So I have 2 VPS and I installed debian on both of them.

One VPS is using roughly 10mb right after the install, and the other is using 30mb. I'm just wondering why this is (both are minimal).

Did you perhaps install 32-bit Debian on one and 64-bit on the other?

Nope, they were both the same.

Ok so I just tried this out with a 32 bit and 64 bit install of Debian Lenny. Both took roughly the same amount of RAM with a fresh install, but I've seen the number a lot lower. Mine was around 30mb whereas I've seen it around 5mb. Why is this?

Look at the output of top (then hit F n) to see why. Also, http://www.linuxatemyram.com/.

Thanks for the link. So is there a way to tell exactly how much memory is actually being used?

Run the command "free" and read the numbers on the middle line (-/+ buffers/cache)

If that's true then I'm back to square one since those are the numbers I have been reading. Running that command in my tests showed some with 30mb used on a fresh install while others had only like 5mb.

yes, use top. hit F n to sort by memory use, then examine the top, say, 10 entries.

Although, top can be misleading, because it doesn't really give you the full story as far as shared memory among processes.

This script:
http://www.pixelbeat.org/scripts/ps_mem.py
attempts to do that. (I may have found out about it on this forum but I don't recall...)

Thanks, that tool seems pretty nifty. Is it possible though, that 2 fresh minimal installs of Debian 5 both take up significantly different amounts of RAM (ignoring the architecture)?

No.

Could just be the time factor -- maybe a cron job happened to kick in just before you looked at the ram usage on one of them, or there was some other relatively normal activity that lead to a bit of caching.

ps, htop and your logs should all help, if you want to see what actually happened (probably a bit late now though, unless you want to start the experiment all over again...).

Make sure you're using the same kernel on both.

Also, they're probably on different hosts, and different hosts may have different kernels and xen versions, which theoretically may influence RAM usage inside the VM.

Yeah, they are on different hosts. How would the kernel and xen make a difference in this? I do believe you, but I'm just curious as to why they matter.