[frdmfghtr]

This isn't an iBook-centered question, it could apply to all Mac flavors (heck, probably even PCs too) but figures since I'm interested in the iBook application of it, I figured this was as good a place as any.

When determining how much RAM you should have as a minimum, lots of answers come back that are a metter of opinion..."more is better" or "enough to cover average use." While these answers are both true, they really vary from user to user.

Perhaps the nature of the question does vary with the user, but I'm looking to see if there is some sort of "benchmark" that can be used to determine the amount of RAM needed. One idea I had to determine if you have enough RAM is to look at page in/page out ratio. Right now, I have 1 GB in my 1.33 GHz 12" iBook G4, and the activity monitor shows a page out/page in ratio of 5305/300658, or a page out/page in ratio of 1.76%. Usually I'm sitting around 1% but I've been running some engineering mathematics software this morning which loves to gobble RAM and is the main reason I'm running 1 GB.

Before I added RAM, 512 MB gave me about a 10-11% page out/page in ratio.

Has anybody else heard of using such a measurement to determine if a system has sufficient RAM, and if so, is there a commonly used target ratio?

[ghporter]

It sounds like you've gone beyond merely deciding "more is better." But the page ratio doesn't tell the whole story. Do your apps respond more quickly with 1GB as compared to with 512MB? I'll bet you have found that while they have, they have not gotten to be twice as fast. This is because you still have to deal with the response speed of the hard drive.

iBooks (it really IS an iBook question now!) have notebook drives, almost always 4200 RPM drives. This slow rotational speed reduces drive system throughput, which can seriously affect the overall performance of applications.

The bottom line is that you can indeed max out RAM and not enjoy the effect you expect because of slower hard drive performance. On the other hand, if you were satisfied with the way things ran at 512MB of RAM, you should be REALLY happy with performance with 1GB, in spite of a lag in the hard drive access.

I'd recommend tying a paging metric with drive metrics to determine an optimum RAM size. We've been running with 640MB in our 800MHz G4 iBook for quite a while and it seems to be a very nice level for most applications.

[RadarBob2]

I think frdmfghtr is looking for some imperical formulation for determining RAM requirements. Optimally one could input parameters indicating use and - voila! "You need this much RAM..."

The flip side of this coin I think is the question "how much is too much RAM?" Well just let me say that when the entire OS, all files, everything on the hard drive fits into RAM all at once, then I have enough. But for us iBook users I think the question that matters is "what is the performance difference between a 512MB upgrade and a 1GB upgrade?" The individual has to decide if that increase is worth it for him or her. I think it boils down to a feeling of the difference, not a target number of some kind.

All I can say is that the 640MB I have is adequate for me. And I tend to keep lots of apps and utilities open. Perhaps as one gets more RAM (more than 256MB, less than ???) then other parts of the iBook becomes the performance bottleneck and more RAM beyond xxxxMB doesn't make a difference - for the iBook. This upper limit would be greater the higher performance the computer.

Finally, I think the page swap % frdmfghtr quoted gives some imperical indication of positive performance increase due to more RAM. Page swapping is OS work overhead that means the computer is pretending it has more memory than it really does. If it had all it wanted it would not do as much swapping. Oh, infinite RAM would not eliminate page swapping BTW.

P.S. I bought this iBook used and upgraded only 512MB because I will not be keeping it as long as I would if I had a brand new one. If I had a brand new iBook I would upgrade w/ 1GB because I *know* that I'd be avoiding another RAM upgrade 3.5 years from now.