Given yesterdays’s conflicting Photoshop test results, I rebooted my PowerMac Quad (with 8GB ECC memory), and re-ran the tests. I quit and restarted Photoshop CS2 each time. This time I also tested with History = 1, in part to give the MacBook Pro a chance of having enough memory. Here are the figures:
PowerMac Quad, History = 1, cache levels = 6: 49/49 seconds (3 runs) PowerMac Quad, History = 20, cache levels = 6: 80/85/88/90 seconds (4 runs) MacBook Pro, History = 1, cache levels = 6: 198/200/201 seconds (3 runs)
Using Photoshop’s History mechanism has a large impact. The variability using History=20 is disturbing, but no other programs were running, all sharing was off, and I didn’t even touch the mouse! Unfortunately, by not running Activity Monitor, it's impossible to see if any other system activity kicked in, but I heard no disk activity, and there were ample leftover CPU cycles.
I can’t explain yesterday’s slower timings other than a mistake (I’m not sure how), or that the system reboot fixed something. Still, I am unable to match the 38 second figure recorded by barefeats.com, although the figure with History=20 is only slightly higher than the barefeats History=20 result.