IBM 5170 Technical Reference page 150

Interrupt ID--Video Parameters:
This vector points to a data
region containing the parameters required for the initialization of
the 6845 on the video adapter. Notice that there are four
separate tables, and all four must be reproduced if all modes of
operation are to be supported. The power-on routines initialize
this vector to point to the parameters contained in the ROM video
routines.
Interrupt lE--Diskette Parameters:
This vector points to a
data region containing the parameters required for the diskette
drive. The power-on routines initialize this vector to point to the
parameters contained in the ROM diskette routine. These default
parameters represent the specified values for any mM drives
attached to the system. Changing this parameter block may be
necessary to reflect the specifications of other drives attached.
Interrupt 1 F --Graphics Character Extensions:
When
operating in graphics modes 320 x 200 or 640 x 200, the
read/write character interface will form a character from the
ASCII code point, using a set of dot patterns. ROM contains the
dot patterns for the first 128 code points. For access to the
second 128 code points, this vector must be established to point
at a table of up to lKb, where each code point is represented by 8
~
bytes of graphic information. At power-on time, this vector is
initialized to 000:0, and the user must change this vector if the
additional code points are required.
Interrupt 40--Reserved:
When an mM Personal Computer AT
Fixed Disk and Diskette Drive Adapter is installed, the BIOS
routines use interrupt 40 to revector the diskette pointer.
Interrupt 41 and 46:
These vectors point to the parameters for
the fixed disk drives, 41 for the first drive and 46 for the second.
The power on routines initialize the vectors to point to the
appropriate parameters in the ROM disk routine if CMOS is
valid. The drive type codes in CMOS are used to select which
parameter set the vector points to. Changing this parameter hook
may be necessary to reflect the specifications of other fixed drives
attached.
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5-8
System BIOS