WI DOS Memory had been larger?

As we all know, the DOS memory built in to the software was only 640k, and an entire industry and body of expertise grew up to exploit this to the max, particularly gamers.

Ironically it was basically a random selection by Gates and Co., and could have been very different.

How has this affected computer development?

(I thought I already posted this but can't find it)
 
Well, it was based on the Intel 8088 having a memory adress bus of only 20 bits. If IBM hadn't tried to cut costs, and instead had used a full 8086, or a Zilog Z800 or Z8000, or Motorola 68000, the memory map could have been a full 16 meg, which would have meant 8-12 meg of theoretical main system RAM.
 
Well, it was based on the Intel 8088 having a memory adress bus of only 20 bits. If IBM hadn't tried to cut costs, and instead had used a full 8086, or a Zilog Z800 or Z8000, or Motorola 68000, the memory map could have been a full 16 meg, which would have meant 8-12 meg of theoretical main system RAM.
I once made a biting comment about the IBM choice of the kludged Intel processor to someone who had worked in the industry at the time (not, IIRC, for IBM, though). And he pointed out, a bit heatedly, that Intel had a fully developed 8087 math coprocessor, and that made it the only viable system for a business/science machine. Which was something I hadn't considered.

It was true that Motorola had various coprocessors, but they required glue logic and they hadn't really put together a package in the way Intel did.

Also, IBM didn't WANT the PC to be a powerful machine - that could have threatened their mainframe business. So for them the x86 architecture worked very well.

For programmers and computer users, not so much.

@Kalvan. No, the 8086 had the same address space of the 8088. It wasn't until the 80286 rather later that the address space expanded.

@Weaver. The DOS limitation was in no way shape or form random. The x86 processors had a maximum limit of 1MB address space. Some of that had to be reserved for the BIOS, Graphics, etc. The 640K number is a little random, but 640 or 780 or 512 wouldn't make MUCH difference. the hard limit was 1MB.


Personally, I think the IBM guys should have done a little more work on the mother board and gone with the 68000 series chips. (i.e. done the glue logic work, basically)


@Weaver. Remember that memory was EXPENSIVE back then. The first PCs had 16 or 64K of RAM. 640K seemed (to some, although to to me(!)) to be lots at the time.
 
It's a bit cliché, but at times, limitations can push creativity... if you see what was done with the NES, by example... A console who came out in 86 If I remember well, Japan side, and whose last game was in 94 or so...
 
One of the other things that people forget about a small address bus, is that it helps keep programs smaller both in memory and on disk. This is because every machine code instruction that access memory contains an address

On an 8088, mostly you're working with 16 bit addresses, within a segment

On a 68K, mostly you're working with 32 bit addresses.

If programs were 10% or 20% larger to accommodate this, it requires more memory, which was expensive back in the early 80s.

Maybe it's not enough of a difference to stop the PC being a success, but it would certainly have an effect on the memory industry, and on which features programmers choose to include or exclude from applications.
 
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