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I am trying to boot my own program from a floppy (like a MS-DOS bootdisk) so I write a little x86 assembly program (a .com file) and use a program rawrite to write it to a floppy.
I supposed this would work because .com files are simply an image of the code (unlike .exe's).
But when I try booting my computer with that floppy it simply stops (or hangs) at the point where it tries booting the floppy.
Where is the boot sector? you don't say what OS you are using, but I would have expected to have to create a bootable floppy first. From what you have sais, all you have done is copied your program?
Cheers
Why should it matter what OS I'm using?
I don't want to create a bootable floppy with dos on it.
I want to make a bootable floppy with my own program (call it operating system if you like).
Ah! I understand :)
Can you try the floppy on a Win98 or ME machine, it may give you a message.............the OS you are using for your experiment is of interest, as that might help me have a go at it.
I was always under the impression that a boot disk had to be set up as "bootable" or it would not be read any further than the boot sector bit............I could be wrong of course.
Cheers
Yes, I have tried (win98), that's were it hanged.
I tried something else now, I used 'sys' to make a bootdisk and replaced command.com with a copy of my own program (hello world). Now it booted but it said to enter the path/name of a command interpretenter instead of running my program.
I wrote my program as an image the first time heh. Do I have to make a custom bootsector for the first 512 bytes and only after that write the program itself?
Maybe try changing it to bootable with cfdisk?
Hi,
It is a VERY long time since I wrote a startup/boot disk, but I believe that what you say is more or less true..............at least you have received a response, rather than an invalid media message :)
I would have thought that you would need some sort of command interpreter, otherwise how will it know how to execute your program.
I am basing that on Windows installation disks and the diagnostics installation disks that come with hard drives. I know that CDs use "autorun" or whatever but I have never investigated it.........way after my time.........I am an old fart remember :D
How does it know how to execute that command interpretenter then?Quote:
I would have thought that you would need some sort of command interpreter, otherwise how will it know how to execute your program.
The thing I tried the second time is defintly not what I want to try.
I actually want to write an OS (well, actually a program that boots like an OS, not an OS really).
How the hell do you boot it then (floppy)?
As I recall, they usually boot up to a command line prompt. Try creating a Win98 boot disk and check out what is on that.
I will have a look at some of my old boot disks and see what I find. I am wondering what you want to do once you have booted with this disk..............like load CD drvers or whatever?
Cheers
EDIT: This article deals with the missing command line interpreter:
http://www.computerhope.com/issues/ch000012.htm
OTHER INTERESTING LINKS:
http://www.bootdisk.com
http://www.startdisk.com
http://www.computerhope.com/boot.htm
Obviously, it thinks the command.com is corrupt here as I replaced it.
I don't want to do anything specific, I simply want to run a program without an operating system (making it an operating system itself...sort off...you know what I mean).
I think so,
You would boot into a command line prompt.
You would have a command line interpreter (sort of runtime version of your CL).
You would have commands that you wanted
You would have any drivers needed (CD for example)
You would have any command utilities you needed (chkdsk, fdisk etc)
In other words, what you would have on a diagnostic/trouble shooting disk?
If you look at those links, you will see that most common boot disks are OS dependent. This is to keep them small and because they are for OS specific problems and tasks. On the other hand, the disks that come with hard drives (Caldera DOS for example) are not.
Cheers
Lol, I don't want to write some command line interpretenter that runs in dos or something.
The point is simply knowing how to write the most basic operating system.
My problem is simply not knowing how to get it to run make independantly.
I once found this proggie called 'Easy OS', it was simply a command interpretenter (not relying on any other os) written in assembly (obviously) and then it was written to floppy using some other program.
I feel like you are not understanding what I want to do...o_O.
No, I am only using DOS as an example. It is part operating system and part command language, so is probably not a good example, but is the one most commonly associated with "boot disks"
Say you wrote your OS in assembly, you would need a runtime assembly command interpreter to get the commands to execute. In this case assembly is merely the language you chose to write your OS in.
