1. Chapter 22
All About SCSI

2. You Will Learn…
About basics of SCSI (Small Computer System Interface) technology and components
How SCSI hard drives compare to IDE drives
How to install a SCSI device
Troubleshooting tips for SCSI

3. 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, depending on SCSI standard
Bus controller can be either:
An expansion card (host adapter)
Embedded on motherboard

4. The SCSI Subsystem Host adapter
Gateway from the SCSI bus to the system bus
Card inserted onto expansion slot on mother board
Manages all devices on SCSI bus
Supports internal and external SCSI devices
Forms a single daisy chain with devices
Two devices on SCSI bus can pass data between them without going through CPU; convenient for back up

5. The SCSI Subsystem

6. IDE vs. SCSI Bus Communication

7. The SCSI Subsystem
SCSI drive has its controller mounted inside the drive housing and can have a variable number of sectors per track
Each end of the SCSI chain has a terminating resistor
Each device on the bus is assigned a SCSI ID
Two important components
Host adapters
Device drivers

8. Host Adapters Issues to consider when selecting a host adapter BIOS
Expansion slot
Bus mastering

9. BIOS
Look for a host adapter that is PnP compatible and has a configuration utility built into its ROM
Check for software that configures termination and assigns system resources
Look for a host adapter whose BIOS can configure SCSI devices using the bus controlled by the adapter
See how many devices the BIOS supports (up to 15 is best)

10. Expansion Slot
Host adapter must fit the expansion slot you plan to use
Choose 32-bit PCI bus for faster data transfer rate (Pentium motherboard)

11. Bus Mastering
Choose a host adapter that supports bus mastering, if your system bus supports it

12. SCAM-Compliant SCAM = SCSI Configuration AutoMatically
Method by which SCSI devices and the host adapter can be PnP compliant
Two levels (Level 1 and Level2)

13. Vendors for SCSI Host Adapters

14. SCSI Device Drivers Enable OS to communicate with a host adapter
Two popular driver types
ASPI (Advanced SCSI Programming Interface) – more popular of the two
CAM (Common Access Method)

15. Variations in SCSI
Standards
Types of cabling
Bus widths

16. Bus Width
Narrow SCSI (8 bits)
Wide SCSI (16 bits)

17. SCSI Cables Signaling Methods

18. Single-Ended Signaling
Send a signal on a pair of twisted wires; one carries voltage, the other is a ground
Less expensive, but maximum cable length cannot be as long because data integrity is not as great

19. Differential Signaling
Send a signal on a pair of twisted wires; both carry voltage, and the signal is calculated to be the difference between the two voltages
Better signal accuracy
Greater reliability and reduction in chance of data errors
High Voltage Differential (HVD)
Low Voltage Differential (LVD)

20. SCSI Cables

21. Signaling Symbols

22. SCSI Cable Connectors

23. SCSI Cable Connectors

24. Termination
Provides an echo effect from electrical noise and reflected data at the end of the SCSI daisy chain

25. Ways to Terminate a SCSI Chain
Host adapter can have a switch setting that activates or deactivates a terminating resistor on the card
Device can have either a single SCSI connection or two connections (external terminator)
Device at end of the chain can be terminated by a resistor physically mounted on that device
Internal terminator
Controlled by software

26. Types of Terminators Passive terminators Active terminators
Forced perfect terminators (FPTs)

27. Major Versions of SCSI SCSI-1 = Regular SCSI SCSI-2 = Fast SCSI
8-bit data bus
7 possible devices
SCSI-2 = Fast SCSI
Common command set
16-bit data bus
15 possible devices
Mandatory parity checking
SCSI-3 = Ultra SCSI
Supports both parallel and serial data transmission
Supports FireWire connections
Data transfer of 320 MB/sec
SPI (SCSI Parallel Interface) standards

28. SCSI Standards

29. SCSI Cable Specifications

30. Comparing IDE and SCSI
IDE supports only four internal devices; SCSI supports both internal and external and allows you to add more
SCSI devices are generally of higher quality than IDE devices and more expensive
IDE devices require separate IRQ for each device; SCSI requires only one for entire chain
continued…

31. Comparing IDE and SCSI Both are generally backward-compatible
SCSI hard drive with supporting host adapter and cable costs more than an IDE hard drive
SCSI subsystem provides faster data transfer than an IDE drive
SCSI generally provides better performance than IDE; often used on high-demand servers
continued…

32. Comparing IDE and SCSI
Good host SCSI host adapter allows connection of other SCSI devices to it
With SCSI, two or more devices can operate simultaneously; with IDE, only one IDE drive on an IDE channel can be busy at a time

33. Basic Steps for SCSI Installation
Set jumpers or switches on host adapter and install it on motherboard; install host adapter drivers
Use jumpers or switches to assign SCSI ID
Attach cabling to host adapter and each device
Verify termination at both ends of daisy chain
Power up one device at a time
Install drivers and software

34. Installing a Host Adapter Card
Install card in expansion slot
Change/verify default settings using setup program
Verify settings under Advanced Configuration Options
Windows supports host adapter; it loads device drivers automatically and installs host adapter
Use Device Manager to verify correct installation of host adapter
Install external SCSI device

35. Installing a Host Adapter Card

36. Installing a Host Adapter Card

37. Setting Device IDs During Installation
With SCAM-compliance, SCSI IDs are assigned automatically
Without SCAM compliance, set device SCSI IDs manually
Each ID must be unique; no two devices on same SCSI channel can have same ID number
For narrow SCSI, use IDs 0-7
For wide SCSI, use IDs 0-15
Host adapter usually has ID 7

38. Setting Device IDs During Installation
To set IDs for external devices, use either push-button selector or rotary selector
To set IDs for internal devices, use set of jumpers on the device

39. Setting External Device IDs

40. Setting Internal Device IDs

41. Installing a SCSI Hard Drive
Make sure host adapter and cables are compatible with SCSI drive
Configure SCSI host adapter and SCSI hard drive so they can communicate with each other as follows:
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

42. General Troubleshooting Tips
Keep notes and read documentation
Add one SCSI device at a time
Use good quality components
Limit cable length

43. Troubleshooting Installation Problems
Turn on external devices first, then computer
Check connections
Verify correct termination (common cause of problems)
Verify most updated BIOS
Install PCI host adapter in PCI bus that supports bus mastering

44. Troubleshooting Booting Problems
Confirm BIOS setup drive configuration is set to “No Drives Installed”
Verify that SCSI drive is partitioned, has a primary partition, and boot partition is set as active
Back up SCSI hard drive and do low-level format on it

45. Chapter Summary
How SCSI technology works to provide better performance and greater expansion capabilities for many internal and external devices (hard drives, CD-ROM drives, DVD drives, and scanners)
Faster, more expensive, more difficult to install than similar IDE devices
Advantages and disadvantages of SCSI