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Restoring YC's Xerox Alto day 8: it boots

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Re: Restoring YC's Xerox Alto day 8: it boots

#11

Post by simcop2387 »

makomk wrote: post #9
tiles wrote: post #6

This is an amazing milestone! I have to ask, why did we need a separate boot disk sent over instead of flashing the previous disk with the contents of a boot disk? I suppose swapping out parts is an expected part of restoration though.

They don't currently have any way of writing to the disk except using the Alto itself, which would require booting it first. Once they get it working they should be able to create their own boot disk.

They had that test jig in the previous video that could drive the disk and read it (and i think write it). That would have allowed them to do so, i would think, regardless of how slow it might have been.

Re: Restoring YC's Xerox Alto day 8: it boots

#12

Post by kens »

tiles wrote: post #6

This is an amazing milestone! I have to ask, why did we need a separate boot disk sent over instead of flashing the previous disk with the contents of a boot disk? I suppose swapping out parts is an expected part of restoration though.

We're building a FPGA-based disk emulator that we could connect to the Drive to rewrite the junk disk, but we don't have that ready yet. The Living Computer Museum could have rewritten our disk for us, but that would have required sending our disk to Seattle first so they just sent us a new disk. (The Living Computer Museum has been extremely helpful, so visit them if you're in the Seattle area!)

Re: Restoring YC's Xerox Alto day 8: it boots

#13

Post by raldi »

kens wrote: post #12
tiles wrote: post #6

This is an amazing milestone! I have to ask, why did we need a separate boot disk sent over instead of flashing the previous disk with the contents of a boot disk? I suppose swapping out parts is an expected part of restoration though.

We're building a FPGA-based disk emulator that we could connect to the Drive to rewrite the junk disk, but we don't have that ready yet. The Living Computer Museum could have rewritten our disk for us, but that would have required sending our disk to Seattle first so they just sent us a new disk. (The Living Computer Museum has been extremely helpful, so visit them if you're in the Seattle area!)

Their assistance was really shrewd; I've been to the CHM in Mountain View before, but had never heard of the LCM and probably would never have gone before this, but now I'm definitely going to go the next time I'm up in Seattle.

Re: Restoring YC's Xerox Alto day 8: it boots

#14

Post by kens »

cnvogel wrote: post #7
kens wrote: post #5

Earlier quoted context omitted.

We'll leave the probes on until we're done debugging since it's pretty tedious to reinstall them. Is there any particular reason you suggest booting without the probes?

Probably out of fear that the signals might deteriorate with probes attached. But with a modern-ish logic-analyzer and the ancient original hardware (huge voltage swings, slow clock, very long busses), I doubt that the probes would make a discernible difference, would they?

Yes, you're right about the signals. The Alto has a 5.88 MHz clock which is very slow by modern standards, and the buses are a couple feet of wire-wrapped pins so the probes are unlikely to have any effect.

I'm not sure modern-ish is the right word for the logic analyzer. It's a 1999 Agilent logic analyzer and I don't know how they managed to make it so slow. You can ftp a trace off it over Ethernet at the glacial speed of 10 kilobytes per second, so copying traces for analysis is a big bottleneck.

Re: Restoring YC's Xerox Alto day 8: it boots

#15

Post by kens »

raldi wrote: post #13
kens wrote: post #12

Earlier quoted context omitted.

We're building a FPGA-based disk emulator that we could connect to the Drive to rewrite the junk disk, but we don't have that ready yet. The Living Computer Museum could have rewritten our disk for us, but that would have required sending our disk to Seattle first so they just sent us a new disk. (The Living Computer Museum has been extremely helpful, so visit them if you're in the Seattle area!)

Their assistance was really shrewd; I've been to the CHM in Mountain View before, but had never heard of the LCM and probably would never have gone before this, but now I'm definitely going to go the next time I'm up in Seattle.

I don't think they're assisting because they are shrewd, but because they are genuinely nice and helpful people, and like to see old computers running.

Re: Restoring YC's Xerox Alto day 8: it boots

#16

Post by raldi »

kens wrote: post #15
raldi wrote: post #13

Earlier quoted context omitted.

Their assistance was really shrewd; I've been to the CHM in Mountain View before, but had never heard of the LCM and probably would never have gone before this, but now I'm definitely going to go the next time I'm up in Seattle.

I don't think they're assisting because they are shrewd, but because they are genuinely nice and helpful people, and like to see old computers running.

Oh, of course! I didn't mean to suggest otherwise. I'm just saying, it's also great publicity in addition to everything else.

Re: Restoring YC's Xerox Alto day 8: it boots

#18

Post by rhardih »

This series is the best thing on HN in a long time. As a software engineer by trade, I feel like I've been missing out not learning more about electrical engineering. The level of knowledge and skill involved in this restoration is downright awe-inspiring.

Re: Restoring YC's Xerox Alto day 8: it boots

#20

Post by chiph »

tkinom wrote: post #19

What were the CPU/ ISA used in the Alto?

This took place way before that technology existed. The CPU (ALU + Control Unit) was built from individual chips.

The Alto dates from 1973, and Intel's 4004 microprocessor dates from a year or two before (and was used to run a calculator, not a personal networked workstation)

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