OS deving should be a bit easier to get started...

JJeronimo · Post by **JJeronimo** » Sun May 20, 2007 12:09 pm

mathematician wrote:Windows was written with the idea that it should be portable, but how many platforms has Microsoft actually ported it to? Apart from the 3% of the market claimed by the Mac, the PC standard rules in the world of desktop computers, that's the point, and portability is a non-issue.

No! Portability is necessary. You can't think that way...
And portability is more than just being able to easily get the OS to run on another architecture. It's closely linked to extensibility. If your kernel architecture is able to adapt to any page size, for example, it's a good start.

For example, I consider that being able to use CPU features that are specific from some particular version of a CPU architecture (without breaking compatibility with other versions) is a portability issue.

And don't say that you will never be porting your OS to something different, because if today you write something that will run specifically on x86 Protected Mode, then you will run into problems when you try to make it take advantage of x86-64 Long Mode...
And if you don't design it correctly, then you may be unable to port it without breaking compatibility with PM-only CPUs.

JJ

mathematician · Post by **mathematician** » Mon May 21, 2007 2:57 am

If you were writing a segmented OS a few years back, you would need to have been psychic to have known that AMD/Intel were going to knacker the segment registers in a few years time. In fact OS/2 is going to face precisely that problem, unless they dropped segmentation in later versions of their OS.

Candy · Post by **Candy** » Mon May 21, 2007 2:26 pm

mathematician wrote:If you were writing a segmented OS a few years back, you would need to have been psychic to have known that AMD/Intel were going to knacker the segment registers in a few years time. In fact OS/2 is going to face precisely that problem, unless they dropped segmentation in later versions of their OS.

I was intending on making a segmentation + paging OS like OS/2 until both Intel and AMD announced (for AMD64 and IA64 back then) that they were going to drop segmentation. I played with the "screw them" idea for two weeks and then dropped segmentation.

JJeronimo · Post by **JJeronimo** » Mon May 21, 2007 3:41 pm

Candy wrote:I was intending on making a segmentation + paging OS like OS/2 until both Intel and AMD announced (for AMD64 and IA64 back then) that they were going to drop segmentation. I played with the "screw them" idea for two weeks and then dropped segmentation.

You have still FS and GS...

JJ

Candy · Post by **Candy** » Mon May 21, 2007 3:53 pm

JJeronimo wrote:
Candy wrote:I was intending on making a segmentation + paging OS like OS/2 until both Intel and AMD announced (for AMD64 and IA64 back then) that they were going to drop segmentation. I played with the "screw them" idea for two weeks and then dropped segmentation.
You have still FS and GS...

JJ

You wouldn't guess what the first thing was I made? Thread-local storage using GS.