Posted By
Litwr
on 2016-01-09
13:45:06
|  Re: A mathematical demo
Sorry for the typo. This is 5150.
It looks like that plussiers like to underestimate the power of Plus/4. See http://www.cpcwiki.eu/forum/demos/a-mathematical-demo/msg117035/#msg117035 - Amstrad's ppl on the contrary see their computer a bit overestimated. 
This mathematical demo shows a bit surprising result about C128 - it has the effective frequency about 1.9 MHz, not 2 as written in Wikipedia.
The version of this demo for IBM PC (http://litwr2.atspace.eu/ibm-5150/ibm-5150.html) is not so well optimized as the versions for 6502 or z80. I am sure that it may be accelerated by 50%. However my tests with Xlife-8 show that the main advantage of 8088 is the hardware division. The number π calculation relies mostly on the division. The demo for 6502 and z80 uses an unpublished and very fast 32 bit by 16 bit division routine but it is 3-5 times slower than the ML div-instruction of 8088.
The mentioned tests also show that 8088 without division at 4.77 MHz is only about 20% faster than 6502 at 2 MHz . US market was closed for the fastest 6502 computers, CBM II, BBC Micro... There were 6502 @3MHz even at 1981... There was also a problem of slow RAM. IMHO the part of the power of 8088 was consumed by this slow RAM.
[UPDATE]
I've just optimized IBM PC version. So it is become "official" too. It became almost twice faster and gives 1000 digits for 40.4 seconds. Is it less shocking? :-) This shows that 8088 at 4.77 MHz is approximately 2 times faster than 6502 at 2 MHz and the often usage of the division lifts this ratio up to 4.
I also made a version for RT-11 OS for PDP-11. It is still not optimized. It gives 1000 digits during 21.8 seconds at MicroPDP-11/83 (CPU at 18 MHz).
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