; **************************************************************************** ; R5HDBOOT.ASM (R5HDBOOT.COM) - Retro DOS v5 Hard Disk Boot Sector Utility ; (for MSDOS/WINDOWS) ; ---------------------------------------------------------------------------- ; Last Update: 29/01/2026 ; ---------------------------------------------------------------------------- ; Beginning: 03/05/2024 ; ---------------------------------------------------------------------------- ; Assembler: NASM version 2.15 (r5hdboot.s) ; ---------------------------------------------------------------------------- ; Modified from 'trhdboot.s'(TRHDBOOT.COM) source code by Erdogan Tan ; (12/09/2020) - TRDOS 386 v2 hard disk boot sector modification utility - ; **************************************************************************** ; assembling: nasm r5hdboot.s -l r5hdboot.txt -o R5HDBOOT.COM -Z error.txt ; ---------------------------------------------------------------------------- ; equations ; ---------------------------------------------------------------------------- ; boot sector parameters bsOemName equ 3 ; ('MSWIN4.1') --> 'RETRODOS' ; 03/05/2024 bsBytesPerSec equ 11 ; 512 (word) bsSecPerClust equ 13 bsResSectors equ 14 bsFATs equ 16 bsRootDirEnts equ 17 bsSectors equ 19 bsMedia equ 21 ; 0F8h bsFATsecs equ 22 bsSecPerTrack equ 24 bsHeads equ 26 bsHidden1 equ 28 bsHidden2 equ 30 bsHugeSectors equ 32 ; FAT 16 bs & FAT 12 bs bsDriveNumber equ 36 ; 80h bsReserved1 equ 37 bsBpbSignature equ 38 ; 29h (byte) bsVolumeID equ 39 bsVolumeLabel equ 43 bsFileSysType equ 54 ; 'FAT16 ' (8 bytes) ; FAT 32 bs BPB_FATSz32 equ 36 BPB_ExtFlags equ 40 BPB_FSVer equ 42 BPB_RootClus equ 44 BPB_FSInfo equ 48 BPB_BkBootSec equ 50 BPB_Reserved equ 52 BS_DrvNum equ 64 ; 80h BS_Reserved1 equ 65 BS_BootSig equ 66 ; 29h (byte) BS_VolID equ 67 BS_VolLab equ 71 BS_FilSysType equ 82 ; 'FAT32 ' (8 bytes) ; Masterboot / Partition Table at Beginning+1BEh ptBootable equ 0 ptBeginHead equ 1 ptBeginSector equ 2 ptBeginCylinder equ 3 ptFileSystemID equ 4 ptEndHead equ 5 ptEndSector equ 6 ptEndCylinder equ 7 ptStartSector equ 8 ptSectors equ 12 partition_table equ 1BEh ; ---------------------------------------------------------------------------- ; code ; ---------------------------------------------------------------------------- [BITS 16] [ORG 100h] cli cld push cs pop ss mov sp, 0FFFEh sti ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; see if drive specified ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - mov si, 80h ; PSP command tail mov cl, [si] or cl, cl jz short T_9 ; jump if zero T_1: inc si mov al, [si] cmp al, ' ' ; is it SPACE ? jne short T_2 dec cl jnz short T_1 jmp short T_9 T_2: inc si cmp byte [si], ':' je short T_3 cmp byte [si], ' ' jna short T_3 cmp al, 'h' jne short T_9 cmp byte [si], 'd' jne short T_9 inc si mov al, [si] cmp al, '0' je short T_8 jb short T_9 cmp al, '3' jna short T_8 jmp short T_9 T_3: cmp al, 'C' jb short T_9 je short T_6 ;cmp al, 'Z' ; A - Z ;jna short T_6 cmp al, 'D' jna short T_6 cmp al, 