
TROS: IBM mainframes stored microcode in transformers - magnat
http://www.righto.com/2019/11/tros-how-ibm-mainframes-stored.html
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aidenn0
Just a few years later, HP did 16 layer PCBs instead of the mylar tape and
achieved ROM that was very dense and fast for its time[1]; though apparently
yields were quite poor.

1:
[http://www.hp9825.com/html/the_hp_9100_rom.html](http://www.hp9825.com/html/the_hp_9100_rom.html)

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myself248
I've heard about program store sheets in the Bell System early electronic
computers, but I'm not sure how they compare to this. Never have found a good
explanation of how they worked, just a few of my older colleagues described a
stack of "memory sheets" they'd swap when it was time to change the computer's
programming.

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flyinghamster
The #1 ESS telephone switch's processor used two types of memory. Ferrite
sheets were used for read/write memory to store temporary data, in a manner
similar to magnetic core memory, while twistor memory was used for rewritable
but mostly read-only storage, to store the system programs.

[https://en.wikipedia.org/wiki/Twistor_memory](https://en.wikipedia.org/wiki/Twistor_memory)

[https://en.wikipedia.org/wiki/Number_One_Electronic_Switchin...](https://en.wikipedia.org/wiki/Number_One_Electronic_Switching_System)

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jcims
My stepdad worked for AT&T back in the 70’s/80’s. He took us to his office one
night and we saw an old ESS switch that had magnetic core memory. I just
started programming at the time but remember it creeping me out for some
reason.

We also listened in on a random phone call and called a small restaurant in
France to listen to the menu of the day.

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AstroJetson
So while we are in awe, there is some group of engineers that are going "hey
grandkid, let me tell you about Mylar memory. They pushed the envelope back in
the day. It would be nice if some of these articles would have names so we
could go "wow Bob, that was some amazing engineering".

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wil421
What’s Mylar memory? Is it magnetic core memory?

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gopalv
The article starts with

"This unusual storage mechanism used a stack of Mylar sheets to hold 15,360
bits, equivalent to 1920 bytes."

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wil421
Yes I know it even has a picture. My question is what is it?

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chiph
It's a sheet of Mylar that has had conductive traces deposited on it, forming
wires. This means it can be bent to go around curves without the use of
additional connectors.

The interesting thing to me about the TROS sheets is that they were initially
manufactured to be the same [0] but were programmed by punching out (cutting)
the traces in places to zig-zag the current path either through a transformer
loop or around it. Presumably there was a machine that positioned a punch to
the correct position, based on coordinates from an input punch-card deck,
before descending and cutting through the traces.

[0] Note that there are two designs - one with the inputs on the left and one
with the inputs on the right, to line up on the connector block to the diodes.
Although it's possible it's the same design, just flipped before the punching
step.

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wil421
Got it. When I saw the squares it reminded me of magnetic core memory. I
thought the squares were the punches but I can see it in this image[1].

[1] [http://static.righto.com/images/ibm-360-tros/tros-
diagram.jp...](http://static.righto.com/images/ibm-360-tros/tros-diagram.jpg)

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deelowe
Huh. Kind of similar to rope memory in function but packaged completely
differently.

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jascii
The article actually mentions that and compares the two: Rope memory has a
higher storage density (important for a spacecraft) while mylar TRO is easier
to change the programming (hole punch a stack of sheets vs threading a lot of
wire through cores)

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pacaro
TFA also notes that the roles of the wires in the two types of memory is
reversed

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agumonkey
As impressive as frightening.

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ddingus
What is the frightening part to you?

Sincere question. I am just curious for perspective. I like old tech and am
always interested in others general take on it.

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agumonkey
The amount of ingenuity and complexity and also a bit of "wildness" factor

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ddingus
Reminds me of pre digital music. Same things. Humans who knew their shit and
who presented raw skill, acumen.

Yeah. I get that.

What if we are somehow forced to return? Some disaster or other.

Will we still be those same quality humans?

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agumonkey
There's a bit of that in the pre digital eras. Things were much more complex
and strange. Before doing anything with electric systems you had to study
sophisticated mathematics. Now you can just get along with some arithmetics.

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ddingus
Old tech is cool to me because so much of it was human scale.

One can just see the parts. Love it.

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paulsutter
Can anyone find the speed of this memory?

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kens
TROS had a cycle time of 625 nanoseconds with an access time of 240
nanoseconds including address decoding and delays through the sense amplifier.

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ddingus
My Apple 2 has 100ns RAM. I am pretty sure slightly faster machines used 80ns.

This old memory speed seems fairly respectable for the time.

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blattimwind
GPIB, a bus system from the mid 60s, requires a response time of <100 ns to a
particular signal. That's one of the reasons why it's still practically
impossible to implement in software only 50 years later.

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ddingus
And we hit that on tech of the era too.

Damn cool.

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blattimwind
We had discrete logic in the late 60s that achieved toggle rates of a couple
hundred MHz (ECL), it was just kinda expensive and needed loads of power. It
was (and afaik still is) however widely used in aerospace/military
applications (high standing currents and low impedance transmission lines
probably make for excellent radiation and interference immunity) and used to
be common in high end high frequency test equipment (e.g. counter/timers,
synthesizers). I've heard ECL was also very popular for implementing
cryptographic devices due to its low noise / switching transients.

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butterisgood
More than meets the eye

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bitwize
I knew it! OS/360 was a decepticon plot all along!

