UNIX for Dummies Questions & Answers

I have 512 mem on this laptop, though 'top' tells me I only have 380. However, Ubuntu is using 288 mb of memory, when I only have 3 terminals, running lynx, vim(for this file) and (of course) top. Considering it I have lynx running a 600 page txt file, which of course would eat some memory but 300? And even worse when i start X. Let's try it. First I reboot since she's been up a couple of hours.

Before X is launched:

Mem: 385812k total, 178516k used, 207296k free, 8700k buffered

Staring at the buffered memory for one minute it's now increased to 8852.
Used mem has also increased to 178888. 300 k on two lines.
(That's probably the two most expensive ascii-lines I've ever seen.)

After X is launched: (mem already at: used: 179260 and buff: 9388)

Mem: 385812k total, 264612k used, 121200k free, 13604k buffered
That's about 80 meg. Starting timer.
13:12:30 (with the above memory)

13:17:30 (five minutes later)
Mem: 385812k total, 265356k used, 120456k free, 14144k buffered

That's another 5 meg memory used. For just staring at the 'top' program.
In two hours I'll run out of memory! What's happening behind the scenes?

Before i rebooted I checked my free memory after starting X.
It went down to 35 meg. It'd been up for 3-3.5 hours running a 600+ page txt file in lynx.

Regards
Richard

(Mem is now (13:27:00) used: 266852 free: 118960 buff: 15220
A lot less in ten minutes than in five... Hmmm...)