The original IBM PCs and XTs were made before High Density FDD's caught on, and as a result of this, no intentional support were added in neither hardware or software. In order to get HD drives to work on a PC or XT, we have to work around therse limitations.
[h="1"]Hardware[/h]
The original IBM Floppy disk controller was based around a simple microcontroller for controll and a bunch of custom logic for interfacing. This card was intended to be used with Double-Density drives, and it's unable to interface with HD drives due to timing issues (unless the HD drive emulates a DD drive when DD media is present). In order for the computer to properly interface with HD drives, the controller must be replaced with a more recent one with support for HD drives.
Controllers as found on AT-style multifunction cards works well, as they mostly only use the 8-bit partion of the card's 16-bit bus. With a HD-compatible controller, the computer will at least be able to interface with HD drives.
[h="1"]Software[/h]
The next limitation is the BIOS. By default, the BIOS can't really make too much sense of more recent formats, even though it may be able to read and write correctly to DD disks of any size. HD disks may still be unreadable, and will in that case just generate errors when access is attempted. In order to solve this problem, a more recent replacement of the BIOS diskette routine package (Int 13h) must be installed.
Some HD controllers come with a replacement in a physical ROM chip on the card itself. This replacement is automatically loaded on boot, and all you have to make sure is that the switches on the card are set correctly.
If this is not the case, a replacement will have to be installed by a software driver after the machine boots, usually as a part of the OS initialization. An example of such a driver is '2M-XBIOS.COM' from the 2M FD-tool package[footnote]http://en.wikipedia.org/wiki/2M_(DOS)[/footnote]. If the machine has an HDD, this will be no problem since the driver is not needed for the HDD to boot properly, but if the machine only has floppy drives, a startup disk of Double-Density has to be used in order to install the driver. This disk must of course be formated as a startup disk, and it must also contain the driver. You should make sure to read how to set up the driver before installing it (this information usually provided with the driver).
[wiki]Category:How_To[/wiki]
[h="1"]Hardware[/h]
The original IBM Floppy disk controller was based around a simple microcontroller for controll and a bunch of custom logic for interfacing. This card was intended to be used with Double-Density drives, and it's unable to interface with HD drives due to timing issues (unless the HD drive emulates a DD drive when DD media is present). In order for the computer to properly interface with HD drives, the controller must be replaced with a more recent one with support for HD drives.
Controllers as found on AT-style multifunction cards works well, as they mostly only use the 8-bit partion of the card's 16-bit bus. With a HD-compatible controller, the computer will at least be able to interface with HD drives.
[h="1"]Software[/h]
The next limitation is the BIOS. By default, the BIOS can't really make too much sense of more recent formats, even though it may be able to read and write correctly to DD disks of any size. HD disks may still be unreadable, and will in that case just generate errors when access is attempted. In order to solve this problem, a more recent replacement of the BIOS diskette routine package (Int 13h) must be installed.
Some HD controllers come with a replacement in a physical ROM chip on the card itself. This replacement is automatically loaded on boot, and all you have to make sure is that the switches on the card are set correctly.
If this is not the case, a replacement will have to be installed by a software driver after the machine boots, usually as a part of the OS initialization. An example of such a driver is '2M-XBIOS.COM' from the 2M FD-tool package[footnote]http://en.wikipedia.org/wiki/2M_(DOS)[/footnote]. If the machine has an HDD, this will be no problem since the driver is not needed for the HDD to boot properly, but if the machine only has floppy drives, a startup disk of Double-Density has to be used in order to install the driver. This disk must of course be formated as a startup disk, and it must also contain the driver. You should make sure to read how to set up the driver before installing it (this information usually provided with the driver).
[wiki]Category:How_To[/wiki]