Web Presentation and Text Copyright©2006 by Daniel B. Sedory
NOT to be reproduced in any form without Permission of the Author !
The IVT (Interrupt Vector Table) generally contains far pointers
to each of the PC's 256 Interrupts (each Segment:Offset pair; for a total of
4 bytes x 256 pointers = 1,024 bytes, or two 512-byte sectors).
This table is located at the very beginning of the PC's Memory! (That is: locations 0000:0000 through 0000:03FF) However, the PC commonly uses less than half that space (under 512 bytes) for actual vectors.
Interrupt Vector Table,
Interrupt Descriptor Table.
Interrupt 1E Vector to Diskette Controller Parameters (located at: 0000:0078) DWORD Address points to data table that is used by BIOS. Default location is at 0F000:0EFC7 with an 11-byte Table format: 00h 4-bit Step Rate, 4-bit Head Unload Time 01h 7-bit Head Load Time, 1-bit DMA Flag 02h 54.9254 ms counts - delay till motor off (37-38 typical) 03h Sector Size: 00h = 128 bytes 01h = 256 bytes 02h = 512 bytes 03h = 1024 bytes 04h Last Sector on track (8 or 9 typical) 05h Gap between sectors on read/write (42 typical) 06h Data Length for DMA transfers (0FFh typical) 07h Gap Length between sectors for FORMAT (80 typical) 08h Sector Fill Byte for FORMAT command (0F6h typical) 09h Head Settle Time (in milliseconds) (15 to 25 typical) DOS 1.0 0 DOS 2.10 15 DOS 3.1 1 10h Motor Start Time (in 1/8 second intervals) (2 to 4 typical) DOS 2.10 2 Notes: 1) This vector is pointed to the ROM BIOS diskette table on system initialization. 2) IBM recommends that this table needs to be modified, that it should be copied into RAM and only the required changes be made.
Updates: July 31, 2006 (2006.07.31).
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