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Subject: Re: A random thought about bitboards

Author: Tom Kerrigan

Date: 18:52:29 10/24/01

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On October 24, 2001 at 17:48:26, Tony Werten wrote:

>Could be. I'm quite sure though that's what they said about 32bits when the
>got
>16 bits, and about 64 when they got 32.
>
>People don't know what they want until there has been a big advertisement
>campagne explaining why they really need it. After that it goes fast.

There was a super-big need for 32 bit addressing.

Very few <= 16 bit chips have address spaces as wide as their datapaths.
Examples: the 8 bit Z80 had a 16 bit address space and the 16 bit 8086 had a 20
bit address space. These are pretty hacky architectures because they need
separate "sub-datapaths" to do addressing. Programming these chips is also hacky
because you need segments and near/far pointers and crap like that.

Most 32 bit chips are 32 bits all the way through and people get along with them
just fine, with no hacks or awkward programming tricks to increase address
space.

Basically, there was a big, obvious need for ~32 bit addressing, but never a
big, obvious need for > 32 bit addressing.

This is backed up by the fact that 64 bit CPUs are readily available and few
people use them.

There are definitely cases where you want > 32 bit addressing, but not many.
Remeber, 64 bits gives you 4 _billion_ times as much address space as 32 bits.

I don't expect to see 128-bit CPUs (or at least a need for them) within the
next, say, 30 years.

-Tom



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