Tandy 1000 HX Technical Reference Manual page 410

Entry Conditions:
AH = 2
DL = drive number (0-1)
DH = head number (0-1)
CH = track number (0-79)
CL = sector number (1 to 9)
AL = sector count (1 to 9)
ES:BX = pointer to disk buffer
Exit Conditions:
See "Exits From All Calls" below.
AL = number of sectors read
Write Sector(s) to Floppy Disk
Write the desired sector(s) from RAM to disk.
Entry Conditions:
AH = 3
DL = drive number (0-1)
DH = head number (0-1)
CH = track number (0-79)
CL = sector number (1 to 9)
AL = sector count (1 to 9)
ES:BX = pointer to disk buffer
Exit Conditions:
See "Exits From All Calls" below.
AL = number of sectors written
Verify Sector(s) on Floppy Disk
Verify the desired sector(s).
Entry Conditions:
AH = 4
DL = drive number (0-1)
DH = head number (0-1)
CH = track number (0-79)
CL = sector number (1 to 9)
AL = sector count (1 to 9)
Exit Conditions:
See "Exits From All Calls" below.
AL = number of sectors verified
20