Chapter 22

1. Chapter 22 All About SCSI

2. SCSI Basics • Standard for communication between subsystem of peripheral devices and system bus • Bus can contain/be used by up to 7 or 15 devices • Bus requires controller embedded on motherboard or host adapter inserted into an expansion slot • Faster, more expensive, more difficult to install than similar IDE devices • Mostly used in corporate settings A+ Guide to Managing and Maintaining Your PC, Fifth Edition

3. The SCSI Subsystem • Enables two devices on SCSI bus to pass data between them without going through CPU • Requires SCSI controller and unique SCSI IDs assigned to each device, including host adapter • Components • Host adapters • Device drivers A+ Guide to Managing and Maintaining Your PC, Fifth Edition

4. SCSI Host Adapter A+ Guide to Managing and Maintaining Your PC, Fifth Edition

5. IDE versus SCSI Bus Communication A+ Guide to Managing and Maintaining Your PC, Fifth Edition

6. Host Adapters • Manage all devices on SCSI bus • Support internal and external SCSI devices • Form a single daisy chain with devices A+ Guide to Managing and Maintaining Your PC, Fifth Edition

7. Bus Mastering • Bus master attached to PCI bus can access memory and other devices without accessing the CPU • SCSI host adapter does not require a DMA channel A+ Guide to Managing and Maintaining Your PC, Fifth Edition

8. SCAM-Compliant • Can assign SCSI IDs dynamically at startup • Two levels • Level 1 requires that the devices – but not the host adapter – be assigned an ID at startup by software • Level 2 requires that the host adapter – as well as the devices – be assigned an ID at startup by software A+ Guide to Managing and Maintaining Your PC, Fifth Edition

9. SCSI Device Drivers • Enable OS to communicate with a host adapter • Two popular types • ASPI (Advanced SCSI Programming Interface) – more popular of the two • CAM (Common Access Method) A+ Guide to Managing and Maintaining Your PC, Fifth Edition

10. Variations in SCSI • Bus width • Signaling methods used on SCSI cables • Connectors used with SCSI cables • Termination • SCSI-1, SCSI-2, and SCSI-3 A+ Guide to Managing and Maintaining Your PC, Fifth Edition

11. Bus Width • Narrow SCSI • 8-bit data path • Uses a cable with a 50-pin connector (A cable) • Wide SCSI • 16-bit data path • Uses a cable with a 68-pin connector (P cable) A+ Guide to Managing and Maintaining Your PC, Fifth Edition

12. Signaling Methods Used on SCSI Cables A+ Guide to Managing and Maintaining Your PC, Fifth Edition

13. Signaling Methods Used on SCSI Cables (continued) A+ Guide to Managing and Maintaining Your PC, Fifth Edition

14. Connectors Used with SCSI Cables • Not affected by signaling method used • Types vary in shape and pin density; can be connected with adapters • Two main types: • 50-pin (A cable) • 68-pin (P cable) • Last connector on last device must be filled with a terminator A+ Guide to Managing and Maintaining Your PC, Fifth Edition

15. SCSI Connectors A+ Guide to Managing and Maintaining Your PC, Fifth Edition

16. Multiple Connectors on the SCSI Bus A+ Guide to Managing and Maintaining Your PC, Fifth Edition

17. Termination • Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain • Required at each end of a SCSI chain A+ Guide to Managing and Maintaining Your PC, Fifth Edition

18. Ways to Terminate the End of a SCSI Chain • Switch setting on host adapter that activates or deactivates a terminating resistor on the card • Single SCSI connection or two connections • Resistor physically mounted on the device • Internal terminators that turn on or off with a jumper setting on the device • Software-controlled termination A+ Guide to Managing and Maintaining Your PC, Fifth Edition

19. External SCSI Terminator A+ Guide to Managing and Maintaining Your PC, Fifth Edition

20. SCSI-1 (Regular SCSI) No common command set 8-bit data bus 7 possible devices SCSI-2 (Fast SCSI) Common command set 16-bit data bus 15 possible devices Mandatory parity checking Major Versions of SCSI A+ Guide to Managing and Maintaining Your PC, Fifth Edition

21. Major Versions of SCSI (continued) • SCSI-3 (Ultra SCSI) • Supports both parallel and serial data transmission, and FireWire connections • Data transfer of 320 MB/sec (Ultra 320 SCSI) • Support up to 32 devices • Includes SPI standard A+ Guide to Managing and Maintaining Your PC, Fifth Edition

22. Comparing IDE and SCSI • IDE • May give better performance when using a single disk drive with an OS like Windows 98 or Windows Me • SCSI • Increases performance where heavy load is placed on system and its components • Some OSs include increased support for SCSI features and take better advantage of them • More expensive; better performance A+ Guide to Managing and Maintaining Your PC, Fifth Edition

23. Considerations When Choosing Between IDE and SCSI Drives A+ Guide to Managing and Maintaining Your PC, Fifth Edition

24. More SCSI Considerations • Drives perform better in RAID array • Generally provides better performance • Often used on high-demand servers A+ Guide to Managing and Maintaining Your PC, Fifth Edition

25. Installing a SCSI Hard Drive • Host adapter and cables must be compatible with SCSI drive • Configure SCSI host adapter and SCSI hard drive to communicate with each other: • Set SCSI IDs • Disable/enable disk drive and hard drive controllers • Check terminating resistors • Run CMOS setup for a SCSI system • Load SCSI device drivers A+ Guide to Managing and Maintaining Your PC, Fifth Edition

26. SCSI Hard Drives Connectors A+ Guide to Managing and Maintaining Your PC, Fifth Edition

27. Hands-on Project: Install a SCSI Device • pp. 1021 A+ Guide to Managing and Maintaining Your PC, Fifth Edition