Device Classes; Attach Sequence Rules By Class Priority - HP Compaq dx2000 ST Series Reference Manual

4.3.1 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 controller. 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 controllers
receive the greatest possible bandwidth.
The bootable ATA hard drive should always be installed on the primary controller in the
Device 0 position.

4.3.2 Attach Sequence Rules by Class Priority

Drives should be attached in the sequence shown for optimum performance starting at
position 1.
*If there are three or more devices, two or more of which are hard drives, two hard drives should
be attached to the primary controller first before following the General Attach Sequence Rule.
Service Reference Guide, dx2000 ST
Class 2
High Speed
Optical Drives
DVD
DVD-CD R/W
4
3
Primary
Controller*
Secondary
Controller
371411-001
Ultra ATA Drive Guidelines and Features
Class 3
Optical Storage
Drives
R/W CD-ROM
CD-ROM
1
2
4
3
Device 1 Device 0
Class 4
Magnetic
Storage Drives
LS-120
Tape
Zip
1
2
4–3