'Z' jna short T_9 T_4: cmp al, 'c' ; a - z jb short T_9 je short T_5 ;cmp al, 'z' ;ja short T_9 cmp al, 'd' ja short T_9 T_5: sub al, 'a'-'A' ; to upper case ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; get drive code ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - T_6: sub al, 'C'-'0' T_7: mov [RD5_Drive], al ; '0' .. '4' jmp short T_10 T_8: inc si cmp byte [si], ' ' jna short T_7 ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; Write message ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - T_9: mov si, RD5_Welcome call print_msg ;cmp cl, 0 ;ja short T_35 jmp T_35 ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; get drive parameters ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - T_10: mov ah, 08h ;mov dl, [RD5_Drive] ; drive mov dl, al add dl, 80h -'0' ; make it 80h based mov [drv], dl int 13h ; return disk parameters push cs pop es ; restore es or ah, ah jnz short T_12 ; error mov al, cl and al, 63 mov [sectors], al shr cl, 6 xchg ch, cl inc cx mov [cylinders], cx inc dh mov [heads], dh mul dh ; ax = heads * spt mul cx ; * cylinders ; dx:ax = chs limit mov [CHS_limit], ax mov [CHS_limit+2], dx ; check for (valid) primary dos partition ;mov byte [RetryCount], 4 ;mov ax, 0201h ; read disk mov bx, MBR ; location of masterboot code mov cx, 1 ; cylinder = 0 ; sector = 1 mov dh, 0 ; head = 0 ;mov dl, [RD5_Drive] ; drive ;add dl, 80h -'0' ; make it 80h based mov dl, [drv] T_11: mov ax, 0201h int 13h ;jc short T_12 jnc short T_13 ; read masterboot sector, OK dec byte [RetryCount] jnz short T_11 T_12: mov byte [zbyte], 0 call T_37 ; write error message jmp T_35 ; terminate T_13: cmp word [MBR+510], 0AA55h jne short T_12 mov si, MBR+(partition_table+ptFileSystemID) T_14: call validate_primary_dos_partition jnc short T_15 add si, 16 cmp si, MBR+partition_table+ptFileSystemID+64 jb short T_14 mov si, RD5_fatp_notfound call print_msg jmp T_35 T_15: ; valid primary dos partition ; al = FAT type (1,2,3) ; ah = partition type mov byte [fattype], al cmp al, 2 je short T_17 ; FAT16 BS (default offset addr) jb short T_16 ; set Retro DOS v5 BS pointer for FAT32 BS mov word [retrodosv5bs], RD5_FAT32_hd_bs ; set FS type string mov word [fattype_str],'32' ; 'FAT32' ; ok.. read boot sector jmp short T_17 T_16: ; set Retro DOS v5 BS pointer for FAT12 BS mov word [retrodosv5bs], RD5_FAT12_hd_bs mov byte [fattype_str+1],'2' ; 'FAT12' T_17: mov byte [RetryCount], 5 add si, ptStartSector-ptFileSystemID mov ax, [si] mov dx, [si+2] mov [dosp_start], ax mov [dosp_start+2], dx add si, ptSectors-ptStartSector mov cx, [si] mov bx, [si+2] mov [dosp_size], cx mov [dosp_size+2], bx add cx, ax adc bx, dx jc short T_12 cmp bx, [CHS_limit+2] mov bx, bootsector ja short T_20 ; LBA read/write jb short T_18 cmp cx, [CHS_limit] ja short T_20 T_18: ; CHS read sub si, ptSectors-ptBeginHead mov dh, [si] ; head inc si mov cx, [si] ; sector ; cl = sector, ch = cylinder ;mov bx, bootsector mov dl, [drv] mov [_dh], dh mov [_cx], cx T_19: mov ax, 0201h ; read one sector int 13h jnc short