Free space on hard drive

One of my computers, running Windows 98 SE, has a 4.3 GB SCSI HDD.

I regularly delete all the temporary internet files and all other temporary files.

However, whether I enter through “My Computer” or use chkdsk in DOS, the amount of free space can jump up or down by several hundred megabytes for no apparent reason.

Can you explain why this is, or if there is any way to get a consistent reading?

It is quite important to me because this is my workhorse computer on which all my files are stored, and I need to know just how much free space I have to play with.

I will add a second question. The computer (P 400) has 256 MB RAM. What would be the minimum hard drive space required for the swap file to function correctly?