Ken Shirriff
LightNews LightNews
banner
righto.com
Ken Shirriff
@righto.com
5.7K followers 290 following 350 posts
Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Alto. Ex-Google, Sun, Msft. So-called boffin.
Posts Replies Media Videos
righto.com
Intel's 386 processor (1985) was critical to the success of Intel. With 285,000 transistors, it was too much for Intel's design process and the schedule started slipping. Intel pivoted to "standard cells", an automated technique for chip layout to get back on track. Let's look closer...
A die photo of the 386 processor. It is a square with complicated patterns on top. Under the microscope, the circuits appear in dark purple. Parts of the chip have been marked with boxes: these are standard cell circuits and have a distinctive striped appearance.
November 22, 2025 at 4:56 PM
righto.com
The New York Times recently introduced daily puzzles called Pips. You place the dominoes on the grid so the numbers satisfy the labels.

I solved Pips with cool software called a constraint solver. You give the constraints, e.g. "sum to 8", and it "magically" finds a solution. Let's look closer...
A three-by-three grid of squares with four dominoes below it. Two squares are labeled with "8", indicating that the numbers in that region must sum to eight. Another square is labeled "<5", indicating that the number in that square must be less than 5. The three bottom squares are labeled with an equals sign, indicating that the three numbers must be the same. The upper-right square is missing so there are 8 squares in total, able to hold four dominoes.
October 18, 2025 at 4:20 PM
righto.com
We fixed the vintage IBM printer at the Computer History Museum yesterday. Introduced in 1959, the IBM 1403 line printer provided fast, high-quality output, printing 132 character lines. Unfortunately, one column stopped printing, so we disassembled the printer to fix a bad hammer. Keep reading...
The IBM 1403 line printer is a large unit on a stand, printing on green-bar paper that feeds in at the bottom. The printer is dark gray with a clear plastic cover over the printer and a blue panel at the left with a few control buttons. Behind the printer, three 729 tape drives are visible, each about the size of a refrigerator. The IBM 1401 computer is partially visible at the right, about the size of two refrigerators. It has a control panel with lights, switches, and knobs.
October 2, 2025 at 9:54 PM
righto.com
The iPhone 17 is powered by Apple's A19 SoC (System on a Chip). Chipwise took a die photo of the chip, but it's a bit drab. I spiced it up by applying the over-saturated color gradient that Apple used for die photos of the M1 chip :-)

Link to the original die photo: chipwise.tech/our-portfoli...
A complex die photo with many rectangular and irregular regions. I've applied a color gradient making the photo look slightly rainbow-ish, purple and blue in the top and red and yellow at the bottom. The image has a Chipwise logo on it.
September 23, 2025 at 11:39 PM
righto.com
Celebrated Navajo (Diné) artist Marilou Schultz recently completed a striking weaving. Although this rug may appear abstract, it is a representation of the wiring inside an integrated circuit. It shows the 555 timer, said at one point to be the world's most popular IC. Let's take a closer look...
A Navajo weaving hanging on a wall. The pattern appears abstract: thick white lines in varying directions on a black background. There are some reddish-orange diamonds near the edges, as well as a few thin outlined rectangles. There are three larger squares with a double-H pattern inside. Overall, the pattern looks a bit like an aerial view of roads in a strange ancient city. Thanks to First American Art Magazine for this photo.
September 6, 2025 at 3:25 PM
righto.com
The latest issue of @science.org mentions a magnetic compound Cr2Gr2Te6. The element Gr confused me, but it turned out to be a typo for Ge, germanium. Strangely, I found multiple papers with the same typo in the same context, so I wrote a short blog post about it.
www.righto.com/2025/08/Cr2G...
Text from the journal Science. I've highlighted the formula Cr2Gr2Te6; the rest of the text is not particularly relevant, discussing thin magnetic materials.
August 18, 2025 at 6:47 PM
righto.com
How did Intel's 386 processor connect to the outside world? Tiny wires connect to the bond pads around the edges. Special input/output circuits—visible in zoomed-in blocks—send and receive signals while protecting the chip from dangers that could destroy it. Let's take a look... 1/N
A die photo of the 386 processor. It is a square with complicated patterns on top. Around the edges, 141 square bond pads have tiny gold wires attached to connect the chip to the outside world. In three places, the image zooms in on the bond pads, showing the circuitry associated with the connections.