T_22 ; OK dec byte [RetryCount] jnz short T_19 jmp T_12 T_20: ; LBA read mov byte [lba], 1 ;mov ax, [dosp_start] ;mov dx, [dosp_start+2] T_21: ;pusha ; db 60h db 60h ;push 0 ; db 6Ah, 00h db 6Ah, 0 ;push 0 ; db 6Ah, 00h db 6Ah, 0 push dx push ax push es push bx ;push 1 ; db 6Ah, 01h db 6Ah, 01h ;push 10h ; db 6Ah, 10h db 6Ah, 10h mov dl, [drv] mov ah, 42h mov si, sp int 13h ;popa db 61h ;popa db 61h jnc short T_22 dec byte [RetryCount] jz T_12 mov ax, [dosp_start] mov dx, [dosp_start+2] jmp short T_21 T_22: cmp word [bootsector+510], 0AA55h jne short T_23 cmp word [bootsector+bsBytesPerSec], 512 jne short T_23 cmp byte [bootsector+bsMedia], 0F8h jne short T_23 cmp byte [fattype], 2 ja short T_24 cmp byte [bootsector+bsBpbSignature], 29h jne short T_23 cmp dword [bootsector+bsFileSysType], 'FAT1' jne short T_23 mov cx, 54-11 ; byte count to be copied mov al, [bootsector+bsFileSysType+4] cmp al, '6' je short T_25 cmp al, '2' je short T_25 T_23: mov si, RD5_invalid_bootsector call print_msg jmp T_35 T_24: ; 03/05/2024 cmp word [bootsector+bsFATsecs], 0 ja short T_23 ; not FAT32 fs cmp byte [bootsector+BS_BootSig], 29h jne short T_23 cmp dword [bootsector+BS_FilSysType], 'FAT3' jne short T_23 cmp byte [bootsector+BS_FilSysType+4], '2' jne short T_23 mov cx, 82-11 ; byte count to be copied T_25: mov si, RD5_Do_you_want call print_msg T_26: ;xor ax, ax ;int 16h ; wait for keyboard command ;cmp al, 'y' ;je short T_27 ; retry ;cmp al, 'Y' ;je short T_27 ;cmp al, 'n' ;je short T_35 ; exit ;cmp al, 'N' ;je short T_35 ;cmp al, 'C'-40h ;je short T_35 ;cmp al, 27 ;je short T_35 ;jmp short T_26 call get_answer cmp al, 'Y' je short T_27 mov si, _no_str call print_msg jmp T_35 T_27: mov si, _yes_str call print_msg ;mov si, RD5_CRLF ;call print_msg ; set 'RETRODOS' as OEM name mov di, [retrodosv5bs] add di, bsOemName mov ax, 'RE' stosw mov ax, 'TR' stosw mov ax, 'OD' stosw mov ax, 'OS' stosw ; DI points to retrodosv5bs+bsBytesPerSec mov si, bootsector+bsBytesPerSec rep movsb mov si, RD5_PressKeyWhenReady call print_msg T_28: xor ax, ax int 16h ; wait for keyboard command cmp al, 'M'-40h ; Enter (OK) key je short T_29 ; write cmp al, 'C'-40h je short T_35 ; no write (exit) cmp al, 27 je short T_35 jmp short T_28 T_29: mov si, RD5_CRLF call print_msg T_30: ;xor ax, ax ;int 1Ah ; get time of day ;mov si, volume_id ;mov [si], dx ;mov [si+2], cx ; set unique volume ID ;mov ah, 02h ; Return Current Time ;int 1Ah ;xchg ch, cl ;xchg dh, dl ;add cx, dx ;add [si+2], cx ;mov ah, 04h ; Return Current Date ;int 1Ah ;xchg ch, cl ;xchg dh, dl ;add cx, dx ;add [si+2], cx ;mov ax, [vol_id] ;mov dx, [vol_id+2] mov bx, [retrodosv5bs] ; location of boot code ; es: bx = boot sector buffer address ;mov si, bx ;add si, bsVolumeID ;cmp byte [fattype], 3 ;jne short T_31 ;add si, BS_VolID-bsVolumeID ;T_31: ;mov [si], ax ;mov [si+2], dx cmp byte [lba], 1 jnb short T_32 ; LBA write mov dl, [drv] ; drive mov dh, [_dh] ; head mov cx, [_cx] ; cl = sector, ch = cylinder (low 8 bits) T_31: mov ax, 0301h ; write to disk ; es: