1. 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

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

4. SCSI Host Adapter

5. IDE versus SCSI Bus Communication

6. Host Adapters Manage all devices on SCSI bus
Support internal and external SCSI devices
Form a single daisy chain with devices

7. Variations in SCSI Bus width Signaling methods used on SCSI cables
Connectors used with SCSI cables
Termination
SCSI-1, SCSI-2, and SCSI-3

8. Bus Width Narrow SCSI Wide 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)

9. Signaling Methods Used on SCSI Cables
Single-ended (SE)
Differential
Send signal on pair of twisted wires – one carries voltage, one is a ground
Less expensive than differential
Shorter maximum cable length; data integrity is not as great
Send signal on pair of twisted wires – both carry voltage; signal calculated to be the difference between the two
Better signal accuracy and greater reliability
HVD and LVD

10. Signaling Methods Used on SCSI Cables (continued)

11. SCSI Cables

12. 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)

13. SCSI Connectors

14. Multiple Connectors on the SCSI Bus

15. Termination
Prevents echo effect from electrical noise and reflected data at end of SCSI daisy chain
Required at each end of a SCSI chain

16. External SCSI Terminator

17. Major Versions of SCSI SCSI-1 (Regular SCSI) 50 pin cable
8-bit data bus
7 possible devices
5MHz sync and async operations
SCSI-2 (Fast SCSI)
50 pin cable High density. Fast SCSI(10MHz)
16-bit data bus
15 possible devices
Mandatory parity checking

18. Major Versions of SCSI (continued)
SCSI-3 (Ultra SCSI)
Supports both parallel and serial data transmission
Supports FireWire connections
Data transfer of 320 MB/sec
Includes SPI standard

19. SCIS Standards

20. SCIS Standards (continued)

21. SCIS Standard Cable Specs

22. Considerations When Choosing Between IDE and SCSI Drives
IDE supports only four internal devices
Supports internal and external devices; allows additional ones
Separate IRQ required for each device
Only one IRQ required for entire chain
Generally backward-compatible
Only one IDE drive on an IDE channel can be busy at a time
Two or more devices can operate simultaneously

23. SCSI Hard Drives Connectors