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SCSI

SCSI. Chapter 13. SCSI. Small Computer System Interface introduced in 1979 as a means of mass storage Common SCSI devices Hard drives - Scanners Tape backup units - CD-ROM drives Removable hard drives - Printers. SCSI.

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SCSI

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  1. SCSI Chapter 13

  2. SCSI Small Computer System Interface • introduced in 1979 as a means of mass storage • Common SCSI devices • Hard drives - Scanners • Tape backup units - CD-ROM drives • Removable hard drives - Printers

  3. SCSI • SCSI manifests itself through a SCSI chain, which is a series of SCSI devices working together through a host adapter • Host adapter attaches to the PC • picture on page 866

  4. SCSI Chains • All SCSI devices can de divided into 2 groups: external and internal • External devices stand alone and hooked to the external connector of the host adapter • Internal devices attach to the host adapter internally and the devices sit in the PC • SCSI has 50-pin, 68-pin, or 80-pin cables

  5. SCSI Chains • If the SCI cables are plugged in incorrectly, they can damage the devices • External devices all have 2 connections in the back, which enable you to daisy-chain • SCSI can have a maximum of 8 (the host plus 7 others) or 16 (host + 15) depending on the SCSI chain

  6. SCSI IDs • The values of the ID numbers range from 0 to 7, or 0 to 15 • No 2 devices can share the same ID number • Host adapter is usually set to 7 • Doesn’t matter what ID # other devices are set to • Try to use ID #0 for bootable hard drive • You can set SCSI IDs by setting jumpers

  7. SCSI chains • Each end of the chain must be terminated • examples of termination on page 877 • some devices self-terminate, but others you have to do yourself • usually set with jumpers; sometimes switches • can damage devices if terminating improperly

  8. SCSI Flavors • Types of SCSI: • SCSI - 1: 8-bit • SCSI - 2: 8-bit • SCSI - 2: 16-bit (wide) • SCSI - 2: 32-bit (wide) • SCSI - 3: numerous • Refer to chart on page 884 for types

  9. Bus mastering • Why is bus mastering an important part of SCSI? • devices that are on a SCSI chain can communicate with each other with very little use of the CPU, which frees up the system resources

  10. SCSI Cable and connectors • SCSI-1 & SCSI-2 (8-bit) used Type A: 50 pins • SCSI-2 (16-bit) used Type B: 68 pins • Some of the higher end SCSI-3 cables use 80 pins

  11. ASPI • Advanced SCSI programmer interface • mandates a standard way to write BIOS device drivers for SCSI devices • you can install a standardized set of device drivers for all your SCSI devices

  12. Compatibility with IDE • IDE and SCSI can both exist in one machine • IDE will get priority for the boot drive; you should use CMOS setup which allows SCSI to take priority • Not a good idea to mix them

  13. SCSI • SCSI adapters need an IRQ and usually take 3, so be careful with conflicts with COM ports. • Usually only happens with legacy PCs • Read the cost and benefits section on 893

  14. SCSI vs. IDE • SCSI used to be much bigger, now the advantage is disappearing • SCSI is much faster, uses bus mastering, and can support up to 15 devices now but also more expensive

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