bx = boot sector buffer address int 13h jnc short T_34 ; ok ; error dec byte [RetryCount] jnz short T_31 call T_37 jmp short T_36 T_32: mov ax, [dosp_start] mov dx, [dosp_start+2] T_33: ;pusha ; db 60h db 60h ;push 0 ; db 6Ah, 00h db 6Ah, 0 ;push 0 ; db 6Ah, 00h db 6Ah, 0 push dx push ax push es push bx ;push 1 ; db 6Ah, 01h db 6Ah, 01h ;push 10h ; db 6Ah, 10h db 6Ah, 10h mov dl, [drv] mov ah, 43h ; LBA write xor al, al ; verify off mov si, sp int 13h ;popa db 61h ;popa db 61h jnc short T_34 dec byte [RetryCount] jnz short T_32 call T_37 jmp short T_36 ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; success. try again ? ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - T_34: cmp byte [fattype], 3 ; FAT32 je short T_40 mov si, RD5_disk_WrittenSuccesfully call print_msg T_35: mov si, RD5_CRLF call print_msg mov ax, 4C00h ; terminate int 21h T_36: ;xor ax, ax ;int 16h ; wait for keyboard command ;cmp al, 'y' ;je short TX_15 ; retry ;cmp al, 'Y' ;je short TX_15 ;cmp al, 'n' ;je short T_35 ; exit ;cmp al, 'N' ;je short T_35 ;cmp al, 'C'-40h ;je short T_35 ;cmp al, 27 ;je short T_35 ;jmp short T_36 call get_answer cmp al, 'Y' je short T_29 jmp short T_35 T_37: mov si, RD5_disk_NotReadyOrError ;;call print_msg ;;jmp short T_36 ;jmp short print_msg print_msg: T_38: lodsb ; Load byte at DS:SI to AL and al, al jz short T_39 mov ah, 0Eh mov bx, 07h int 10h ; BIOS Service func ( ah ) = 0Eh ; Write char as TTY ; AL-char BH-page BL-color jmp short T_38 T_39: _NO_: retn get_answer: xor ax, ax int 16h ; wait for keyboard command cmp al, 'y' je short _yes ; retry cmp al, 'Y' je short _YES_ cmp al, 'n' je short _NO_ ; exit cmp al, 'N' je short _NO_ cmp al, 'C'-40h je short _NO_ cmp al, 27 je short _NO_ jmp short get_answer _yes: mov al, 'Y' _YES_: retn T_40: ; write 2nd sector of FAT32 bs code (1024 bytes) mov byte [RetryCount], 4 mov byte [fattype], 0 mov bx, RD5_FAT32_hd_bs+512 cmp byte [lba], 0 jna short T_41 mov ax, [dosp_start] mov dx, [dosp_start+2] add ax, 2 ; sector 2 in the partition (after FSINFO sector) adc dx, 0 jmp T_33 T_41: ; convert FAT32 bootsector+2 address to CHS ;mov dl, [drv] ; drive ;mov dh, [_dh] ; head ;mov cx, [_cx] ; cl = sector, ch = cylinder (low 8 bits) mov ax, cx and al, 63 cmp al, [sectors] jnb short T_43 inc al cmp al, [sectors] jnb short T_42 inc cl inc cl jmp T_31 T_42: mov al, 1 ; sector 1 jmp short T_44 T_43: mov al, 2 ; sector 2 T_44: inc dh cmp dh, [heads] jb T_31 sub dh, dh ; head 0 shr cl, 6 xchg ch, cl inc cx ; next cylinder ;and cx, 1023 ;cmp cx, [cylinders] ;jnb short T_37 xchg cl, ch shl cl, 6 or cl, al jmp T_31 validate_primary_dos_partition: ; INPUT: ; si = partition table entry offset + file system ID ; OUTPUT: ; cf = 0 -> ah = primary DOS partition ID ; (01h,04h,06h,0Bh,0Ch,0Eh) ; al = FAT type ; 1 = FAT12 ; 2 = FAT16 ; 3 = FAT32 ; ; cf = 1 -> not a primary DOS partition sub al, al ; mov al, 0 mov ah, [si] cmp ah, 01h ; FAT12 partition jb short V_5 ; 0 je short V_3 V_0: inc al ; mov al, 1 cmp ah, 06h ; FAT16 CHS partition (>=32MB) ja