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Index > OS Construction > Thank you to Bogdan and everyone who posted their OSes

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Joined: 07 May 2004
Posts: 105
ShortCoder 17 May 2004, 02:25
I would like to say that this forum proves to be an invaluable resource towards learning how to code your own OS. I had read up on protected mode and also the boot sequence/etc but wasn't brave enough to try it myself without at least a few example programs. True, I could have downloaded and read through the Linux kernel but it is too complex--not a good place to start. Plus I see no document which tells you which file is the start file (which contains the very first instructions to be executed), etc...which is a general problem I have with lots of open-source code---HUGE sources and WHERE do you start?

I mean I figured you assume code origin at 7C00h (unless it's a BIOS routine you are flashing in which then starts at FFFFh I believe) and then enable the A20 line (wasn't exactly sure how to do that but knew it had to be done) then set up the GDT, IDT and LDT structures and load those and then do something with CR0 (wasn't sure exactly which bits to set) then end the sector with 55AAh. I really enjoy and APPRECIATE very manageable code which does what it is supposed to and is small enough so you don't need to spend days trying to figure where to start and also which is contained entirely in a few source files and is therefore very concise and easy to deal with. Those example OSes are great learning tools!

I'm going to read over them a few more times to try to get this down better and build up my confidence and understanding (still too chicken to implement it myself yet). I think the biggest obstacle to OS construction would have to be the myriad of hardware devices. I mean, you have to make device drivers for everything and where to find the necessary specs that you would need? You can find some of it at http://www.wotsit.org (I love that resource!) but, really, it's complicated. Not to mention some companies won't give out their info for their hardware.

Good luck to everyone trying:)
Post 17 May 2004, 02:25
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