这个都是过去DOS时代的汇编源码，虽然已经过去了，但是对于学习汇编还是有帮助的，汇编语言只是程序员一门基础语言，大多人掌握即可，不一定要深入研究.......
; DRIVESEX.ASM - Drive existence detection July 6th, 1994
; Code by : Lee Hamel (hamell@cs.pdx.edu)
; Partial credit: Paul Schlyter
;
; Goes through drives A-Z and determines if they:
; 1) Exist
; 2) Are removable or fixed
; 3) Are local, remote, or shared
; 4) Are a floppy, hard, RAM, subst, or CD-ROM drive
;
; Callable from C as: void Drives_Exist(void);
.model small
.286
DRIVEEXIST EQU 1
REMOVEDRV EQU 0
FIXEDDRV EQU 1
LOCALDRV EQU 0
REMOTEDRV EQU 1
SHAREDRV EQU 2
FLOPPY EQU 0
HARD EQU 1
RAM EQU 2
SUBST EQU 3
CDROM EQU 4
.data
PUBLIC _drives
_drives db 26 dup(0,1,0,1)
; default to not exist, fixed, local, hard drive
.code
PUBLIC _Drives_Exist
_Drives_Exist PROC NEAR
pusha
push es
mov ah,19h
int 21h ; get start drive
push ax ; save start drive
mov ax,40h
mov es,ax
mov bh,es:[10h] ; 40:10h is # of floppies-1
shr bh,6
inc bh ; # of actual floppy drives
mov bl,1
mov di,offset _drives
nextchkfloppy: mov ax,4409h ; check if drive exists
int 21h
jc nextsetfloppy
test dh,10000000b ; check if SUBST drive
jz chkfloppy
dec bh ; dec actual drive count
mov byte ptr [di+3],SUBST
setfloppyexist: mov byte ptr [di],DRIVEEXIST
jmp nextsetfloppy
chkfloppy: dec bh ; dec actual drive count
js nextsetfloppy
mov byte ptr [di+1],REMOVEDRV
mov byte ptr [di+3],FLOPPY
jmp setfloppyexist
nextsetfloppy: add di,4
inc bl
cmp bl,2 ; if B then jump back
je nextchkfloppy
mov ch,24 ; loop 24 times (drives C - Z)
mov cl,3 ; start at C:
drivechkloop: mov ax,4409h ; check if drive exists
mov bl,cl ; set drive letter
int 21h ; 0 = default, 1 = A:, etc.
jc nextsetdrv
mov byte ptr [di],DRIVEEXIST
mov ax,4408h ; check if removable
int 21h
mov byte ptr [di+1],al ; set REMOVABLE or FIXED
mov bx,dx
mov dl,dh
shr dl,7
and dh,00010000b
shr dh,4
mov byte ptr [di+2],dh ; set REMOTE or LOCAL
or dl,dl ; if not SUBST, then jump
jz chkremote
mov byte ptr [di+3],SUBST
jmp nextsetdrv
chkremote: cmp dh,REMOTEDRV ; if REMOTE, then check for CD ROM
je chkcdrom
test bh,00000010b ; sharable?
jz drivenoshare
mov byte ptr [di+2],SHAREDRV
drivenoshare: test bl,00000010b ; RAM drive?
jnz nextsetdrv
mov byte ptr [di+3],RAM
jmp nextsetdrv
chkcdrom: push cx
mov ax,1500h
xor bx,bx
int 2fh
pop cx
or bx,bx ; MSCDEX driver found?
jz nextsetdrv ; if not, jump to next drive setup
mov ax,150bh
dec cl ; 0=A:, etc.
int 2fh
inc cl
or ax,ax
jz nextsetdrv ; drive supported by MSCDEX?
mov byte ptr [di+3],CDROM
nextsetdrv: add di,4
inc cl
dec ch
jnz drivechkloop
pop dx
mov ah,0eh
int 21h ; reset start drive
pop es
popa
ret
_Drives_Exist ENDP
END