First, let me start by saying:

• Assign Photoshop's ScratchDisk to a second HardDrive, a 10–30GB large, EMPTY dedicated volume.
  Yes, I am saying install a second hard drive and partition it.
• Running Photoshop's ScratchDisk on the boot system HardDrive will drag Mac's performance down — regardless if ScratchDisk is on a dedicated volume.
• ScratchDisk needs to be the fastest HardDrive we can configure....

My current work–station configuration:

• Mac G4, 2002 Quicksilver, dual 1000MHz, 1.5GB Ram.
• I use an Adaptec UL3D — dual channel Ultra 160 SCSI controller.
• My ScratchDisk — striped RAID 0 — is four, 18gb Atlas 10k IIs, two on channel A, two on channel B.
  RAID 0 partition #1 contains my 30GB dedicated ScratchDisk.
  RAID 0 partition #2 contains 25GB of work disk.
• A 36GB Seagate Cheetah 15K is my boot system and applications HardDrive.
  Partition #1 contains system 9.2.2
  Partition #2 contains system 10.2.4.
  

I have an 80GB Apple OEM, and a 120GB ATA — 7,200RPM Seagate Barracudas IV & V for data, storage, BackUp, video.

I can tell ya, this configuration runs Photoshop lickety-split!

+++++

Equipment recommendations:

Adaptec 39160: I have one (US$550) sitting on the shelf — I couldn't get it to work on system 10.2x, but it worked FLAWLESSLY on system 9x with SoftRaid drivers.

Check out SoftRaid.com for a wealth of RAID information (and the best 9x drivers around). SoftRaid web support is the fastest and best I've seen anywhere.

ATTO UL3D: ATTO.com cards are currently working here on system 9.2.2 and 10.2.4.
In fact, the RAID 0 volumes I created with ATTO ExpressRaid 2.8.1 are working SEAMLESSLY under 9.2.2/10.2.4 — both OSes can use the ATTO volumes!

10.2.8 broke my ATTO RAID 0:(
10.3.2, ATTO ExpressStripe2, 3.0 driver, 1.66f0, has NOT fixed it.
29FEB04: Just updated to ATTO ExpressStripe 2.1.1, 3.0.3 driver — maybe I'll try my SCSI RAID 0 again — XX....