Diskette Parameter Table
Diskette Parameter Table (DPT) is a group of bytes that stores the information about the active floppy disk that bootloader loaded from by BIOS.
It can be achieved using the Interrupt vector table in x86 microprocessor architecture family. The DPT's Interrupt index is 1Eh. The starting address of DPT can be achieved using LDS/LES REG16, [1Eh * 4] instructions in x86 microprocessors. The values in DPT are mostly used to calculate the Cylinder-head-sector address from linear addresses of data in the diskette.
Layout
A usual Diskette Parameter Table consists of 11 bytes:
| Offset | Description | |
|---|---|---|
| 00h | bits 7-4 : step rate bits 3-0 : head unload time | |
| 01h | bits 7-1 : head load time bit 0 : non-DMA mode (always 0) | |
| 02h | Delay until motor turned off. (In clock ticks) | |
| 03h | Bytes per sector. 00h = 128 01h = 256 02h = 512 03h = 1024 | |
| 04h | Sectors per track. (Maximum if different for different tracks.) | |
| 05h | length of gap between sectors 2Ah for 5.25" 1Bh for 3.5" | |
| 06h | Data length (Ignored if bytes-per-sector field nonzero) | |
| 07h | Gap length when formatting 50h for 5.25" 6Ch for 3.5" | |
| 08h | Format filler byte (default F6h) | |
| 09h | Head settle time in milliseconds | |
| 0Ah | Motor start time in 1/8 seconds | |
External links
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