Computer Architecture - Hardware - Lessons 14 - SCSI - Eric Vanderburg
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The document discusses SCSI (Small Computer System Interface), which allows up to 15 devices to communicate simultaneously with the CPU through a SCSI host adapter. SCSI supports internal and external devices and uses LUNs (Logical Unit Numbers) to identify devices. It describes various SCSI types, standards, signaling methods, and connectors.
Computer Architecture - Hardware - Lessons 14 - SCSI - Eric Vanderburg
- 1. Computer Architecture: Core Hardware Chapter 14 SCSI Eric Vanderburg Eric Vanderburg – Core Hardware © 2005
- 2. SCSI • Small Computer System Interface • 15 devices on a controller • Internal & external devices • Multiple devices can communicate at the same time • Can talk to each other without utilizing the CPU. • SCSI host adapter is a layer between the CPU and the interface controller Eric Vanderburg – Core Hardware © 2005
- 3. SCSI • LUN (Logical Unit Number) – SCSI ID – Set using jumpers, drivers, or a dial on the back of the device • Host adapter – has highest number (7 or 15) – Uses DMA, IRQ, & I/O Address – SCAM (SCSI Configuration Auto- Matically) – allows PnP SCSI devices Eric Vanderburg – Core Hardware © 2005
- 4. Drivers • Requires disk to install windows • Some SCSI drivers are in the system BIOS Eric Vanderburg – Core Hardware © 2005
- 5. SCSI Types • Narrow SCSI – 8-bit data bus width – 50 pin cable (A Cable) • Wide SCSI – 16-bit data bus width – 68 pin cable (P Cable) Eric Vanderburg – Core Hardware © 2005
- 6. Drivers • ASPI (Advanced SCSI Programming Interface) – Created by Adaptec (major controller card mfg.) – WNASPI32.DLL, ASPI32.SYS – Provides direct support for most CD-ROM drives, changers and jukeboxes • CAM (Common Access Method) – ANSI – Can be used for several host adapters – Part of SCSI-3 Eric Vanderburg – Core Hardware © 2005
- 7. Signaling • Signaling is separate from the cable type and cannot be determined by looking at the cable. Be careful. • Single Ended (SE) – unbalanced signaling – one wire for voltage and another for grounding – Cheaper – Shorter cable lengths – Max speed: 20MHz Eric Vanderburg – Core Hardware © 2005
- 8. Signaling • Differential – balanced signaling – two cables with voltage (difference is used to get the signal) – Sends a signal to verify each bit (less errors) – More expensive – Longer cable lengths – HVD (High Voltage Differential) • cannot be mixed with SE devices because of voltage • Max speed: 40MHz – LVD (Low Voltage Differential) • has a compatible cable called LVD/SE that is shorter in length but supports both devices • Max speed: 320MHz Eric Vanderburg – Core Hardware © 2005
- 9. Connectors • 50 pin • 68 pin • 80 pin SCA – provides power to the device • Best case is to use 68 pin and then use converter to use 50 pin • Don’t forget the red stripe rule • Terminating Resistors – Can be a hardware terminator – Can be terminated at the controller through software or a jumper – On an end device through a switch or by applying a terminator to the device Eric Vanderburg – Core Hardware © 2005
- 10. Eric Vanderburg – Core Hardware © 2005 Connectors
- 11. SCSI Standards • SCSI 1 (Regular SCSI) – 8 bit only – Supports 7 devices & adapter – 5MBps • SCSI 2 (Fast SCSI) – 16 bit – Supports up to 15 devices – Mandatory parity checking – Up to 80MBps Eric Vanderburg – Core Hardware © 2005
- 12. SCSI Standards • SCSI 3 (Ultra SCSI) – 32 bit – Supports up to 32 devices – Supports SCAM – Ultra2 – 40MBps – Ultra3 – 80MBps – Ultra4 – 160MBps – Ultra5 – 320MBps **compare to SATA at 150Mbps • SAS (Serial Attached SCSI) – compatible with SATA Eric Vanderburg – Core Hardware © 2005
- 13. SCSI Summary • Generally more expensive • Faster & higher quality • Supports more devices • Many compatibility options Eric Vanderburg – Core Hardware © 2005