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 PostPost subject: Porting UNIX 5 to i386        Posted: Tue Jan 08, 2008 7:23 am 
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First off, I know and understand that there is no way of actually porting software that was written for the PDP-11 to i386 architecture; that the registers and whatnot are all different. Ken Thompson told me that when I asked him.

What I am wondering is, if there might be a way of writing an extention to the BIOS of a computer so that it can translate PDP-11 code and references into i386, without having to load an emulator (from disk). Or might one, perhaps, be able to write a program that acts as a second BIOS, and is set up in the MBR of the bootable hard disk, which can act as the simulator?

The reason why I've been wondering this is because I've been looking at the SIMH PDP11 simulator, with UNIX 5 on it, and thinking it would be cool if something similar could be done; but using a proper filesystem (instead of an image), and having the emulator bootable.

I've most probably not explaiuned that at all well; but does anyone think that something like that might work?

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 PostPost subject: Re: Porting UNIX 5 to i386        Posted: Wed Jan 09, 2008 6:18 pm 
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marktuson wrote:
What I am wondering is, if there might be a way of writing an extention to the BIOS of a computer so that it can translate PDP-11 code and references into i386, without having to load an emulator (from disk).

The skills required to this would be near insane as it would require reading through decompiled ASM; not to mention actually writting the program. Furthermore, compatibility would be near impossible as motherboards even from the same manufacturer often use drastically different hardware...

marktuson wrote:
Or might one, perhaps, be able to write a program that acts as a second BIOS, and is set up in the MBR of the bootable hard disk, which can act as the simulator?

Traditionally this is refered to as an emulator 8-)

marktuson wrote:
The reason why I've been wondering this is because I've been looking at the SIMH PDP11 simulator, with UNIX 5 on it, and thinking it would be cool if something similar could be done; but using a proper filesystem (instead of an image), and having the emulator bootable.

Why do you insist on not using an image? With some success, you maybe able to emulate a normal HD as DECtape... Yet why not use an image?

marktuson wrote:
I've most probably not explaiuned that at all well; but does anyone think that something like that might work?

It is my belief that you probably have better things in your life to do :D. If this for some reason is not the case, then consider learning lots and lots of programing before even atempting this...

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 PostPost subject:        Posted: Thu Jan 10, 2008 5:17 am 
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The reason why I don't want to use the images is because it would feel more 'real' to me if it used an actual filesystem. What's more, it would add to the overall accomplishment :). Also, it would make it easier to install (assuming an installer can be written), because then it could be installed pretty much the same way as any other *NIX OS can be. It would also allow for external editing and copying etc.. of files that are on the filesystem.

My thoughts about writing the simulator to BIOS were pretty daft, yes, but it's an ideal I'd like to eventually get to. Perhaps a small partition could be used to keep a minimal version of a *NIX OS and the simulator (SIMH?).

While talking about how the simulator would work, I'd like to explain: as far as I know, the term emulator is only correct when being used to refer to a hardware-based emulator, eg. Microsoft SoftCard (z80), or some of the other emulators that are bought as a PCI card now, and slotted into the motherboard. A simulator will act as the target computer, but only based on software-based instruction conversion etc... Correct me if I'm wrong.

SIMH; is there a way to suppress all of the messages it displays? That would, obviously, be the simulator to use, since it's already there.

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