UPGRADING REPAIRING PCs
UPGRADING REPAIRING PCs
UPGRADING REPAIRING PCs
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
114<br />
Note<br />
Chapter 4—SCSI and IDE Hard Drives and Optical Drives<br />
The A cable is the standard 50-pin SCSI cable, whereas the P<br />
cable is a 68-pin cable designed for 16-bit. Maximum cable<br />
length is 6 meters (about 20 feet) for standard speed SCSI, and<br />
only 3 meters (about 10 feet) for Fast/Fast-20/Fast-40 (Ultra)<br />
SCSI. Ultra2Wide allows cable lengths up to 12 meters (about<br />
40 feet!).<br />
Single-Ended Versus Differential<br />
SCSI<br />
SCSI is not only a flexible interface, it’s also a multi-platform interface.<br />
Traditionally, <strong>PCs</strong> have used single-ended SCSI, whereas other<br />
platforms use differential SCSI. Because these two types of SCSI are<br />
not interchangeable, you should never mix them on a host adapter<br />
designed for single-ended SCSI. Use the markings in Figure 4.6 to<br />
distinguish between these.<br />
SCSI SE SCSI LVD<br />
Single-Ended<br />
SCSI Devices<br />
SCSI LVD/SE SCSI DIFF<br />
Low-Voltage<br />
Differential/Single-Ended<br />
Multi-mode SCSI<br />
Figure 4.6 Single-ended and differential SCSI universal symbols.<br />
Low-Voltage Differential Devices<br />
Low-Voltage<br />
Differential<br />
SCSI<br />
High-Voltage<br />
Differential<br />
SCSI<br />
Ultra2Wide SCSI devices, which run at 80MB/sec maximum transfer<br />
rates, use a modified version of differential SCSI called low-voltage<br />
differential (LVD). Workstation-oriented cards, such as Adaptec’s<br />
AHA-2940U2W, enable the use of LVD Ultra2Wide devices and
Change language