IBM 5150 Technical Reference page 100

Interrupt Hex IE - Diskette Parameters
This vector points to a data region containing the parameters
required for the diskette drive. The power-on routines initialize
the vector to point to the parameters contained in the ROM
diskette routine. These default parameters represent the specified
values for any IBM drives attached to the system. Changing this
parameter block may be necessary to reflect the specifications of
the other drives attached.
Interrupt Hex IF - Graphics Character Extensions
When operating in the graphics modes of the IBM
Color/Graphics Monitor Adapter (320 by 200 or 640 by 200),
the read/write character interface forms the character from the
ASCII code point, using a set of dot patterns. The dot patterns
for the first 128 code points are contained in ROM. To access
the second 128 code points, this vector must be established to
point at a table of up to 1K bytes, where each code point is
represented by eight bytes of graphic information. At power-on,
this vector is initialized to 000:0, and it is the responsibility of the
user to change this vector if additional code points are required.
Interrupt Hex 40 - Reserved
When an IBM Fixed Disk Adapter is installed, the BIOS routines
use interrupt hex 30 to revector the diskette pointer.
Interrupt Hex 41 - Fixed Disk Parameters
This vector points to a data region containing the parameters
required for the fixed disk drive. The power-on routines initialize
the vector to point to the parameters contained in the ROM disk
routine. These default parameters represent the specified values
for any IBM fixed disk drives attached to the system. Changing
~
this parameter block may be necessary to reflect the specifications
of the other fixed disk drives attached.
System BIOS 5-7