 and RAID 5 Rapid data recovery (rollback) in the event of a disk failure Can be implemented in hardware which is the preferred method or software which is cheaper

58 RAID 0 Striping Data is stripped among all available disks
Between 2 and 32 disks are used. Fastest read/write No redundancy, hence no fault-tolerance One disk failure, all data in array are lost Useful for video production and editing, image editing, and any application requiring high bandwidth

59 RAID 1 Disk Mirroring/Duplexing
Uses 2 drives with same capacity where same content recorded on two hard disks concurrently Useful for critical mission applications Slowest of the RAID levels Fault tolerant - if one disk fails, data can be recovered from the other disk Single point of failure. If controller fails, both disks will be lost.

60 RAID 2 Hamming Code ECC Bit interleaved data is distributed over multiple hard disks with parity and error correction information No commercial implementations exist / not commercially viable

61 RAID 3 Bit interleaved data is distributed over multiple hard disks, and parity and error correction information stored on a dedicated hard disk Controller design is fairly complex Useful for video production and live streaming

62 RAID 4 Block (by sector) data is distributed over multiple hard disks, and parity and error correction information stored on a dedicated hard disk Difficult and inefficient data rebuild in the event of disk failure

63 RAID 5 RAID 5 (Striping with parity)
Most used for fault tolerance and speed Both block (by sector) data and parity and error correction information are distributed over multiple hard disks Most complex controller design Most commonly adopted in today's servers Uses between 3 to 32 disks

64 RAID 6 Also known as fault tolerant system
Hard disks form a matrix for row and column parity – faulty disk can be identified and replaced Very poor write performance

65 RAID 7 Heterogeneous system supports multiple hosts
One vendor (Storage Computer Corporation) proprietary solution Extremely high cost per MB

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