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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

#21

Post by astrange »

DigitalJack wrote: post #8
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.

Interesting use of the word flash here. It's a magnetic disk though, no flash chips, so you would just say write. I imagine the issue was a lack of working drives, and Alto systems to run them.

And "flash memory" itself can't be flashed anymore. Isn't it called that because you could erase an EEPROM with a light?

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

#22

Post by jacquesm »

astrange wrote: post #21
DigitalJack wrote: post #8

Earlier quoted context omitted.

Interesting use of the word flash here. It's a magnetic disk though, no flash chips, so you would just say write. I imagine the issue was a lack of working drives, and Alto systems to run them.

And "flash memory" itself can't be flashed anymore. Isn't it called that because you could erase an EEPROM with a light?

No, flash is called flash because of the speed, relative to other programmable memories that can be erased.

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

#23

Post by agumonkey »

rhardih wrote: post #18

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.

I somehow suffer from the software / hardware split. The more I master the former, the more I need to learn about the latter. This is a good series. Kudos to their dedication and success.

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

#24

Post by cpr »

raldi wrote: post #17

I love that the first boot screenshot at https://lh3.googleusercontent.com/-JB4VOj7FgnU/V-lCHIADrsI/A... says: Date and Time Unknown Oh, you poor sweet computer, if we told you the answer, it would blow your little mind.

Probably will crash if you told it correctly. You know, the old Y2K problem. ;-)

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

#25

Post by ChuckMcM »

Awesome!

All you need is the white lab coat and Gene Wilder's "It's alive!" in the background. Congrats on getting it to this point, as anyone who has brought up new systems for the first time knows, once you can get your central processor to load and run software of your choice, you can use it to tell you what it not working correctly and bring everything else up. It is always a total rush when the system boots for the first time. (or in this case, "boots again" :-))

I would be particularly keen to insure that the arrow keys work on the keyboard, as a lot of Altos were used to play mazewar and that was hard on the arrow keys.

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

#26

Post by kens »

tkinom wrote: post #19

What were the CPU/ ISA used in the Alto?

To the programmer, the Alto's instruction set is the same as the 16-bit Data General Nova minicomputer, with the addition of a few crazy instructions such as "copy character bitmap from font file to screen".

The Alto's CPU is built from a whole pile of TTL chips on three boards. The Alto's arithmetic-logic unit, like many computers of that era, uses 74181 ALU chips. The CPU runs a crazy multitasking microcode, with one of the tasks emulating the Nova's instruction set. The hardware manual refers to the "microprocessor", meaning the microcode processor, not a microprocessor chip since microprocessors as such were in their infancy at the time.

There's a picture of the Alto's ALU board in one of my earlier articles [1]. You can see the individual CPU registers, as they are made out of multiple latch chips. For all the details of the Alto's CPU, see the hardware manual [2].

1: http://www.righto.com/2016/06/y-combinators-xerox-alto-resto...

2: http://bitsavers.informatik.uni-stuttgart.de/pdf/xerox/alto/...

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

#28

Post by lisper »

chiph wrote: post #20
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)

Wikipedia has a detailed description of the hardware design:

https://en.wikipedia.org/wiki/Xerox_Alto#Architecture

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

#29

Post by baobrien »

simcop2387 wrote: post #11
makomk wrote: post #9

Earlier quoted context omitted.

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.

The FPGA disk emulator/interface isn't quite working yet.

http://www.righto.com/2016/09/restoring-ycs-xerox-alto-day-7...

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

#30

Post by 0x0 »

I'm trying to read the article on an iphone but every time I zoom out to see the full width article I get bounced over to an article about toothbrushes?!

For the better part of a minute I was wondering if they had monkey-patched the disk controller with an electronic toothbrush?!

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