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Z80 vs 8088 speed

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Nils M Holm

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Nov 12, 2023, 12:26:13 PM11/12/23
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Just compiled my T3X/0 compiler on an 8088 @ 4.77 MHz under DOS
and was surprised to see that it takes only slightly less time
than on an Z80 @ 4MHz under CP/M. See http://t3x.org/t3x/t3x0.html

I would have guessed that the 8088 is much faster at about
the same clock speed, because it has more 16-bit operations
and does multiplication and division in hardware. Of course
the compiler back ends also play a role, but the Z80 backend
typically emits *more* instructions for the same program.

I have never used an 8088 back in the days. In case you have,
what was your experience? Any technical explanation for my
results?

--
Nils M Holm < n m h @ t 3 x . o r g > http://t3x.org

Dennis Boone

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Nov 12, 2023, 2:23:19 PM11/12/23
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> I would have guessed that the 8088 is much faster at about
> the same clock speed, because it has more 16-bit operations
> and does multiplication and division in hardware. Of course
> the compiler back ends also play a role, but the Z80 backend
> typically emits *more* instructions for the same program.

The 8088 gives up a substantial portion of any 16-bit advantage to its
8-bit external bus.

De

Zbig

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Nov 18, 2023, 7:25:51 AM11/18/23
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> The 8088 gives up a substantial portion of any 16-bit advantage to its
> 8-bit external bus.

Not just that: https://trixter.oldskool.org/2011/06/04/at-a-disadvantage/

Quick, without doing any research: What early 1980s computer was faster,
the IBM PC or the Commodore 64? The IBM PC ran an 8088 at nearly 5MHz,
whereas the C64 ran a 6502 variant at 1MHz. The PC cost thousands of dollars,
the C64 hundreds. The PC had a 1 megabyte address space; the C64 only 64K.
Is this a trick question?

It is! The C64 was faster. [..]

Nils M Holm

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Nov 19, 2023, 6:41:51 AM11/19/23
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Interesting! So the real surprise is that the 8088 at about the same
clock speed is almost as fast as the Z80.
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