Windows 95, when released, provided the world with a GUI (Graphical User Interface) that did not require MS-DOS as a foundation for functionality. The first version of Windows 95 (95A) carried with it all of the FAT 16-based limitations that it's predecessor (MS-DOS) had. The Windows 95 Upgrade release was also limited to the actual drive capacities that it could support as well.
Windows 95 B (OSR2) is a newer, enhanced Operating System released by Microsoft. One of the key components to this revision is the FAT 32 file system. FAT 32 has the capability of supporting hard drives with capacities up to 32 Terabytes (TB) (e.g., FAT 32 will create a cluster size of 4 KB on partitions smaller than 8 GB). It is also crucial to point out that Windows 95 B was not openly available to the retail consumer. The reason for this was that it had no upgrade track; it had to be loaded from scratch as a complete operating system. Windows 95 B could only be found on computers shipped from OEMs (Original Equipment Manufacturers). Microsoft also briefly released revision 95C. This revision possessed all of the characterisitics of 95B, but was enhanced due to the new capabilities and additions of the Internet Explorer Web Browser.