Booting from a primary FAT16 partition
; MenuetOS Boot Loader for FAT16 ; ................................. ; originally by John S. Fine johnfine@erols.com ; ; Adapted by vhanla for MenuetOS or Kolibri ; ; Notice that !!! ;................. ; I put the KERNEL.MNT into the FAT16 partition just for loading ; the kernel... but the kernel BOOTCODE needs to have the entire ; MenuetOS floppy image loaded into memory and that's where this ; bootloader fails... because this bootloader only gives control ; to the kernel.mnt. So, you need to have MENUET.IMG in the first ; primary FAT32 partition that has this file ("c:\menuet.img") or ; MSETUP.EXE ("c:\msetup.exe") it depends on KERNEL.MNT ; if you use KOLIBRI OS, MENUET.IMG is needed and if you're using ; official MENUET OS distro you need MSETUP.EXE in root directory ; ; WARNING!!! ; ----------- ; Since bootsector of a partition must be treated carefully, I ; recommend NOT TO OVERWRITE BYTES BEFORE! OFFSET 62 (3Eh)IN BOOTSECTOR ; NOTICE ALSO THAT IF THE FIRST 3 BYTES OF BOOTSECTOR DON'T MATCH ; THIS BOOTLOADER'S FIRST 3 BYTES, YOU NEED TO MODIFY THEM TO MATCH. ; THEN AFTER OFFSET 61 (3Dh), i.e., STARTING FROM OFFSET 62 (3Eh) YOU MUST ; REPLACE ALL BYTES INTO ALL BOOT SECTOR (512 BYTES SECTOR IS NEEDED) ; UNTIL OFFSET 512 ;) ; ; Do it carefully with your favorite hex editor ; ; PS: I TESTED THIS BOOTLOADER ONLY WITH MY 4GB SIZE HARD DISK ; I DON'T KNOW ABOUT LARGER HARD DISKs ; ; PS2: IT'S RECOMMENDED TO HAVE A BACKUP OF THE PARTITION BOOT SECTOR ; AND ALSO THE OFFSET NUMBER WHERE IT LOCATES IN THE PHYSICAL HARD DISK ; JUST TO KNOW WHERE TO RESTORE THE BOOT SECTOR IF SOMETHING WEIRD HAPPENED ; ;,,,,,,,,,,,,,,,,,, ; ... BE CAREFUL... THIS IS ONLY FOR FAT16, FAT32 HAS MORE SPACE FOR ; PARTITION INFO, SO REPLACING AFTER OFFSET 62 (3Eh) IN A FAT32, WILL CAUSE ; DAMAGES TO YOUR PARTITION STRUCTURE... ; I REPEAT !!!!! ONLY FAT16 --- SO TAKE CARE ; Features: ; ---------- ; CPU: Supports any 8088+ CPU ; ; Volume Format: Supports Only FAT16 ; ; Sector Size: Supports Only 512 bytes per sector. ; ; release date 04/02/2006 ; IV) Customization ; ; The memory usage can be customized by changing the _SEG variables (see ; directly below). ; ; The file name to be loaded and the message displayed in case of error ; may be customized (see end of this file). ; ; The ouput values may be customized. ;_____________________________________________________________________________ ROOT_SEG =0x800 FAT_SEG =0x800 IMG_SEG =0x1000 ; The following defined directives declare the parts of the FAT16 "DOS BOOT ; RECORD" that are used by this code, based on BP being set to 7C00. ; sc_p_clu equ bp+0Dh ;byte Sectors per cluster sc_b4_fat equ bp+0Eh ;word Sectors (in partition) before FAT fats equ bp+10h ;byte Number of FATs dir_ent equ bp+11h ;word Number of root directory entries sc_p_fat equ bp+16h ;word Sectors per FAT sc_p_trk equ bp+18h ;word Sectors per track heads equ bp+1Ah ;word Number of heads sc_b4_prt equ bp+1Ch ;dword Sectors before partition drive equ bp+24h ;byte Drive number org 0x7C00 entrada: jmp begin nop ; Skip over the data portion of the "DOS BOOT RECORD". The install method ; must merge the code from this ASM with the data put in the boot record ; by the FAT16 formatter. ; times 0x3B db 0 ; THIS PART IS THE PARTITION INFO AREA THAT YOU NEED ; TO CHANGE WITH YOUR PARTITION INFO begin: xor ax, ax mov ds, ax mov ss, ax mov sp, 0x7C00 mov bp, sp mov [drive], dl ;Drive number mov al, [fats] ;Number of FATs mul word [sc_p_fat] ; * Sectors per FAT add ax, [sc_b4_fat] ; + Sectors before FAT xchg ax, di ;DI = Sector of Root directory mov bx, [dir_ent] ;Max root directory entries dec bx shr bx, 4 inc bx ;BX = Length of root in sectors mov ax, ROOT_SEG ;Segment for root directory mov es, ax call read_16 ;Read root directory push di ;Sector of cluster two sc_clu2 equ bp-2 ;Later access to the word just pushed is via bp mov dx, [dir_ent] ;Number of directory