Descrepency in HDD Space

I just added a WD 40 GB HDD to my PC, and ghosted the contents of the system’s original 8GB HDD. I’ve set up the 40 as the master, and the 8 as the slave. When I boot into Win98 SE and check the HDD space of both devices, the 8 shows that 5.54 is is use, and the 40 has 6.41 in use. The system has 192 MB RAM. I have added nothing to the new HDD. I thought that it may be the swap file, but the swap file is less than 150 MB. Why else might there be a difference, is it the cluster size? Thanks!