IBM Options and Adapters - IBM Fixed Disk Adapter
The IBM Fixed Disk Adapter section of IBM's Options and Adapters technical reference is the manufacturer's own reference for the MFM hard-disk controller shipped in the IBM PC XT.
What it contains
[edit | edit source]- Description — attachment of one or two drives through an internal daisy-chained data/control cable, a maximum of one adapter and two drives per system, buffering on the I/O bus, use of the system board's DMA and of an interrupt level, and automatic 11-bit burst error detection and correction by way of 32-bit ECC. IBM also warns that the last cylinder is reserved for diagnostics and that the diagnostic write test destroys any data on it.
- Programming — the status register, the sense bytes, the data register, the control byte and the full command summary.
- Interface — the I/O address range hex 320 to hex 323, the controller-select pulse written to hex 322, and the adapter ROM decoded between hex C8000 and hex C9FFF.
- BIOS listing — the complete commented assembler source of the adapter's own device-level control ROM, including the power-on diagnostic that displays 1701 when it fails.
- Logic diagrams — the full schematic.
Download it here: IBM Options and Adapters - IBM Fixed Disk Adapter.pdf