Ken Shirriff

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

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kenshirriff_at_oldbytes.space@mostr.pub

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Last Notes

2024-09-28 15:30:36

The F-4 fighter plane used an attitude indicator to show the plane's orientation. The ball in this indicator rotates in three axes. How does that work? We took the indicator apart to find out.
Spoiler: the ball is two hollow hemispheres, rotating while the "equator" stays stationary. Keep reading for details...
1/N
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/113/215/882/989/099/428/original/bec431b9eb464fa6.mp4

2024-09-02 16:28:09

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Why is the die photo distorted at the edges? Because I took the photo through the chip's round quartz window. In the olden days before flash, you could store code in an EPROM, memory that could be erased by exposing it to strong ultraviolet light. The quartz window lets the light in. 2/7
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/113/068/895/785/637/211/original/148bff6468fccae1.jpeg

2024-09-01 16:20:51

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For more information on the Pentium weaving, see my latest post: https://www.righto.com/2024/08/pentium-navajo-fairchild-shiprock.html 6/6

2024-09-01 16:15:32

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The weaving of a Pentium is so accurate that I could label the functional blocks of the processor. Amusingly, the gallery hung the weaving backward. The wrong side is facing outward, so the chip is mirrored. I had to flip the image to make this diagram. 2/6
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/113/063/184/554/912/516/original/e83be7f2b95085d1.jpg

2024-09-01 16:14:25

I recently saw an amazing Navajo rug at the National Gallery of Art. It looks abstract at first, but it is a detailed representation of the Intel Pentium processor. Called "Replica of a Chip", it was created in 1994 by Marilou Schultz, a Navajo/Diné weaver and math teacher. Intel commissioned the weaving as a gift to the American Indian Science & Engineering Society. 1/6
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/113/063/175/736/324/400/original/52f18cfa73d6a169.jpeg

2024-09-01 16:14:25

2024-08-19 18:21:40

The Minuteman III missile (1970) is America's land-based nuclear deterrent, with 400 missiles ready to launch. The missile used a complex guidance system with over 17,000 electronic and mechanical parts that cost $4.5 million in current dollars. Let's take a look at the guidance system and computer. 1/N
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/990/062/420/406/552/original/4fd91a86b7e55586.jpeg

2024-08-03 14:52:40

The Space Shuttle had a 59-pound printer on board, known as the Interim Teleprinter. Putting this heavy printer in orbit cost $1.5 million per flight, but it was a key piece of flight hardware,
providing the astronauts with mission plans, weather reports, and other documents from Mission Control. Let's take a look inside... 1/12
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/898/649/819/144/816/original/7b31f9a9160285d6.jpeg

2024-07-16 18:41:34

This pretty chip from 1981 helped connect an IBM mainframe to data-entry terminals. 1/14
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/797/633/313/440/029/original/2beb6f534665f07d.jpg

2024-07-07 17:40:39

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Standard cells use a library of standardized blocks for gates and other circuits. Software builds your circuit by snapping the blocks into rows and laying out the wiring between the circuits. Quick and error-free, but not as dense and efficient as manual circuit design. 3/21
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/746/433/017/449/547/original/f2046fd097795a0b.jpg

2024-07-07 17:40:37

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The fingernail-sized Pentium chip under a microscope. Some parts, like the cache and datapath were highly optimized by hand. Less critical areas, outlined in red, were designed by software using standard cells. The rows of cells are visible as gray columns. 2/21
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/746/432/865/083/163/original/f1e49661e3da4c75.jpg

2024-07-07 17:40:34

Intel's Pentium processor (1993) was a big jump in processor performance, starting a brand that lasted until 2023. But what's inside the Pentium chip? How did Intel organize its 3.3 million transistors? Let's take a look inside and see the chip's "standard cells". 1/21
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/746/432/625/903/771/original/1c80fe67361102bb.jpeg

2024-06-23 16:01:42

To use the Montreal subway, you tap a paper ticket against the turnstile and it opens. But how does it work? And how can the ticket be so cheap that it's disposable? I opened up the tiny NFC chip inside to find out more... 1/15
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/666/771/557/655/427/original/d1ff1367c9e0a2b0.jpg

2024-05-29 14:19:46

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The mechanical construction of the computer is clever, allowing the densely packed boards to unfold like a book. Each "page" consists of two boards mounted back-to-back. The metal frame provides conductive cooling as well as support. 2/17
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/524/813/011/938/671/original/6be5cb4a71fc918d.jpg

2024-05-29 14:19:44

I received a mysterious aerospace computer from the early 1970s, probably for navigation. It is crammed full of flat-pack integrated circuits surrounding a core memory module. Let's take a look inside... 1/17
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/524/812/828/746/391/original/2453ca743d6ad858.jpg

2024-04-28 15:37:42

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The Datamaster, also known as the IBM System/23, was released in July 1981, just a month before the IBM PC. The 16-bit PC overshadowed the 8-bit Datamaster as it was both more powerful and cheaper. But the Datamaster is interesting since it is the IBM PC's parent. 2/8
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/349/587/802/831/126/original/972feb91b01afa0f.jpg

2024-04-25 17:34:39

Punch cards used to be a key part of computing. The IBM 1402 Card Reader/Punch (1959) could read or punch hundreds of cards a minute. But the punch at https://twitter.com/ComputerHistory stopped punching the first 16 columns. An explanation of the punch unit and how we fixed it... 1/9
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/333/060/744/911/012/original/35407fd4f09d727d.jpg

2024-03-30 17:30:12

Here's an unusual chip, a 7400-series decoder implemented with a gate array. It has over 1500 transistors in orderly rows, but most of them are entirely unused. Why build a chip in such an inefficient way? Let's take a closer look... 1/13
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/185/823/146/432/846/original/ce2ab3c373eaafb6.jpg
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/185/823/196/925/791/original/9427d909cd11ee00.jpg

2024-03-23 16:42:59

Intel introduced the 8088 processor in 1979. IBM selected the 8088 for the IBM PC, a moment in computer history that ensured the dominance of Intel and x86.
To improve performance, the 8088 prefetched instructions. Let's look at the prefetch circuitry inside the 8088... 1/12
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/146/001/256/783/878/original/bebd4c5c3c7af3f3.jpg

2024-03-19 20:39:44

The Space Shuttle had a large teleprinter onboard so the astronauts could receive text documents. We want to get it working, but first some reverse engineering... 1/13
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/112/124/283/027/479/605/original/16b1a0363f7921c3.jpg

2024-02-11 17:47:04

The Bendix CADC is an analog computer used by fighter planes in the 1950s. It computed airspeed, Mach number, and other important parameters. I reverse-engineered how it performed these calculations with tiny gears, differentials, and cams. 1/12
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/111/914/098/615/788/149/original/65b1f3dd6ea5643e.jpg

2024-02-03 18:01:29

The Intel 386 processor (1985) was a key step in the evolution of x86, moving to 32 bits as well as a CMOS implementation. A less visible design change is its use of standard cell logic (marked in red), building many circuits from standardized building blocks. 1/17
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/111/868/856/784/698/231/original/9097b69906b05b4c.png

2023-08-12 16:27:44

The ancestor of the 8086 processor is the Datapoint 2200, a desktop minicomputer used as an intelligent terminal. Made before the microprocessor, the Datapoint built a processor from a board of chips. The Intel 8008 cloned the Datapoint, first step to the x86 architecture. 🧵
https://assets.oldbytes.space/assets.oldbytes.space/media_attachments/files/110/877/583/827/805/527/original/f0beefffd49d60ba.jpg