Ken Shirriff✓

Mastodon @kenshirriff@oldbytes.space

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Followers

11.4K

Account age

3 yrs

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The Space Shuttle had five general-purpose computers that controlled, monitored, and navigated the Shuttle. Each computer consisted of two boxes: the CPU (right) and the I/O Processor (IOP, left). The IOP connected the computer to 24 high-speed networks. Let's look at two boards from the IOP... 1/N

194 views The Space Shuttle had five general-purpose computers that controlled, monitored, and navigated the Shuttle. Each computer consisted of two boxes: the CPU (right) and the I/O Processor (IOP, left). The IOP connected the computer to 24 high-speed networks. Let's look at two boards from the IOP... 1/N

I dissolved the metal with acid so you can see the silicon circuits in the 8087 chip. The pinkish regions are doped silicon. The thin lines are polysilicon wires on top of the silicon. When polysilicon crosses doped silicon, it forms transistors, the switches that make circuits work.

44 views I dissolved the metal with acid so you can see the silicon circuits in the 8087 chip. The pinkish regions are doped silicon. The thin lines are polysilicon wires on top of the silicon. When polysilicon crosses doped silicon, it forms transistors, the switches that make circuits work. $For those who like schematics, here's four bits of the adder, reverse-engineered. It's too complicated to explain here, but for those who care: "Manchester carry chain" computes carries, along with a "carry skip" circuit. "F" is the input from the fraction bus and "prop" is the "propagate" value.$ 31 views For those who like schematics, here's four bits of the adder, reverse-engineered. It's too complicated to explain here, but for those who care: "Manchester carry chain" computes carries, along with a "carry skip" circuit. "F" is the input from the fraction bus and "prop" is the "propagate" value.

This diagram shows how the circuit boards (called pages) were plugged into the I/O Processor's aluminum-alloy case. For storage, the system used magnetic core memory, larger pages at the back. This system didn't use a microprocessor; it was built from 11 logic pages crammed with simple chips.

29 views This diagram shows how the circuit boards (called pages) were plugged into the I/O Processor's aluminum-alloy case. For storage, the system used magnetic core memory, larger pages at the back. This system didn't use a microprocessor; it was built from 11 logic pages crammed with simple chips.

📊 Post engagement

Avg engagement / post

0.4%

Engagement vs followers

Nov 2022

On Mastodon since

🔥 Top post: The Space Shuttle had five general-purpose computers that contro · 194 likes + reposts

📊 Activity & format

Posting cadence

5.6 / week

Posts several times a week.

Content mix

Mostly images

Recent: 3 text · 9 image · 0 video.

Follower / following

26×

Follows 442 back. A strong ratio — an audience that follows them, not a follow-for-follow network.

Recent posts

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🔥 Top post The Space Shuttle had five general-purpose computers that controlled, monitored, and navigated the Shuttle. Each computer consisted of two boxes: the CPU (right) and the I/O Processor (IOP, left). The IOP connected the computer to 24 high-speed networks. Let's look at two boards… ★ 194

Credits: IOP boards provided by Richard, 4 Pi board from @tubetime. Photo of the IOP and CPU courtesy of RR Auction. IOP documentation from Mike Stewart. Exploded diagram from https://ibiblio.org/apollo/Shuttle/IBM-74-A31-016%20-%20Space%2… ★ 16 Want more photos? Or more info, such as how the I/O processor implements 25 virtual processors with two instruction sets on top of a single physical processor? See my latest article: https://www.righto.com/2026/06/space-shuttle-io-processo… ★ 58

This diagram shows how the circuit boards (called pages) were plugged into the I/O Processor's aluminum-alloy case. For storage, the system used magnetic core memory, larger pages at the back. This system didn't use a microprocessor; it wa… ★ 29

IBM had a series of aerospace computers called System/4 Pi. These computers all used standard-sized boards (top). Except that the I/O Processor's boards (bottom) were one inch wider. I guess they needed the extra space for more circuitry. ★ 29

The second board is memory (PROM), holding microcode for the I/O Processor, which is a (very strange) computer, independent of the CPU. Each gold-lidded chip holds 2K bits in tiny metal fuses. The chip is programmed by blowing the fuse for… ★ 23

First board is a network interface. Each side is identical and supports two networks. The IBM hybrid module (right) contains tiny transistors, resistors, etc. to handle the analog stuff. The golden Motorola chips format bits to transmit an… ★ 28 For full details, see my latest article: https://www.righto.com/2026/06/intel-8087-adder-reverse-engineered.html A group of us, including @gloriouscow and Smartest Blob are reverse-engineering the 8087. ★ 72

For those who like schematics, here's four bits of the adder, reverse-engineered. It's too complicated to explain here, but for those who care: "Manchester carry chain" computes carries, along with a "carry skip" circuit. "F" is the input … ★ 31

The adder is part of a set of registers and shifters that make multiplication, division, and square roots fast. The 8087 multiplies two bits at a time (twice as fast) thanks to the Multiply Decision Box and selector. The Quotient Register … ★ 24

I dissolved the metal with acid so you can see the silicon circuits in the 8087 chip. The pinkish regions are doped silicon. The thin lines are polysilicon wires on top of the silicon. When polysilicon crosses doped silicon, it forms trans… ★ 44

For performance, the adder is constructed in blocks of four bits. Here's one block under the microscope. This shows the chip's single metal layer, the metal wiring on top of the silicon that connects things. Modern chips can have over 20 l… ★ 23

🐘 Community & instance

Home server

oldbytes.space

Their home server on the fediverse — the instance a creator picks signals the community they belong to.

✅ Link-verified

Verified link

Proved ownership of a website linked on their profile — Mastodon's green-check verification, a real identity signal rather than a paid badge.

On Mastodon since

Nov 2022

Joined in the Twitter-exodus wave of late 2022 — part of the migration that made Mastodon a real destination.

💡 Facts

🗓️Joined Mastodon in 2022 — 3 years ago.

👁️Averages 48 views per post.

📤Posts about 5.6× per week.

🏅Earned the 10K Followers for passing 10K followers.

🛡️ Audience credibility

81/100

Excellent Credibility score

97%

Real Real audience

Low Fake-follower risk

High Data confidence

Est. 97% real, active audience · Low fake-follower risk.
Engagement (~0.4% of followers engage each post) is around typical for Mastodon.
Organic base — far more followers than accounts it follows.
Verified account.
Established account (3+ years old).

Heuristic estimate from engagement, follower ratios, account age & growth — a screening signal, not a guarantee.

About

Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Xerox Alto. Ex-Google, Sun, Msft. So-called boffin.

📸 Gallery

$For those who like schematics, here's four bits of the adder, reverse-engineered. It's too complicated to explain here, but for those who care: "Manchester carry chain" computes carries, along with a "carry skip" circuit. "F" is the input from the fraction bus and "prop" is the "propagate" value.$

🔀 Audience overlap

Estimated

Estimated shared audience with similar creators — useful for avoiding overlap (or doubling down) when planning a campaign.

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Ruud 17%

Ricki Yasha Tarr 15%

Chris Geidner 14%

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Adrianna Tan 12%

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Ken Shirriff✓

Make a deal with Ken Shirriff

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Recent posts

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About

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