Am 22.01.2014 23:19, schrieb Orchid Win7 v1:
> On 22/01/2014 04:54 PM, Warp wrote:
>> Orchid Win7 v1<voi### [at] devnull>  wrote:
>>> Next up: Why, in the year 2014, am I still running installers that have
>>> 16-bit dithered logos? WTF?
>>
>> Obviously you need to be able to run it in safe mode...
>
> I didn't think even Safe Mode runs in 16-bit colour any more. And even
> if it does... so make the OS convert from 24-bit down to 16-bit on the
> fly! Sheesh.
>
>> Speaking of which, even though the 80386 processor was introduced
>> in 1985 (that's almost 30 years ago), PCs still boot up in 16-bit
>> mode. Yes, even the new 64-bit ones.
>
> I got the impression that 64-bit CPUs cut back on some of the really
> ancient 16-bit stuff. (I don't have an actual site for that though.)

That might well be. After all, you could emulate them via unknown-opcode 
traps.


>> The very first thing that the OS does is to switch to either 32-bit
>> mode (if the CPU is that old) or to 64-bit mode. After that it will
>> usually never revert back to 16-bit mode ever again.
>
> Ah yes - by toggling line 20 on the address bus. Obviously. (WTF?)

No, no - that A20 line thing is just for a small detail of the 16-bit mode.

> Well, that's only in so-called "IBM PC-compatibles". (How compatible are
> any of these with the 30-year old dinosaur?) I think the Apple Mac does
> it differently...

I'd be surprised if Macs came without A20 line gate. After all, it's the 
type of logic that's needed for IBM PC-compatibility but has been moved 
from discrete gates on the mainboard into the chipset decades ago already.


> Overall, PCs are just *full* of this crap. (Some of you may remember I
> once set out on a misguided quest to "write my own OS". I read up on
> some of this stuff.) And yet, when somebody produces a technically
> superior system that lacks lashings of backwards compatibility, nobody
> actually buys it...

... because of that very lack of backwards compatibility.

Actually, MS-DOS - and probably the IBM PCs as well - wouldn't have had 
any chance of success in the first place, had it not been for MS-DOS's 
backwards compatibility with CP/M at the application programming level.

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