August 17, 2025 at 2:45 PM
righto.com
Intel's 386 processor was popular in late 1980s microcomputers. From the outside, the 386 chip is a boring ceramic square. But I obtained a 3-dimensional CT X-ray scan from Lumafield, revealing six layers of complex wiring hidden inside the ceramic package. Let's take a closer look... 1/N
An X-ray scan of the 386 chip. It shows a square with a grid of 132 pins. In the middle is a square, the silicon die. Blue wires connect the pins to the chip. Spikes stick out all around the perimeter of the package.
August 9, 2025 at 4:40 PM
righto.com
In 1983, Philips produced the first FM radio receiver on a chip, leading to products such as the FM radio wristwatch. Let's look at the tiny silicon die inside this chip and see how it works. 1/N
A photo of a digital watch with a tuning knob on the front and earbud headphones plugged into the side. Next to it is the wristwatch with the back removed, revealing the batteries inside, along with tiny surface-mount components and a small black integrated circuit.
August 2, 2025 at 3:49 PM
righto.com
We obtained a mysterious box of 1960s electronics. I reverse-engineered it, and with much effort, we got it running. It turns out to be a test unit for testing NASA's Up-Data Link, a system from the Apollo moon landing to control the spacecraft from the ground. Let's take a look inside... 1/n
A gray box of electronics. It has thirteen large orange digits displayed at the top, with lights and switches underneath. These have labels such as Message, UDL Compare, AGC Confirm, and Program Start. A paper tape reader sticks out of the front, with a paper tape threaded through it. The unit is rack-mountable with two handles on the front.
July 21, 2025 at 4:58 PM
righto.com
We're at OpenSauce 2025, showing off Apollo hardware, electromechanical computers, the MOnSter 6502, and other treats. Join me, @tubetime.bsky.social, and Mike at the CuriousMarc booth!
Photo of a booth at OpenSauce. Three tables are covered with vintage electronics of various sorts. Mike is working on the Apollo CDU at the left.
July 19, 2025 at 4:01 PM
righto.com
I'll be at OpenSauce 2025 along with @curiousmarc.bsky.social, @tubetime.bsky.social, and Mike. We plan to show some Apollo hardware, atomic clocks, vintage avionics, and who knows what else, so stop by if you're attending.

opensauce.com
Open Sauce 2025 - Open Sauce
A Celebration Of Makers And Creators. A three-day event in San Francisco Bay Area at San Mateo County Event Center. Attendees will explore...
opensauce.com
July 14, 2025 at 6:50 PM
righto.com
The Globus is a navigational instrument that uses a rotating globe to show the position of the Soyuz spacecraft above the Earth. Inside the Globus, a complicated system of gears and motors positions the globe. @jonbruner.bsky.social at Lumafield created a three-dimensional X-ray scan for us. 1/4
July 11, 2025 at 12:52 AM
righto.com
In the 1960s, this absurdly large camera was used to make masks for integrated circuits. The layers of the integrated circuit were drawn at large scale and then optically shrunk to make the glass masks that were used in manufacturing.
Black and white photo of a giant bellows camera about 8 feet tall. A man is standing in front of the lens which is the size of his torso. Caption: "A copy camera of the type useful in making high-precision photographic masks."
June 25, 2025 at 5:33 PM
righto.com
Last week, the vintage IBM 1401 computer at the Computer History Museum started behaving strangely: it wouldn't halt. More specifically, if you had two HALT instructions in a row, it would halt for the first, but when you continued, it crashed mysteriously. Here's how we fixed it.... 1/N
The IBM 1401 is a vintage computer about the size of two refrigerators. It has dark gray panels with blue and chrome trim. In the upper left, a control panel has numerous lights and buttons. The large line printer is visible in the foreground. A tape drive with two reels of tape is in the background.
June 20, 2025 at 2:57 AM
righto.com
When landing on the Moon, the astronauts watched an instrument called the FDAI that showed the spacecraft's orientation. The ball inside the Flight Director/Attitude Indicator rotated in three axes as the Lunar Module rotated. Let's look inside and see how it works. 1/N
The FDAI is an octagonal instrument with a rotating ball in the center. The ball is half black and half white, with numbers and lines on it to indicate angles. Three yellow needles direct the astronauts with the desired motion. Three arrow scales on the sides show the spacecraft's roll rate in the three axes. An orange flag labeled "OFF" is visible. The cover has been removed from the FDAI so some of the internal components are visible.
