Pata Device Classes - HP Evo D500 Reference Manual

Serial and Parallel ATA Drive Guidelines and Features
Any drive attached to a channel must have a drive designation. If only a single drive is connected
to a channel and its jumper is in the cable-select position, it is designated as the primary drive
(Drive/Device 0) by its attachment to the Drive/Device 0 cable position. If two cable-selected
drives are connected to a single channel, one will be designated by its attachment to the cable as
the primary (Drive/Device 0) and the other as secondary (Drive/Device 1).
For optimal performance of a computer system, all drives need to be attached to the ATA
channel in a specified sequence. This sequence is determined by the device class of the drives
and by specific attach sequence rules.

4.3.1 PATA Device Classes

In order to determine the best drive attach sequence, ATA/ATAPI drives are segregated into four
different classes based upon the bandwidth demands they place on an ATA channel. The most
demanding devices are in Class 1 and the least demanding are in Class 4.
Class 1
Hard
Drives
ATA-100
ATA-66
ATA-33
General Attach Guidelines
■
The lower the device class number, the faster the device and the more bandwidth required.
■
Drives installed in the Device 0 positions on both the primary and secondary channels
receive the greatest possible bandwidth.
■
The bootable ATA hard drive should always be installed on the primary channel in the
Device 0 position.
4–4
Class 2
High Speed
Optical Drives
DVD
DVD-CD R/W
336492-005
Class 3
Optical Storage
Drives
R/W CD-ROM
CD-ROM
Class 4
Magnetic
Storage Drives
LS-120
Tape
Zip
Service Reference Guide, d500