Posted By
MMS
on 2015-01-05
15:04:00
 |  Re: World of Commodore 2014 pictures, video, reports
Z80 has no access to SID or VIC: like the Spectrum 
Still, C128 is the biggest success of any CP/M comaptible machine, sold 4 millions, despite high price.
Well, if CP/M dos65 would be available at that time, no need for Z80 in c128, would increase competitiveness on the market.
(less complicated architecture --> cheaper machine --> more sales --> bigger profit)
CP/M could also run way faster (2Mhz 8502 + VIC II).
But there are interesting limitations, seems to copy some Plus/4 weirdness.
8502 clocked down to 0.98Mhz and several badlines... You can run faster only if VDC enabled, but very hard to program, no BASIC commands at all, and for a long time no documentations at all...
BTW Z80 has no access to VIC, but has no bad lines too! So can have 2 times the memory access than 8502 in the same machine. BUT, to match to the memory speed, Z80 is said clocked down to 2MHz.
BTW there is a guy (seems reflecting on your speed comment) that 6502 is faster on 1MHz than the Z80 at 2 Mhz "LDIR/LDDR on Z80 take 21 cycles/byte, soy you can theoretically move ~95KB/second at 2MHz. LDA,X+STA,X+INX+BNE takes 14 cycles, resulting ~142KB/sec copy speed. With reasonable unrolling 8502 is faster even at 1MHz."
Memory is also an issue. Experts says CP/M bare minimum requirement is 32K, but probably OK with 48K.
CPC had 128K access. As I see, the Z80 in C128 can see one dedicated bank. tTat means 64k.
So it is not a big surprise, why a CPC with 4MHz+128K is faster than a 2Mhz Z80 + 64K in C128.
Too bad that C128 was more expensive. But still, there were some professional use for it's CP/M.
I do remember the big transport company my mother worked, used C128s to manage tarnsport records, in CP/M mode and some database program (first I was impressed, as from 3 meters it looked like an Amiga )
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