Efficiency shows you how much Photoshop is using the scratch disk. Ideally this value is 100% (i.e. all work is being done in memory).
And I tried it out. I opened a 30 MB file with the following results
PS Memory setting 50% Efficiency 100%
PS Memory setting 70% Efficiency 100%
PS Memory setting 30% Efficiency 53%
In my last example I reserved less memory for Photoshop, only 30%.
I opened a 30MB file and Photoshop started to use the scratch disk, which caused the efficiency number to drop.
In most cases the efficiency should read 100% when you don't have any files open. That is understandable, since no scratch disk is in use, maybe created, but not in use.
If I had a 50% memory setting and a 200 MB file open, then my efficiency would have dropped too, since I have;
a) not enough memory reserved in Photoshop
or/and
b) just not enough memory available
I can't understand why you get those contradicting numbers. Like Erik said, must have to do with the lousy way that Windows 98 manages its memory, because these numbers really make no sense to me.
Important is that you test with the same file though.