Perhaps a better example would be the old floppy boot sector viruses? Boot from an infected floppy and the virus would run.
In your case all you want it to do is display a command prompt?
Something like that?
Yes, the virus example is good.
I firstly only want to display a simple string to make sure it actually works, then write a command interpretenter. But that's not the problem, I should technically be capable of writing a command interpretenter in assembly.
You're a bit over my head here writing your own assembler, but from a working knowledge of 98 and dos I'll offer this - maybe it will help a bit.
When dos boots, it first looks for a file named 'command.com' - always. If it doesn't find it, it asks the user for it. I would suggest trying renaming your program 'command.com' on the floppy and see what good ol Dos spits back at you. Now, if you've written your own o/s, (unlike MS when they wrote win95/98/me and based it off of dos 6.0 and 6.2) this will (obviously) be different unless you've used Dos as a basis.
I wish you luck!
That's what I did, rename it to command.com but it said it wasn't a command interpretenter.
You sayI know, but how does the computer know how to boot dos? (from a floppy that is).Quote:
When dos boots, it first looks for a file named 'command.com' - always.
huh? The assembly is already assembled heh, to a binary file. /me is confusedQuote:
Say you wrote your OS in assembly, you would need a runtime assembly command interpreter to get the commands to execute.
Those particular instructions are burned into cmos - they read (in plain english)Quote:
I know, but how does the computer know how to boot dos? (from a floppy that is).
You are a computer.
You have devices. Here are their locations and how to communicate with them but not interpret.
The instructions on how to interpret them are located somewhere on the device.
Boot from this device first, then try this secondary device in case your (l)user has them there.
Grab the instructions, no matter what they are, and load them into memory, and keep them there the entire time you're running.
Try to use the instructions to interpret the data on the drive. If they fail, let the user know what caused the failure and halt the system.
Hope this helps - missing command interpreter is a biggie. It's basically telling you that it can't find instructions for user commands contained within the file. To you it means that my suggestion didn't work and you might either A: try something else, or B: include command interpretations within your file.
No, they aren't, the BIOS simply looks for a valid bootsector on the disk which is in the process of being booted. That bootsector contains the code needed to continue booting the operating system.Quote:
Those particular instructions are burned into cmos - they read (in plain english)
Anyway, that doesn't matter anymore as I have accomplished my purpose, I have written a bootsector and raw written it to a floppy.
How come it only displays a 'B' instead of the entire string I want to print?Code:[BITS 16]
[ORG 0]
jmp start
msg db 'Booting a shitty program$'
start:
mov ax,0x7c0
mov ds,ax
mov si, msg
lodsb
mov ah,0eh ; output character on screen function
mov bx,0007 ; bl value = attribute (back/foreground colour), not sure what bh does though...lol
int 10h ;BIOS interrupt
ret
times 510-($-$$) db 0 ;we need to fill so the binary image will be 512 bytes
;$ = start of instruction
;$$ = start of program
dw 0xAA55 ;fills last 2 bytes with 0xAA55 which makes this a valid bootsector
;(the BIOS checks whether it ends with 0xAA55)
Obviously I was being stupid again, it requires looping which we can accomplish:
/me wonders why the string is displayed 9 times????Code:[BITS 16]
[ORG 0]
;16-bit real mode
jmp start
msg db 'Booting a shitty program',13,10,0
displaymsg:
lodsb ; load si string into something else
or al, al
jz return
mov ah,0eh ; output character on screen function
mov bx,0007h ; bl value = attribute (back/foreground colour), not sure what bh does though...lol
int 10h ; call BIOS
jmp displaymsg
return:
ret
start:
mov ax,0x7c0
mov ds,ax
mov si,msg ; display message
call displaymsg
times 510-($-$$) db 0 ;we need to fill so the binary image will be 512 bytes
;$ = start of instruction
;$$ = start of program
dw 0xAA55 ;fills last 2 bytes with 0xAA55 which makes this a valid bootsector
;(the BIOS checks whether it ends with 0xAA55)