Is this what happens?

say u have an Xp1800+

and windows xp

witha nice mobo

but u only use one stick of DDR thats 128

does the memory say wait! wait! hold on slow down i cant keep up

so does the memory slow down the whole systems overall performance

My guess (and it's only a guess) is that that would happen only when you are stressing your memory. I mean, how often are you going to saturate the bandwith of a memory chip? A game may do it if it's reading a lot of textures or whatever into RAM, but I wouldn't expect the bandwith to be saturated often. It's over one Gigabyte (gigabit?) per second!

The way I see it is that With a 2Ghz CPU, to saturate a 2GB/Sec chip, you would have to stuff 2 Bytes of stuff into RAM EACH AND EVERY CYCLE. And since most of the time you aren't sticking stuff into RAM, you should be OK.


But remeber, this is a guess... And my look at it could be killed if it is actually Gigabits/second.
JigPu

I've always been under the impression that windows will eat up as much ram as it can, so IMHO i would get more than 128, 256 i suggest or 512 if you can afford it, couldnt hurt!

Windows XP takes up a minimum of 75MB of RAM immediately after startup. The fact that you only have ~50MB left can be a real hindrance. It's not so much the RAM not trying as the fact that almost anything will fill it up, so you'll start writing to swap while playing Solitaire. =P

With 128MB of ram you will criple your machine. The problem is that you may not be running alot of programs where you can see them, but in the background there's alot of things load up when windows does. Especially if your system holds spyware, it can be the sole cripler of your ram. If you currently only have 128MB, i recommend getting 256MB, another 128MB will still barely only cut it with XP plus doing other things.

It's not really a bandwidth problem so much as a space problem. When your computer runs out of space to place programs into memory, it must us 'virtual' memory. This is a file on your Hard Drive that windows will use to store programs if it needs to. With memory, you'll get roughly 700-800MB/s transfer speeds, with a Hard Drive you will get about 50-70MB/s. This of course is all depending on your hardware, but these are soome rough estimates. As you can see, it really slows things down to have to use the page file.

If money's tight, 256MB should do, but if you got the extra money, go for 384, you won't regret it.

Cluster is right, to see whats going on with your ram just hit ctrl alt del, then click the performance tab and look at how much Physical Memory is being used and more importantly how much is available. It also gives you a graph which says PF usage (page file, which is what windows xp calls virtual memory), keep that graph on your screen and do stuff (open internet explorer or something) and watch how much it uses the page file(I have 256mb of ram and my pf is about 90mb). but as was already said you should really have at least 256mb.