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Most systems support up to four SCSI host adapters, each with up to seven hard disk drives, for a total 28 physically installed drives.

ROM BIOS Capacity Limitations

In addition to the capacity limit of 504MB, the standard ROM BIOS is limited to supporting only two hard disk drives. The enhanced BIOS is limited to 128 drives maximum. Most SCSI and IDE adapters get around the two-drive standard BIOS limits by incorporating an enhanced BIOS on board that takes over the disk interface. Some of the newer adapter on-board BIOS versions support booting from CD-ROM drives as well.

Operating System Capacity Limitations

IBM and Microsoft officially say that DOS 5 and later versions will support up to eight physical hard disks. IBM says that OS/2 1.30.1 and later versions (including 2.x) support up to 24 physical hard disks, and because OS/2 includes DOS, that implies that DOS under OS/2 would support 24 physical drives as well. OS/2 HPFS (High Performance File System) also supports a maximum partition size of 8GB and a maximum single-file size of 2GB, whereas DOS and OS/2 FAT partitions have a maximum size of 2GB and a maximum single-file size of 2GB. FAT32 in Windows 95 OSR2 and Windows 98 allows a single volume of 2T or 2048GB. As you have seen, BIOS limitations currently limit the maximum physical hard disk size to about 7.88GB (or about 8.46 million bytes).

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