Maximum Hard Drive Space Under LAN Manager (94124)

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On a LAN Manager 2.1 server, three possible file systems may be running: FAT, HPFS, and HPFS386. The FAT and HPFS file systems are 16-bit based, whereas the HPFS386 takes advantage of the 32-bit capabilities of the 80386/486 processors.

Under all three systems, the largest any physical drive can be is 7.8 gigabytes (GB) because of the current limits of disk geometry. Drives are referenced by cylinders, heads, sectors, and bytes per sector. Currently, cylinders are limited to 1024, heads to 256, sectors to 63, and bytes per sector to 512. Thus, the 7.8 GB limit when using the following equation:

   cylinders * heads * sectors * bytes/sector = drive size in bytes
				

If any drive has physical parameters larger than these, these parameters are translated by adding one to offset the other; for example, the apparent number of heads may be increased, thereby decreasing the number of cylinders. This is handled by disk drivers, drive controller ROMs, or a combination of the two, so that the file system thinks the drive is within limits.

Under the FAT (file allocation table) and HPFS (high performance File system), the largest any one partition (a logical division of a hard drive) can be is 2 GB. Under HPFS386, with its 32-bit addressability, a partition can be as large as 7.8 GB, or the limit of the physical drive. HPFS386 could support partitions as large as 64 GB if it were possible to map that amount of space to a physical drive (which is not currently possible because of the limits discussed above).

With this knowledge and the fact that there are only 24 possible logical hard drives (26 letters in the English alphabet, minus 2 for floppy disk drives A and B, allowed in most systems) there is an upper limit of 48 GB under FAT and HPFS, and 187 GB under HPFS386.

Any individual file is limited to 2 GB.