While trying to find information at the Adobe site about the
posterization problem I was experiencing with 16 bit/channel scans, I
happened upon some information I was totally unaware of regarding how
Photoshop uses scratch disk space. I have yet to read this information
anywhere else, and it might be very useful to people who scan or work
with larger files, a nd wish to improve Photoshop's speed and response.
This information was, as I recall, in the Windows section, so it might
not apply to Mac versions.
The references I read were in regard to both Photoshop 4 and 5, which
each work somewhat differently. In both versions, a scratch disk cannot
be over 2 gigs in size. That refers to one scratch disk. Photoshop 4
can have two scratch disks, while Photoshop 5 can have 4 scratch disks.
Now, here's where it gets interesting:
With Photoshop 4, as I stated above, each scratch disk can be no larger
than 2 gigs. You can have up to two scratch disks, but each must be in
a different partition or drive letter. So, you can allocate one to, say
Drive D and one to drive E, and each can be up to 2 gigs in size, if
there is that much space on the drive.
Of course, it helps if any scratch disk is on a drive partition which
has been defragmented, and also Adobe suggests that if you use a scratch
disk location which is the same partition as the Windows virtual memory,
then you should limit the size of the virtual disk, rather than keeping
it open to windows to decide, since Windows can (and will) use all the
space if it needs it, leaving nothing for Photoshop.
Now, here it gets more interesting. With Photoshop 5, you can assign
more than one scratch disk to each partition or drive number. Each
scratch disk can still only be 2 gigs in size. For instance, if you had
5 gigs free on one drive/partition (let's say drive D), you can assign
three scratch disks to Drive D. That will allow Photoshop to create a
primary one 2 gig scratch disk, another (secondary) 2 gig, and a 1 gig
scratch disk, adding up to 5 gigs, and you could still assign one more
for the forth, at another partition. Since Photoshop 5 allows for up to
4 scratch disks, you can assign up to 8 gigs for scratch disks (2 gigs
each) (as space allows).
I certainly didn't know any of this, so I'm going to make some changes
in my assignment. Hope this helps others as well.
Art
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