As all of you know, N900 has 32 gb of internal memory. But when i go to the file manager and go to the memory status, it says that i only have 27 gb and 23 gb available. What's wrong?

It is called "creative marketing"

Well, 32 GB is not the same as 32 GiB.
Storage space is sold in GB (1000000000 bytes) but measured in GiB (1024*1024*1024 bytes).

What they said. Don't forget "Memory for installable applications" - that's 2GB of that, plus your swap (~768KB) and some other fluff (IDK - haven't really looked) so that's ~3GB.

Edit: uh, that KB should be MB. Yup yup.

tap the drop down arrow at the top and tap memory details. everything is in there

Part of that flash memory is used by /home files system (2GB), and some part is used by system for swap (~800MB). Actually, MyDocs uses 28GB but not 27.

Is there a way to expand swap memory? To take from MyDocs and use it as swap? Like a virtual ram on pc.

You already have enough swap to make virtual memory 4 times the actual physical memory, it doesn't make much sense to have even more swap (which is now 3x physical memory). You risk serious slowdown at this point.

Swap memory is 'virtual ram' on a PC. With 256MB RAM and 768MB swap, you've got a full gigabyte of virtual memory, which is pretty much obscene for a phone.

Gotta take into account filesystem overhead as well. What is reported by almost any filesystem size program is going to be after the filesystem takes it's chunk of data. Thus the "something out of something" reporting is never going to be *exactly* what the device has.

Raw disk programs that calculates the blocks and such will show you an exact size, but yeah - just thought I'd mention that beside just GiB/GB there is also overhead. How much overhead is filesystem dependant, whether FAT/32, ext3, NTFS, ubifs, whatever...