Is there anybody know the interpretation of free memory information when you type sysinfo:/ to konqueror.

Total memory (RAM):  3,8 GB
  Free memory:  1,7 GB (+ 1,1 GB Caches)
  Free swap:  2,0 GB
Do I have 2.8GB free mem? If so, deoes it mean 1.1GB mem space has used with some apps but now they are closed;however they will be in the memory until some other apps write over that areas on the memory.

What is the command for console to get this info? When I write ps aux to the console it shows the percentages of memory usage of apps, instead of how much mem space they consume. Is there a way to also display it? Thanks.