Int 41

SYSTEM DATA - HARD DISK 0 PARAMETER TABLE ADDRESS [NOT A VECTOR!]

Notes: The default parameter table array is located at F000h:E401h in 100% compatible BIOSes; the pointer may be overridden by the hard disk controller's BIOS to support drive formats unknown to the ROM BIOS. Not used by some PS/2 models. BIOSes which support four hard drives may store the parameter tables for drives 81h-83h immediately following the parameter table pointed at by INT 41, with a separate copy of the drive 81h table for INT 46. The check for such an arrangement is to test whether INT 46 points somewhere other than exactly 16 bytes past INT 41, and the sixteen bytes starting at offset 10h from INT 41 are identical to the sixteen bytes pointed at by INT 46. Another arrangement for BIOSes which support four IDE drives is to have four tables pointed at by INT 41 in the order primary master, primary slave, secondary master, and secondary slave, in which case (for example) a system with only primary master and secondary master will have valid tables at offsets 00h and 20h, with garbage (but sectors-per-track = 00h) at offsets 10h and 30h

Format of fixed disk parameters: Offset Size Description (Table 03196) 00h WORD number of cylinders 02h BYTE number of heads 03h WORD starting reduced write current cylinder (XT only, 0 for others) 05h WORD starting write precompensation cylinder number 07h BYTE maximum ECC burst length (XT only) 08h BYTE control byte (see #03197,#03198) 09h BYTE standard timeout (XT only, 0 for others) 0Ah BYTE formatting timeout (XT and WD1002 only, 0 for others) 0Bh BYTE timeout for checking drive (XT and WD1002 only, 0 for others) 0Ch WORD cylinder number of landing zone (AT and later only) 0Eh BYTE number of sectors per track (AT and later only) 0Fh BYTE reserved

See Also: #00273 - #00277


Bitfields for XT fixed disk control byte:

Bit(s)  Description     (Table 03197)
2-0    drive step speed.
000  3ms.
100  200ms.
101  70ms (default).
110  3ms.
111  3ms
5-3    unused
6      disable ECC retries
7      disable access retries

Bitfields for AT fixed disk control byte:

Bit(s)  Description     (Table 03198)
0      unused
1      reserved (0)  (disable IRQ)
2      reserved (0)  (no reset)
3      set if more than 8 heads
4      always 0
5      set if manufacturer's defect map on max cylinder+1  (AT and later only)
6      disable ECC retries
7      disable access retries

Category: Bios - Int 41h - S

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