Bit(s) Description (Table 00226)
0 floppy disk(s) installed (number specified by bits 7-6)
1 80x87 coprocessor installed
3-2 number of 16K banks of RAM on motherboard (PC only).
Number of 64K banks of RAM on motherboard (XT only)
2 pointing device installed (PS)
3 unused (PS)
5-4 initial video mode.
00 EGA, VGA, or PGA.
01 40x25 color.
10 80x25 color.
11 80x25 monochrome
7-6 number of floppies installed less 1 (if bit 0 set)
8 DMA support installed (PCjr, Tandy 1400LT).
DMA support *not* installed (Tandy 1000's)
11-9 number of serial ports installed
12 game port installed
13 serial printer attached (PCjr).
Internal modem installed (PC/Convertible)
15-14 number of parallel ports installed
---Compaq, Dell, and many other 386/486 machines--
23 page tables set so that Weitek coprocessor addressable in real mode
24 Weitek math coprocessor present
---Compaq Systempro---
25 internal DMA parallel port available
26 IRQ for internal DMA parallel port (if bit 25 set).
0 = IRQ5.
1 = IRQ7
28-27 parallel port DMA channel.
00 DMA channel 0.
01 DMA channel 0 ???.
10 reserved.
11 DMA channel 3

Notes: Some implementations of Remote (Initial) Program Loader (RPL/RIPL) don't set bit 0 to indicate a "virtual" floppy drive, although the RPL requires access to its memory image through a faked drive A:. This may have caused problems with releases of DOS 3.3x and earlier,

which assumed A:And B: to be invalid drives then and would discard
any attempts to access these drives. Implementations of RPL should
set bit 0 to indicate a "virtual" floppy..
The IBM PC DOS 3.3x-2000 IBMBIO.COM contains two occurences of code
sequences like:
INT 11h
JMP SHORT skip
DB 52h,50h,53h; "RPS"
skip:OR AX,1
TEST AX,1
While at the first glance this seems to be a bug since it just
wastes memory and the condition is always true, this could well be
a signature for an applyable patch to stop it from forcing AX bit 0
to be always on. MS-DOS IO.SYS does not contain these signatures,
however.

BUGs: Some old BIOSes didn't properly report the count of floppy drives installed to the system. In newer systems INT 13h/AH=15h can be used to retrieve the number of floppy drives installed.. Award BIOS v4.50G and v4.51PG erroneously set bit 0 even if there are no floppy drives installed; use two calls to INT 13/AH=15h to determine whether any floppies are actually installed