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Computer Architecture CDROM Tape

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Computer Architecture CDROM+Tape ... – PowerPoint PPT presentation

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Title: Computer Architecture CDROM Tape


1
Computer Architecture CDROMTape
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  • ??????????????????????????
  • ??????????????????????

2
I/O Systems
interrupts
Processor
Cache
Memory - I/O Bus
Main Memory
I/O Controller
I/O Controller
I/O Controller
Graphics
Disk
Disk
Network
3
Optical Storage CD-ROM
  • Originally for audio
  • 650Mbytes giving over 70 minutes audio
  • Polycarbonate coated with highly reflective coat,
    usually aluminum
  • Data stored as pits
  • Read by reflecting laser
  • Constant packing density
  • Constant linear velocity

4
CD-ROM Drive Speeds
  • Audio is single speed
  • Constant linier velocity
  • 1.2 ms-1
  • Track (spiral) is 5.27km long
  • Gives 4391 seconds 73.2 minutes
  • Other speeds are quoted as multiples
  • e.g. 24x
  • The quoted figure is the maximum the drive can
    achieve

5
CD-ROM Format
Layered ECC
00
00
FF x 10
Mode
Sec
Data
Sector
Min
12 byte Sync
4 byte Id
2048 byte
288 byte
2352 byte
  • Mode 0blank data field
  • Mode 12048 byte dataerror correction
  • Mode 22336 byte data

6
Random Access on CD-ROM
  • Difficult
  • Move head to rough position
  • Set correct speed
  • Read address
  • Adjust to required location
  • (Yawn!)

7
CD-ROM for against
  • Large capacity (?)
  • Easy to mass produce
  • Removable
  • Robust
  • Expensive for small runs
  • Slow
  • Read only

8
Other Optical Storage
  • CD-Writable
  • WORM
  • Now affordable
  • Compatible with CD-ROM drives
  • CD-RW
  • Erasable
  • Getting cheaper
  • Mostly CD-ROM drive compatible

9
DVD - whats in a name?
  • Digital Video Disk
  • Used to indicate a player for movies
  • Only plays video disks
  • Digital Versatile Disk
  • Used to indicate a computer drive
  • Will read computer disks and play video disks
  • Dogs Veritable Dinner
  • Officially - nothing!!!

10
DVD - technology
  • Multi-layer
  • Very high capacity (4.7G per layer)
  • Full length movie on single disk
  • Using MPEG compression
  • Finally standardized (honest!)
  • Movies carry regional coding
  • Players only play correct region films
  • Can be fixed

11
DVD - Writable
  • Loads of trouble with standards
  • First generation DVD drives may not read first
    generation DVD-W disks
  • First generation DVD drives may not read CD-RW
    disks
  • Wait for it to settle down before buying!

12
Magnetic Tape
  • Serial access
  • Slow
  • Very cheap
  • Backup and archive

13
Digital Audio Tape (DAT)
  • Uses rotating head (like video)
  • High capacity on small tape
  • 4Gbyte uncompressed
  • 8Gbyte compressed
  • Backup of PC/network servers

14
Tape vs. Disk
  • Longitudinal tape uses same technology as
  • hard disk tracks its density improvements
  • Disk head flies above surface, tape head lies on
    surface
  • Disk fixed, tape removable
  • Inherent cost-performance based on geometries
  • fixed rotating platters with gaps
  • (random access, limited area, 1 media /
    reader)
  • vs.
  • removable long strips wound on spool
  • (sequential access, "unlimited" length,
    multiple / reader)
  • New technology trend
  • Helical Scan (VCR, Camcoder, DAT)
  • Spins head at angle to tape to improve
    density

15
Current Drawbacks to Tape
  • Tape wear out
  • Helical 100s of passes to 1000s for longitudinal
  • Head wear out
  • 2000 hours for helical
  • Both must be accounted for in economic /
    reliability model
  • Long rewind, eject, load, spin-up times not
    inherent, just no need in marketplace (so far)
  • Designed for archival

16
Summary
  • Disk industry growing rapidly, improves
  • bandwidth 40/yr ,
  • areal density 60/year, /MB faster?
  • queue controller seek rotate transfer
  • Advertised average seek time benchmark much
    greater than average seek time in practice
  • Response time vs. Bandwidth tradeoffs
  • Value of faster response time
  • 0.7sec off response saves 4.9 sec and 2.0 sec
    (70) total time per transaction gt greater
    productivity
  • everyone gets more done with faster response,
    but novice with fast response expert with slow
  • Processor Interface today peripheral processors,
    DMA, I/O bus, interrupts
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