The maximum size for a disk volume under OS/2 Version 2.0 is 512GB using HPFS and 2GB using the FAT file system, with the following conditions:
When a machine's BIOS reports on the characteristics of a disk, it returns three values; it determines the number of sectors per head, the number of heads per cylinder, and the number of cylinders. The IBM BIOS sets the disk geometry such that one cylinder equals one megabyte of disk storage. For IBM disk drives, 1023 cylinders corresponds to one gigabyte. Other manufacturers may use different sector and head values causing the 1023 cylinder limit to be greater than or less than one gigabyte.
It may also not exceed 2GB even if, due to the manufacturer's disk geometry,
the 1023rd cylinder is beyond 2GB.
Imagine a 10GB disk where the geometry of the disk has sector/head/cylinder values such that the 1023rd cylinder corresponds to 7.4GB, as is the case with some OEM SCSI disks. Using the FAT file system, the way to configure the volumes to maximize their size would be to have three volumes of 2GB and one volume of 1.4GB. In this case the 2.6GB of free space (beyond the 1023rd cylinder) would be unusable by OS/2 using the FAT file system. These volumes may exist in primary partitions or an extended partition, or both. In an extended partition, the volume would occupy one or more of the logical partitions defined in the extended partition.
Although an HPFS volume can take up the entire disk, for performance reasons the practical limit is much less than 512GB.
There are 24 drive letters available for hard disk drives (a: and b: are reserved for diskette drives), and currently the largest tested IBM SCSI hard disk available for the PS/2 is 400MB. Using 24 single SCSI disks chained on four SCSI adapters we would get a maximum of 24 x 400MB, or 9.6GB of online DASD.