short V_2 je short V_3 cmp ah, 04h ; FAT16 CHS partition (< 32MB) je short V_3 V_1: stc retn V_2: inc al ; mov al, 2 cmp ah, 0Ch ; FAT32 LBA partition je short V_3 ja short V_4 cmp ah, 0Bh ; FAT32 CHS partition jb short V_5 V_3: inc al ; 0->1, 1->2, 2->3 retn V_4: cmp ah, 0Eh ; FAT16 LBA partition jne short V_1 ;mov al, 2 V_5: retn ; ---------------------------------------------------------------------------- ; initialized data ; ---------------------------------------------------------------------------- align 2 retrodosv5bs: dw RD5_FAT16_hd_bs dw 0 ;volume_id: ; dd 0 ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; FAT boot sector code ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; 03/05/2024 RD5_FAT32_hd_bs: incbin 'RD5HDBS3.BIN' ; 29/01/2026 RD5_FAT16_hd_bs: incbin 'RD5HDBS2.BIN' ; 20/04/2024 RD5_FAT12_hd_bs: incbin 'RD5HDBS1.BIN' ; 20/04/2024 ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ; messages ;- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - drv: db 0 ;sectors: db 0 ;heads : db 0 ;cylinders: dw 0 _dh: db 0 _cx: dw 0 RD5_Welcome: db 0Dh, 0Ah db 'Retro DOS v5.0 Hard Disk Boot Sector Update Utility ' db 0Dh, 0Ah db 'RDHDBOOT v5.0.260129 (c) Erdogan TAN 2018-2026' db 0Dh,0Ah db 0Dh,0Ah db 'Usage: r5hdboot ' db 0Dh,0Ah, 0Dh, 0Ah db 'Drive names: ' db 0Dh, 0Ah db ' hd0 or C: ..for primary dos partition on 1st disk ' db 0Dh, 0Ah db ' hd1 or D: ..for primary dos partition on 2nd disk ' db 0Dh, 0Ah db ' hd2 ..for primary dos partition on 3rd disk ' db 0Dh, 0Ah db ' hd3 ..for primary dos partition on 4th disk ' db 0Dh, 0Ah, 0 db '03/05/2024' db 0 RD5_Do_you_want: db 0Dh, 0Ah db "WARNING ! ", 0Dh, 0Ah db "(If you say 'Yes', MSDOS or WINDOWS will not be bootable on this disk !) " db 0Dh, 0Ah, 0Dh, 0Ah ;db "Do you want to update boot sector to TRDOS 386 v2 format ? (Y/N) " ; 03/05/2024 db "Do you want to update boot sector to Retro DOS v5 format ? (Y/N) " db 0 _yes_str: db 'YES ' db 0Dh, 0Ah, 0 _no_str: db 'NO ' db 0Dh, 0Ah, 0 RD5_PressKeyWhenReady: db 0Dh, 0Ah db 'Press Enter to write boot sector on disk hd' RD5_Drive: db '?. ', 0 RD5_disk_WrittenSuccesfully: db 0Dh, 0Ah ;db 'Boot sector successfully updated to TRDOS 386 v2 format...' ; 03/05/2024 db 'Boot sector successfully updated to Retro DOS v5 format...' RD5_CRLF: db 0Dh, 0Ah, 0 RD5_disk_NotReadyOrError: db 0Dh, 0Ah db 'Disk error or drive not ready ! ' zbyte: db 'Try again ? (Y/N) ' db 0 RD5_invalid_bootsector: db 0Dh, 0Ah db 'Invalid boot sector (not a valid FAT' fattype_str: db '16 fs disk) ! ' db 0 RD5_fatp_notfound: db 0Dh, 0Ah db 'MBR does not contain a primary DOS partition ! ' fattype: db 0 RetryCount: db 4 lba: db 0 align 4 CHS_limit: dw 0 ;dw 0 sign: dw 417 ; ---------------------------------------------------------------------------- ; uninitialized data ; ---------------------------------------------------------------------------- bss_start: ABSOLUTE bss_start alignb 4 sectors: resb 1 heads: resb 1 cylinders: resw 1 dosp_start: resd 1 dosp_size: resd 1 MBR: bootsector: resb 512 end_bss: