A+ Guide to Managing and Maintaining Your PC Fifth Edition Chapter 22 All About SCSI

2 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

3 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

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

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

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

7 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

8 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

9 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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)

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

11 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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)

12 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

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

14 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

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

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

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

18 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

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

20 A+ Guide to Managing and Maintaining Your PC, Fifth Edition Major Versions of SCSI 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

21 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

22 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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

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

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

25 A+ Guide to Managing and Maintaining Your PC, Fifth Edition 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: 1.Set SCSI IDs 2.Disable/enable disk drive and hard drive controllers 3.Check terminating resistors 4.Run CMOS setup for a SCSI system 5.Load SCSI device drivers

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

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