A computer built from NOR gates: inside the Apollo Guidance Computer
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Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#2If you like this kind of thing I suggest watching Ben Eater on YouTube or his website.
Ben explains and builds basic computers from components. It's more to see how things work like registers and memory addresses. It's a nice mix of electronics and computer science.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#3If you like this kind of thing I suggest watching Ben Eater on YouTube or his website. Ben explains and builds basic computers from components. It's more to see how things work like registers and memory addresses. It's a nice mix of electronics and computer science. https://www.youtube.com/channel/UCS0N5baNlQWJCUrhCEo8WlA https://eater.net/
Ben is a godsend. I remember having my mind blown by his 8-bit microcomputer series after years of wondering "okay, I know how to program, and I know about assembly, but....what's after that?"
When I ended up taking a MIPS class not too long after, it felt more like a recap of Ben's material than anything new.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#4Back in the 1990s, UC Berkeley's computer hardware quals exam used to require the test taker to design a microcoded RISC processor out of NAND gates, from the bottom up. It was kind of like Little Alchemy, once you created every kind of primitive gate you needed, you could assemble them to make larger and larger things. This included building latches, registers, static RAM, bottom to top. NOR is just NAND with 0's and 1's reversed.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#5Back in the 1990s, UC Berkeley's computer hardware quals exam used to require the test taker to design a microcoded RISC processor out of NAND gates, from the bottom up. It was kind of like Little Alchemy, once you created every kind of primitive gate you needed, you could assemble them to make larger and larger things. This included building latches, registers, static RAM, bottom to top. NOR is just NAND with 0's an…
This is pretty much the approach I took a few months back after reading _But how do it Know?_ by J. Clark Scott, although I wrote it in software [1]
[1] https://medium.com/swlh/i-dont-know-how-cpus-work-so-i-simul...
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#6Back in the 1990s, UC Berkeley's computer hardware quals exam used to require the test taker to design a microcoded RISC processor out of NAND gates, from the bottom up. It was kind of like Little Alchemy, once you created every kind of primitive gate you needed, you could assemble them to make larger and larger things. This included building latches, registers, static RAM, bottom to top. NOR is just NAND with 0's an…
That is basically the premise of the awesome Nand2Tetris[0] book/project.
[0] https://www.nand2tetris.org/
Edit: Just saw that it is even referenced[1] in the article itself.
[1] https://www.righto.com/2019/09/a-computer-built-from-nor-gat...
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#7I was impressed to learn that when Margaret Hamilton programmed this machine, she wrote an interpreter, and coded the mission logic in the interpreted language. So, in a sense, it really was microcoded; but the microcode was what looks like the real instruction set, and the instructions actually used lived in ROM.
The Xerox Alto, which was used for the original Smalltalk in 1972, also worked much this way: It had 16 program counters, one of which pointed to a program for interpreting Alto instructions. Other program counters were for refreshing the screen, operating the disk, driving the laser printer, and moving network packets. An interrupt just changed which program counter instructions came from.
The Smalltalk runtime was another interpreter, interpreted by Alto (interpreted) instructions. People complained about how slow Altos were, no surprise.
I might have misremembered some of the details above. Corrections welcome.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#8Back when I was a CPU logic designer, I worked on two machines that used ECL logic, where the basic building-block gate was a 4-input OR/NOR (the gate produced both phases at output). I recall that on one of these machines, each logic card was supplied with well over 100A on the -4.5 supply, we had a space budget of 98 cards. But the tough limit to hit was cooling. For the entire CPU we had only a single 20 BTU-ton water chiller, and had to sneak everything in under the cooling limit.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#9NOR was used instead of NAND because the latter would've required a series connection of transistors, which changes the voltage levels needed and otherwise complicates the design.
Re: A computer built from NOR gates: inside the Apollo Guidance Computer
#10Back when I was a CPU logic designer, I worked on two machines that used ECL logic, where the basic building-block gate was a 4-input OR/NOR (the gate produced both phases at output). I recall that on one of these machines, each logic card was supplied with well over 100A on the -4.5 supply, we had a space budget of 98 cards. But the tough limit to hit was cooling. For the entire CPU we had only a single 20 BTU-ton w…
> For the entire CPU we had only a single 20 BTU-ton water chiller
We'll probably get there soon again, this time for gaming PCs.
Was this at one of the mainframe manufacturers?