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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: Re: [OSDev] How to switch to long mode in x86 CPUs?
Date: Tue, 4 Mar 2025 20:27:43 +0000
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On 04/03/2025 18:31, Paul Edwards wrote:
> "bart" <bc@freeuk.com> wrote in message news:vq208q$re74$1@dont-email.me...
>> On 02/03/2025 08:22, Paul Edwards wrote:
>>> "Scott Lurndal" <scott@slp53.sl.home> wrote in message
>>> news:JdFwP.46247$SZca.36276@fx13.iad...
>>>> "Paul Edwards" <mutazilah@gmail.com> writes:
>>>>> "David Brown" <david.brown@hesbynett.no> wrote in message
>>>>> news:vprtt6$3jah9$1@dont-email.me...
>>>>>> On 27/02/2025 16:57, Ar Rakin wrote:
>>>>>
>>>>
>>>>> Do you consider the concept of a BIOS (as seen as the IBM PC),
>>>>> "legitimate to use"
>>>>
>>>> In the abstract, possibly.  But the last half century has
>>>> shown that BIOS as an I/O abstraction layer was a bad idea
>>>> from the start.
>>>>
>>>>> and do you consider MSDOS (which uses that
>>>>> BIOS) to be an operating system?
>>>>
>>>> No, MSDOS was, is, will always be a simple program loader.
>>>
>>> Plus manages memory.
>>
>> How does it do that? I seem to recall that you got 640KB minus whatever
>> the resident parts of the OS needed.
> 
> Yes - and? Then you need to manage that memory, so you
> need a memory manager, which MSDOS provides. It's not
> trivial to write/debug one of those either.
> 
> I'm not sure what your question is exactly, so I'll include code
> to call the interrupt (21H AH=48H) you need to obtain memory.

I was questioning whether MSDOS provided means to manage memory, since I 
don't recall anything like that. My programs handled their own memory as 
they did most other things.

This 0x48/48H syscall is new to me.

(But it also looks like something it wouldn't use anyway, since it 
appears to work like malloc in storing the allocated size. That's 
something I would never need, and would be wasteful with the limited 
memory available.

Because I will either know the fixed size of the object I want to freed, 
or would need to keep a record of it anyway if it's more dynamic.)