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Z80 – The 1970s Microprocessor Still Alive (2021)

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Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#71

Post by flohofwoe »

brucehoult wrote: post #62
flohofwoe wrote: post #7

Earlier quoted context omitted.

"Simple" is really not a word I would associate with the Z80 ;) The ISA is quite messy because of the backward compatibility requirement with the Intel 8080 (e.g. the Z80 had to fill undocumented gaps in the 8080 opcode encoding map with new instructions, four of which were prefix instructions to unlock additional instruction 'subsets' (DD/FD for replacing instructions involving the HL register pair with indexed addr…

> I still prefer programming the Z80 over the 6502 though :) I really don't. There are some few things you can fit into and get working fast in the Z80's A + 6 registers (IX and IY are not useful if speed is the aim), but for anything complicated the 6502's 256 Zero page locations — any pair of which can hold a pointer you can index off — is far superior. The Z80 is awful at accessing memory for anything other than a…

In the end, you could do memory load/stores with around 1 byte per microsecond on most home computers, no matter if 6502 or Z80. The Z80 did less work per clock, but was usually clocked 2..4x higher than 6502 based systems, which made up for the higher instruction cycle counts (the 2 MHz 6502 systems might have a slight edge against a 4 MHz Z80, but it wasn't night and day, and the C64 got away with its 1 MHz clock because the CPU was more or less just a controller for the various custom chips).

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#72

Post by spacedcowboy »

joshu wrote: post #59
spacedcowboy wrote: post #39

Earlier quoted context omitted.

> wonders how ARM did that Acorn co-founder Hermann Hauser famously joked that he gave the original ARM microchip design team two distinct advantages: no time and no resources. With no money for a large crew or complex hardware, the tiny core team had to keep the processor design exceptionally simple, which ultimately birthed the revolutionary RISC architecture. It also had to run in simulation on a BBC micro… Probab…

berkeley/stanford birthed risc. acorn was inspired by the berkeley risc i papers.

"The revolutionary RISC architecture" here is referring to "the ARM architecture", which is a RISC architecture. I wasn't claiming that Acorn invented RISC.

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#73

Post by librasteve »

booty wrote: post #43
librasteve wrote: post #17

Earlier quoted context omitted.

wonders how ARM did that - the MIPS R2000 came in at ~115k and the 80286 ~134k anyway - say you want 50% of the transistors for on chip RAM these days, then thats 100 billion / 50 thousand = 2 million ARM 1s clocking at say 3GHz 6e15 MIPS = 6 peta MIPS so if you could run code on it, you would get a 10,000x speed up ;-)

GREAT classic question (with a well-defined answer) In general, the reason why modern CPUs are so complex is because the gap in performance between CPU and memory has grown massively over time. In the old days, something like a 6502 was running nearly synchronously with RAM. That gap has grown massively over time; a modern CPU is orders of magnitude faster than RAM. So they have to jump through a lot of loops to avoi…

the von Neumann bottleneck

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#74

Post by librasteve »

dofm wrote: post #51
icelusxl wrote: post #37

Earlier quoted context omitted.

ARM1 has no cache memory, no hardware multiply and division, no MMU and no cache.

Yeah — even ARM2 has no divide, as far as I recall from my days with an A310.

Well even in deep pipelined FPUs (I'm thinking Weitek 1167 for example), the "divide" instruction is microcoded ... this chip had a full IEEE P764 64-bit single cycle barrel shifting MAC ... but divide was built via a special "3-bit and guess" kind of long division that was microcoded. MAYBE someone has built a hardcoded divider these days - but that would be a waste if good transistors in typical instruction mix.

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#75

Post by jacquesm »

JKCalhoun wrote: post #21
getfacl wrote: post #6

Tom Jennings, the creator of fidenet, is producing a nice modern Z80 computer[0] 0. https://www.ebay.ie/itm/206496219323

RC2014 is the real deal: https://rc2014.co.uk Why I have not picked one up yet… I think I just have a sweet spot for the 6502 and keep putting together KIM-1 kits. (EDIT: Finally after years, I just pulled the trigger on their Classic II kit.)

Their AI policy is interesting reading.

https://rc2014.co.uk/ai-policy/

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#76

Post by linker3000 »

roygbiv2 wrote: post #69
JKCalhoun wrote: post #21

Earlier quoted context omitted.

RC2014 is the real deal: https://rc2014.co.uk Why I have not picked one up yet… I think I just have a sweet spot for the 6502 and keep putting together KIM-1 kits. (EDIT: Finally after years, I just pulled the trigger on their Classic II kit.)

It's actually fairly easy and interesting to design your own z80 computer. I went from knowing about assembly and pcb design to a z80 computer with a serial interface and memory banking. Learnt a lot on the way an went on to build pcbs for other projects with the knowledge I had gained from that.

Yay, wirewrap...

https://codeberg.org/linker3000/Z80-Board

Re: Z80 – The 1970s Microprocessor Still Alive (2021)

#78

Post by parlortricks »

JKCalhoun wrote: post #21
getfacl wrote: post #6

Tom Jennings, the creator of fidenet, is producing a nice modern Z80 computer[0] 0. https://www.ebay.ie/itm/206496219323

RC2014 is the real deal: https://rc2014.co.uk Why I have not picked one up yet… I think I just have a sweet spot for the 6502 and keep putting together KIM-1 kits. (EDIT: Finally after years, I just pulled the trigger on their Classic II kit.)

I got 2 from here, https://smallcomputercentral.com/kits/ and then some additional boards from Tindie to turn it into an MSX. I have not had the chance to build them out yet, but very excited too.
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