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note about IBM welcoming other operating systems
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jpa
jpa
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While MS-DOS 2.0 added the MBR format, it actually didn't support using multiple partitions. Multiple partition support wasn't added until MS-DOS 3.3 in 1987.

Instead, the partition table was for dual-booting. From the PC-DOS 2.0 Manual:

If you intend to use part of the fixed disk with another operating system, then you should go to "Partitioning Your Fixed Disk" in this chapter.

The other operating system would typically be Xenix. From Xenix User's Handbook (1984):

Hard Disk Partitions

For this discussion, we assume that only two operating systems are to be resident on the hard disk. These two systems will be XENIX and MS-DOS.

In a sense the MBR was just crammed in to what would have been the boot sector on a floppy disk. Both floppy disks and hard drive MBR begin their first sector with executable code that the BIOS will load on boot. MBR just chooses to use the last 64 bytes of that sector to store information about partitions, and then pass control to the first sector of the partition.

IBM PC was surprisingly welcoming of alternate operating systems right from the start. The IBM PC/XT 5160 Guide to Operations even mentions in second paragraph of Section 3. Operating your IBM Personal Computer XT:

If you choose to write your own operating system, the IBM Personal Computer XT Technical Reference manual will provide valuable information.

While MS-DOS 2.0 added the MBR format, it actually didn't support using multiple partitions. Multiple partition support wasn't added until MS-DOS 3.3 in 1987.

Instead, the partition table was for dual-booting. From the PC-DOS 2.0 Manual:

If you intend to use part of the fixed disk with another operating system, then you should go to "Partitioning Your Fixed Disk" in this chapter.

The other operating system would typically be Xenix. From Xenix User's Handbook (1984):

Hard Disk Partitions

For this discussion, we assume that only two operating systems are to be resident on the hard disk. These two systems will be XENIX and MS-DOS.

In a sense the MBR was just crammed in to what would have been the boot sector on a floppy disk. Both floppy disks and hard drive MBR begin their first sector with executable code that the BIOS will load on boot. MBR just chooses to use the last 64 bytes of that sector to store information about partitions, and then pass control to the first sector of the partition.

While MS-DOS 2.0 added the MBR format, it actually didn't support using multiple partitions. Multiple partition support wasn't added until MS-DOS 3.3 in 1987.

Instead, the partition table was for dual-booting. From the PC-DOS 2.0 Manual:

If you intend to use part of the fixed disk with another operating system, then you should go to "Partitioning Your Fixed Disk" in this chapter.

The other operating system would typically be Xenix. From Xenix User's Handbook (1984):

Hard Disk Partitions

For this discussion, we assume that only two operating systems are to be resident on the hard disk. These two systems will be XENIX and MS-DOS.

In a sense the MBR was just crammed in to what would have been the boot sector on a floppy disk. Both floppy disks and hard drive MBR begin their first sector with executable code that the BIOS will load on boot. MBR just chooses to use the last 64 bytes of that sector to store information about partitions, and then pass control to the first sector of the partition.

IBM PC was surprisingly welcoming of alternate operating systems right from the start. The IBM PC/XT 5160 Guide to Operations even mentions in second paragraph of Section 3. Operating your IBM Personal Computer XT:

If you choose to write your own operating system, the IBM Personal Computer XT Technical Reference manual will provide valuable information.

Source Link
jpa
jpa
  • 978
  • 7
  • 11

While MS-DOS 2.0 added the MBR format, it actually didn't support using multiple partitions. Multiple partition support wasn't added until MS-DOS 3.3 in 1987.

Instead, the partition table was for dual-booting. From the PC-DOS 2.0 Manual:

If you intend to use part of the fixed disk with another operating system, then you should go to "Partitioning Your Fixed Disk" in this chapter.

The other operating system would typically be Xenix. From Xenix User's Handbook (1984):

Hard Disk Partitions

For this discussion, we assume that only two operating systems are to be resident on the hard disk. These two systems will be XENIX and MS-DOS.

In a sense the MBR was just crammed in to what would have been the boot sector on a floppy disk. Both floppy disks and hard drive MBR begin their first sector with executable code that the BIOS will load on boot. MBR just chooses to use the last 64 bytes of that sector to store information about partitions, and then pass control to the first sector of the partition.