Пробую написать загрузчик для IO.SYS

SEGBIOS SEGMENT AT BIO_SEG
 
    ; Define the destination segment of the BIOS, including the
    ; initialization label
 
BIOS    LABEL   BYTE
 
SEGBIOS ENDS

BIO_SEG     EQU 70H     ; Destingation segment of BIOS
BIO_OFFSET  EQU 700H        ; Offset of bios

ORIGIN      EQU 7C00H       ; Origin of bootstrap LOADER

SEGBIOS SEGMENT AT BIO_SEG

jmp 70h:700h

jmp far ptr segbios: bios

DISKOK:
    mov CH,MediaByte
    mov DL,BootDrv
    mov BX,[BiosLow]        ; J.K.I1.Get bios sector in bx
    mov AX,[BiosHigh]       ; J.K.I1.
    jmp FAR PTR Bios        ;CRANK UP THE DOS

 mov     ch, ds:7C15h
seg000:0142                 mov     dl, ds:7C24h
seg000:0146                 mov     bx, ds:7C49h
seg000:014A                 mov     ax, ds:7C4Bh
seg000:014D                 jmp     far ptr 70h:0

end:                    ; We've got the file to load!
    pop ax              ; Clean up the stack (AX was pushed earlier)
    mov dl, byte [bootdev]      ; Provide kernel with boot device info
    mov ch, byte [MediumByte]
    mov bx, 21h         ;start of user data of disk 33 decimal
    mov ax, 0
 
    jmp 70h:0000h           ; Jump to entry point

        ; We now begin to load the BIOS in.
        ; All we have to do is just read is multiply the BioStartClus
        ; by SecsPerClust to find the logical sector for the start
        ; of the BIOS file. When this value is added to the double
        ; word BiosHigh:BiosLow we get the absolute sector offset
        ; for the start of the file and then read the  sectors
        ; contiguously IBM_LOAD_SIZE times. We here assume that
        ; IBMLOAD module is contiguous. Currently we estimate that
        ; IBMLOAD module will not be more than 3 sectors.
DoLoad:
    mov AX,[BX].DIR_FIRST   ; AX = BIOS starting cluster
    dec AX          ; Subtract first 2 reserved clusters
    dec AX
    mov BL,SecsPerClust     ; BX = Sectors per cluster
    xor BH,BH
    mul BX          ; DX:AX = first logical sector of bios
 
    add AX,[BiosLow]        ; Add absolute start sector
    adc DX,[BiosHigh]       ; DX:AX = Absolute bios sector offset
 
    mov BX,BIO_OFFSET       ;offset of ibmbio(IBMLOAD) to be loaded.
    mov CX,IBM_LOAD_SIZE    ;# of sectors to read.

jmp     far ptr 70h:0

ORIGIN      EQU 7C00H       ; Origin of bootstrap LOADER

    mov ax, 07C0h           ; Set data segment to where we're loaded
    mov ds, ax

push  70h
push  0
retf

xor ax,ax
mov es, ax
    
mov bx, 70h   ;адрес куда ложим IO.SYS
 
mov ah, 2           ; int 13h floppy read params
mov al, 1
 
push ax             ; Save in case we (or int calls) lose it
 
load_file_sector:
    mov ax, word [cluster]      ; Convert sector to logical
    add ax, 31
 
    call l2hts          ; Make appropriate params for int 13h
 
    xor ax, ax
    mov es, ax
    mov bx, word [pointer]
 
    pop ax              ; Save in case we (or int calls) lose it
    push ax
 
    stc
    int 13h
 
    jnc calculate_next_cluster  ; If there's no error...
 
 
 
;----------------------------------
 
 
end:                    ; We've got the file to load!
 
    pop ax              ; Clean up the stack (AX was pushed earlier)
 
    mov dl, byte [bootdev]      ; Provide kernel with boot device info
    mov ch, byte [MediumByte]
    mov bx, 21h         ;start of user data of disk 33 decimal
    mov ax, 0
 
    jmp 70h         ; Jump to entry point of loaded IO.SYS
 
;-----------------------------------------------
 
pointer     dw 70h  ; Pointer into Buffer, for loading IO.SYS

     1 00000000 EA00007000              jmp 112:0

     1 00000000 EA00007000              jmp 112:0
     2 00000005 E9(7000)                jmp 70h

BIO_SEG     EQU 70H     ; Destingation segment of BIOS
 
SEGBIOS SEGMENT AT BIO_SEG
 
    ; Define the destination segment of the BIOS, including the
    ; initialization label
 
BIOS    LABEL   BYTE
 
SEGBIOS ENDS

ASSUME  ES:CODE

mov ax, 07c0h
mov es, ax