
Restoring Y Combinator's Xerox Alto, day 2: Repairing the display - zdw
http://www.righto.com/2016/07/restoring-y-combinators-xerox-alto-day.html
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specialist
This effort is neat.

As a kid, I cobbled together one working Xerox Star from several partially
working abandoned units. My friend's mom was a master typesetter,
wordprocessor, and data entry ninja. She used the Star for her business. She
loved it.

First and last time I got to play with a Xerox. I had an Apple //e (bought
with my own money) at home and used WordStar (right?). After seeing the Star,
it felt like I was banging the rocks together. I still think its crazy how far
ahead Xerox PARC was for the time. (Ditto The Mother of All Demos.)

For some reason, technology preservation warms my heart. The same feeling I
got chatting with the folks at the Computer Museum who are restoring a
mainframe to working order.

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digi_owl
Best i can tell, many things were developed in R&D and on mainframes that is
being "rediscovered" today on desktop and laptop. This because the price to
performance on ICs have gotten to the proper point, and because computing was
at the time insular (or at least seems to have been).

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fit2rule
The computer industries go through cycles of amnesia. Every new generation of
comp-sci grads bears some responsibility for this amnesia->re-invention cycle
- by ignoring the lessons of "the previous generation, who are clearly
antiquated and out-dated by virtue of being 'old'", new grads put themselves
in the precarious situation of having to re-invent the very solutions they
were ignoring in the first place. This is a cultural phenomenon - a clash of
generation-based prejudice - and not at all technological.

Manage developers - and the hiring of such - for more than a decade and you
will see this pattern occurring. Youth gain amnesia through prejudice, and
then re-invent the technology they ignored in the process. This happens time
and again.

~~~
aeorgnoieang
There's also a economic explanation – the costs of learning about all of the
good pre-existing solutions is large.

~~~
fit2rule
Very good point!

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WorldMaker
It's easy to forget how "rocketpunk" CRTs were: High voltage anodes! Dangerous
chance of implosions and/or X-Rays!

Amazing to think it was only a few decades since where just about every
household had at least one CRT, if not just about one in every room. Sometimes
we forget the past was also a strange place.

~~~
13of40
I remember my dad explaining how the electron beam scanning worked when I was
about 8 or 9 and I totally didn't believe him until he showed me the magnet-
on-the-TV-screen trick... (And it just occurred to me that there are probably
some younger people here who haven't seen that one. You can probably find it
on YouTube if you don't have a CRT handy.)

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amyjess
I have fond memories of synchronized degaussing in high-school computer
science class.

We'd all open up the menus on our monitors and then select the degauss option
at exactly the same time. Made a big ol' noise with that one. Can't do that
with an LCD, unfortunately.

~~~
rbanffy
There was a time I had on my desk a 21 inch Sony CRT that degaussed every
monitor within 6 feet along with itself.

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kw71
The explanation of raster scanning in portrait mode reminded me of an
interesting peculiarity in some other equipment.

Some of the first HP test equipment with raster crt screens, had the displays
oriented in a landscape position, but the rasters were vertcal. So they
scanned from one side to the other instead of from top to bottom.

I wonder what the reasoning behind that was and how they dealt with that in
the framebuffer and character generator.

~~~
ScottBurson
I can top that. Back in 1973-4 I was running Fortran programs on a CDC 6400
via a remote batch terminal. It consisted of a card reader, a line printer,
and a console with CRT and keyboard. It was connected via a 9600bps modem -- a
rare device that I'm sure cost thousands of dollars back then.

Anyway, the CRT had a scan pattern I've never seen since. Instead of two
levels -- a fast horizontal scan nested inside a slower vertical scan -- it
had _three_ : there was a slow vertical scan (presumably 60Hz), a medium-speed
horizontal scan that happened once, not for each pixel row, but for each
_character_ row, and then a fast character-height vertical scan to draw the
character rows. So it drew each character row from left to right one pixel
column at a time.

The whole thing must have cost well into six figures. Nonetheless it was a
little flaky. Sometimes the video on the console would go out -- I found a
particular spot on the case where I could whack it with my hand and the video
would come back.

~~~
userbinator
That's interesting and an example of what tricks can be accomplished if your
hardware is far more integrated --- I'd guess that the scan order was designed
specifically to require the least amount of buffering/auxillary RAM, and also
keep the character framebuffer in a linear order. Constraints on character ROM
access probably played a part in this too --- the more common pattern of
scanning one row of each character in a line requires changing the addresses
of the framebuffer and character ROM far more often, while this "character-at-
a-time" scan probably means they could pipeline accesses to the framebuffer
and ROM.

~~~
kps
It sounds like a workaround for the RCA character generator patent.¹

¹
[http://www.google.com/patents/US3345458](http://www.google.com/patents/US3345458)

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FullyFunctional
As an owner of a vintage monitor (Zenith ZVM-121) in need of repair, this was
very interesting, thanks.

The combination of posting on HN and being in the Bay Area really gives this
restoration the best possible odds. Oh, and it doesn't hurt that the Alto is a
much beloved and pivotal piece of hardware.

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vvanders
Yeah, there's also a couple running ones out there. The one they have at the
Seattle Living Computer Museum was the highlight of my visit there.

If you're ever in Seattle I cannot stress how effing cool that place is.

~~~
13of40
I think there's a specimen in the Microsoft museum archives too. I saw it on a
tour of their warehouse about ten or fifteen years ago.

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mmastrac
There was some interesting conversation on the video-only submission a few
days back:

[https://news.ycombinator.com/item?id=11977215](https://news.ycombinator.com/item?id=11977215)

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heywire
Thanks for mentioning that the video had previously been submitted, I was
starting to think I had been to the future :)

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kens
I did put it right in the first paragraph of the article: "You may have seen
Marc's restoration video (below) on Hacker News".

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spiderfarmer
Can't they use a CRT rejuvenator for this tube? Or is that what he meant by
upping the current?

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ubercore
They mention that in the article, and ask if anyone in the Bay Area has a
rejuvenator they can use.

~~~
jonah
And a comment on the article mentions someone in the area who has one!

