My first ambitious project was a Z80 assembler. The Z8000 (much later) was distinguished by being the last random-logic (not microcoded) microprocessor of it's day.
Z80 – The 1970s Microprocessor Still Alive (2021)
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Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#42Ironically (and sadly) the Z80 was discontinued not very long after this piece was published.
I'm sure clones are still being made.
It's still active as a mask for a more complex system on a single die. Even the support chips are available. The Juno project, orbiting Jupiter, had a Z80 compatible core for the radar signal processing.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#43Earlier quoted context omitted.
The ARM 1 only had 25,000 or so.
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 avoid simply idling 99.99% of the time while they wait for some new data or instructions from RAM. On-CPU cache memory is one answer. Branch prediction and speculative execution are others. As you may imagine, speculatively executing code based on branch prediction is very complex because you must roll back any side effects from that execution if your prediction turns out wrong.
Example:
# assume `i` is a value stored in main memory
if i == 42
j += 1
k -= 1
l = 666
else
z = 123
q = 5879873
That's why we can't just take an R2000 and scale it up to 3ghz. I mean, we could, but it wouldn't work very well unless we also had low-latency 3ghz main memory to pair with it.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#44Earlier 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…
> If the Zilog engineers would have been free to design their own ISA I'm sure they would have been able to come up with a much more elegant design. That's an interesting idea. They were previously part of the team that designed the 8080 so they must have been very familiar with the ISA and the design philosophy. I'm sure they'd be able to come up with improvements but how much more elegant it would have been is hard…
Making it even harder to say: the 8080 was based on the 8008. Even though the 8080 was based on the same instruction set as the 8008, it wasn't binary compatible. I assume that means the instruction encoding was different, which means those engineers probably did as much as the could to clean things up while designing the 8080.
Of course, the 8008's origins (along with the completely unrelated 4004) were outside of Intel. They were hired to design custom ICs. The 8008's architecture was dictated by a CTC terminal. While Intel designed the 4004, it was only intended to be used in calculators. Intel, and its engineers, probably put relatively little thought into microprocessor architecture until the 8080.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#45Earlier 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…
> If the Zilog engineers would have been free to design their own ISA I'm sure they would have been able to come up with a much more elegant design. That's an interesting idea. They were previously part of the team that designed the 8080 so they must have been very familiar with the ISA and the design philosophy. I'm sure they'd be able to come up with improvements but how much more elegant it would have been is hard…
They did eventually design their own clean-sheet instruction set for Z8000.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#46Tom 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 don't know -- I'm seeing a lot of corner-cutting in the board designs!
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#47Ironically (and sadly) the Z80 was discontinued not very long after this piece was published.
IIRC, only the classic 40-pin DIP Z80 was discontinued. The eZ80, which is fully compatible, is still in production.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#48A paragrap from the linked articale Z80 was the choice of a microprocessor for then home computers such as Radio Shack TRS-80, SORD M23P, M5, Sinclair ZX81, ZX Spectrum, KayPro II, and many other manufacturers.3 It was capable of running the CP/M operating system in most Z80-based PCs. Z80 had a reasonable share in the PC market until Intel revealed its 16-bit microprocessor in the mid-1980s. Z80 was very popular as…
Z80 also powered the whole MSX line of home computers, how could have he missed that?!?
Also mentioned the KayPro II but omitted the Osborne 1.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#49interesting to be reminded that an 8080 (8 bit datapath) took 4,800 transistors an Apple M5 Max is 100,000,000,000 transistors (ok it’s 18 CPU + 40 GPU cores) by comparison so 17 million 8080 equivalents
> so 17 million 8080 equivalents At, ballpark, 1000 times the clock frequency. It’s a pity we do not how to connect such a large number of tiny cores in a way so that it can perform meaningful work. One hurdle is that, even ignoring the insane amount of connections needed, it would not be possible to connect each of those cores to each other one because their address spaces are so tiny.
> It’s a pity we do not how to connect such a large number of tiny cores in a way so that it can perform meaningful work
Every so often someone reinvents the transputer, and it turns out not to be quite as good as mainstream multi-core CPUs, but the wheel must turn.
Re: Z80 – The 1970s Microprocessor Still Alive (2021)
#50Reminded me good old days.. games loaded from cassette recorder and my first program for Spectrum which was a simple drawing tool I proudly called "graphic editor" :)