entries xor di, di ;Point at first directory entry search: dec dx ;Any more directory entries? js error ;No mov si, filename ;Name we are searching for mov cx, 11 ;11 characters long lea ax, [di+0x20] ;Precompute next entry address push ax repe cmpsb ;Compare pop di jnz search ;Repeat until match mov si, IMG_SEG ;Segment for image push si ; segment for retf push bx ; zero offset for retf push word [es:di-6] ;Starting cluster number if FAT_SEG-ROOT_SEG mov ax, FAT_SEG ;Segment for FAT mov es, ax end if mov di, [sc_b4_fat] ;Sector number of FAT mov bl, [sc_p_fat] ;Length of FAT (or zero if FAT is 256) cmp bl, 0x81 ;If it is 1 through 0x80 js .1 ; then read it in one chunk push bx ; but for 0, or 0x81 through 0xFF mov bl, 0x80 ; read 0x80 sectors first. call read_16 pop bx sub bl, 0x80 ;Remainder after first 0x80 sectors mov ax, FAT_SEG+0x1000 ;Segment for second part of FAT mov es, ax .1: call read_16 next: ;Loop for all clusters pop ax ;Cluster number ; cmp ax, byte -0x12 ;End of file? cmp al, -0x12 jae eof ; Yes mov di, ax shl di, 1 ;A two-byte entry per cluster mov dx, FAT_SEG ;Assume first half of FAT jnc .1 ; It is first mov dh, (FAT_SEG/256)+8 ;Second half of FAT .1: mov ds, dx push word [di] ;Cluster number for next time dec ax dec ax ;Current cluster minus two mov bl, [sc_p_clu] mul bx ; * sectors per cluster add ax, [sc_clu2] ; + sector number of cluster two adc dl, dh ;Allow 24-bit result xchg ax, di ;DX:DI = sector number mov es, si ;ES = destination segment mov ax, bx ;AX = cluster size in sectors mov cl, 5 shl ax, cl ;AX = cluster size in paragraphs add si, ax ;Precompute next segment call read_32 ;Read one cluster jmp next eof: retf error: mov si, errmsg ;Same message for all detected errors mov ax, 0xE0D ;Start message with CR mov bx, 7 .1: int 10h ss lodsb test al, al jnz .1 xor ah, ah int 16h ;Wait for a key int 19h ;Try to reboot read_16: xor dx, dx read_32: ; ; Input: ; dx:di = sector within partition ; bl = sector count (max 0x80) ; es = destination segment ; ; The sector number is converted from a partition-relative to a whole-disk ; (LBN) value, and then converted to CHS form, and then the sectors are read ; into ES:0. ; ; Output: ; di = input di + input bx ; bx = 0 ; dl = drive ; si, bp and seg regs unchanged ; other registers modified lea ax, [di+bx] ;Compute di+bx (needed by two caller's push ax ; of read_16) add di, [sc_b4_prt] ;Convert to LBN adc dx, [sc_b4_prt+2] xchg ax, dx ;AX = (high) LBN cwd div word [sc_p_trk] ; / Sectors per track xchg ax, di ;AX = (low) LBN ;DI = (high) track div word [sc_p_trk] ;AX = (low) track ;DX = sector-1 inc dx mov cl, dl ;CL = sector mov dx, di ;DX = (high) track div word [heads] ; / Number of heads mov dh, dl ;DH = head mov ch, al ;CH = (low) cylinder ror ah, 1 ;rotate (high) cylinder ror ah, 1 add cl, ah ;CL = combine sector, (high) cylinder mov dl, [drive] ;DL = Drive number xchg ax, bx ;AL = Sector count mov ah, 2 ;AH = Read command xor bx, bx ;ES:BX = address int 13h ;Do it jc error pop di ;DI = Input DI + Input BX ret errmsg db 10,"KERNEL.MNT NOT FOUND",13 db 10,"Press any key to reboot...",13,10,0 filename db "KERNEL MNT" ;11 byte name times 0x7c00+510-$ db 0 db 0x55, 0xAA ;2 byte boot signature

The future!
nice nice... we have so many bootloaders now, but shouldnt we start thinking of getting rid of the ramdisk? And read files directly from a folder on a fat32 partition ? I dont think this would be that hard :) PS: since we have a full floppy driver now in kolibri, we can do the same for booting from floppy..

This to me as always been menuet biggest asset, but also its biggest draw back. When you first try menuet the ramdisk works great to show you what menuet can do in the fastest way. But if you want to use menuet as a OS than the ramdisk slows loading of OS and makes it harder to work on programs. So keep ramdisk as a demo OS ver and make a users ver without ramdisk, but with floppy driver etc.