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30 Nov, 12 tweets, 4 min read

here's the wire-wrapped prototype of the original IBM PC (5150) motherboard!

this thing just *screams* IBM. the yellow wire was IBM's standard prototyping/bodge wire. to strip the wire, just crimp it with pliers and it peels off like a banana.

see? just like 🍌

the square pads are very distinctive of IBM prototyping PC boards

IBM also had house part numbers on chips. these "239 2111" devices are actually 7474 TTL flip flops.

https://twitter.com/kenshirriff/status/1322585264695357441

take a close look at those RAM chips. they're actually dual-die MK4332 devices! this original prototype has 64K of RAM.

https://twitter.com/kenshirriff/status/1322585264695357441

the ROM chip has a paper label on it dated to December 1980. 🤔

but there's something that you don't see on this motherboard prototype: IBM SLT modules, like in this photo. that's because the team used off-the-shelf parts! this was controversial inside IBM at the time.

just to make things clear: i don't have access to this IBM PC prototype motherboard. the photos are from a paper (ieeexplore.ieee.org/document/58873…). but the other photos are from a different IBM prototype that i do actually have!

https://twitter.com/TubeTimeUS/status/1032066215647166464

and that is the prototype of a 4" disk drive (yes, 4 inch) that was being developed around the same time. details in this thread.

https://twitter.com/TubeTimeUS/status/1032066215647166464

at some point i really ought to reverse engineer the circuit board for that.

it would *also* be fun to reverse engineer the prototype PC motherboard, but i don't have that. perhaps Dr. David Bradley (aka Dr. Dave), who helped create it, knows where it is.

it would be interesting to see differences from the release version. the same goes for the BIOS code

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@TubeTimeUS

29 Nov

i'm happy to announce the release of my latest sound card, the Snark Barker MCA! this is a Sound Blaster compatible card designed for Micro Channel bus computers, including the IBM PS/2 family.

the full open-source design is available here: github.com/schlae/snark-b…

this is not a product that i plan to sell, but it is a design that technically-inclined folks can fabricate.

fortunately, due to the permissive open-source license, others can fabricate and sell the cards!

https://twitter.com/TubeTimeUS/status/1299181646755708928

here's the epic design thread. this card was a lot of work to design and troubleshoot!

https://twitter.com/TubeTimeUS/status/1299181646755708928

Read 5 tweets

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@TubeTimeUS

5 Nov

here is part of the payload electronics from the Explorer 8 satellite (1960)! look at all the machined phenolic, colorful hand-tied wiring harness, and the stacks of round circuit modules! 🧵

there were apparently two of these columns of electronics. someone's taken apart the second column and we can have a look at some of the modules inside. they are *glorious* 🥰

i was expecting Explorer 8 to look pencil-shaped but it actually has this sort of bulge in the middle. i can't find a diagram showing how the stacked electronics were placed inside.

Read 35 tweets

Tube Time

@TubeTimeUS

23 Oct

this Tesla SUV ran into a traffic barrier at 70mph while on Autopilot. how could this happen? there are 3 major contributing causes, and they're *fascinating*

before we dig into the causes, let's set the scene first: the southbound 101 freeway at the intersection of 85. there is a left exit ramp so commuter-lane traffic can get to the 85 southbound commuter lane.

the Tesla was in the commuter lane, then departed that lane and headed into the strip of roadway (called the "gore") leading up to the median, crashing into the barrier.

Read 37 tweets

Tube Time

@TubeTimeUS

20 Oct

this ought to take a while to print.

not too shabby

that took 7 hours to print 😂

Read 4 tweets

Tube Time

@TubeTimeUS

18 Oct

in 1990, a tiny company nobody had heard of, Cadtrak, sued Commodore for patent infringement and won. Their company CEO bragged that he put Commodore out of business! Commodore's downfall took more than just that, but who was Cadtrak, and what was their patent? 🧵

first, the patent. 4,197,590, filed in 1978. it described a method for drawing a cursor and then erasing it again without having to store a copy of the background. this was a simple XOR operation.

you see, with an XOR, a '1' bit in the cursor caused whatever graphics were on the screen to get inverted. XOR it again with the same bit, and it gets inverted back to the original state. a '0' bit made no change. this saves RAM, since you don't need to keep a backup image.

Read 25 tweets