June 14, 2025 at 3:37 PM
righto.com
This photo of magnetic core memory popped up, taken by Ansel Adams. I investigated a bit: this memory holds 4000 bits, each stored in a tiny magnetized ferrite ring. It may be from an IBM 705 vacuum-tube business computer. 1/N
A photo with the caption "'Hands weaving magnetic-core memory, IBM, Poughkeepsie, New York', 1956. Photograph by Ansel Adams. This photograph was made on a commercial assignment for IBM." This black-and-white photo shows a core memory plane being assembled. It consists of an 80 by 50 grid of wires in a frame with tiny toroids on the wire intersections. Each wire is attached to metal terminals on the frame. Someone is using tweezers to thread the tiny cores onto the wires. The plane is about 4/5 completed. One hand is below the plane, palm-up, visible through the wires. The other hand (with nail polish) is above the plane, holding tweezers.
May 30, 2025 at 5:38 PM
righto.com
In the Apollo space program, the FDAI (Flight Director Attitude Indicator) showed the orientation of the spacecraft through a ball that rotates on three axes. The yellow needles and black pointers show error and movement rate. This FDAI was later modified for use in a Space Shuttle simulator.
An indicator with a rotating ball in the middle. The top half of the ball is black and the bottom is white. The ball has various lines and angle markings on it. Three yellow needles project across the ball to indicate the error in each axis. Three scales with needle pointers show the rotation rate in the three axes. The scales are illuminated. Two power wires run to clips attached to the interior of the FDAI, which has its cover removed.
May 21, 2025 at 4:21 PM
righto.com
How thin is spider silk compared to the wiring on a chip? Here's a close-up of a spiderweb strand diagonally across an Intel 386 processor. The spiderweb is 4 µm thick, just a bit thinner than this 1985 chip's 5 µm metal wiring. Wiring in modern chips is 100 times thinner.
A close-up of the die of the Intel 386 processor showing the metal layers. A strand of a spider web runs diagonally across the image. The processor image consists of yellowish metal wiring running horizontally and vertically, with more complex patterns underneath. Black circles indicate connections between the two metal layers. The spider web is about the same thickness as the metal wiring. The silicon circuitry underneath is not visible, but its feature size is 1.5 µm, considerably thinner than the spider web.
May 17, 2025 at 7:01 PM
righto.com
Tape drive repair at @computerhistory.bsky.social. I helped @tubetime.bsky.social figure out why the tape drives wouldn't backspace. The problem turned out to be a bad germanium transistor on an inverter card. 1/5
May 16, 2025 at 9:39 PM
righto.com
Anyone use Intel's 386 processor from 1985, the first 32-bit x86? To improve performance, it preloaded instructions into a 16-byte prefetch queue (highlighted in red). Why does such a small queue take up so much of the chip? Let's look under the microscope at its complicated circuitry... 1/N
A die photo of the Intel 386 processor. It looks a bit like an aerial photo of a weirdly-zoned city, with rectangular blocks of various textures in a complicated arrangement. The functional units of the chip are labeled. In particular, the Prefetch Unit is near the upper left corner. A large red rectangle is labeled Prefetch Queue.
May 10, 2025 at 4:23 PM
righto.com
Intel's 386 processor (1985) moved the x86 architecture to 32 bits, but it needed to be backward compatible with earlier 16 and 8-bit processors. As a result, it needed complicated circuitry for its internal registers: six different circuits for 30 registers. Let's look at the silicon circuits. 1/N
A die photo of the Intel 386 processor under the microscope. The die has complex patterns that make up the different parts of the chip. The various blocks are roughly rectangular with different textures. The main functional blocks are labeled, including the paging unit, bus interface unit, prefetch unit, segment unit, instruction decode unit, protection test unit, data unit, and control unit. The register file, the subject of this thread, is in the lower left corner, highlighted by a red rectangle. This die photo image has a purple tint.
May 1, 2025 at 5:40 PM
righto.com
If you were following my recent repair of a vintage Commodore PET home computer, you may enjoy this video from @curiousmarc.bsky.social:
Hard to repair Commodore PET
YouTube video by CuriousMarc
youtu.be
April 24, 2025 at 3:35 PM
righto.com
The Commodore PET, along with the Apple II and the Radio Shack TRS-80, formed the "1977 Trinity" that made home computers popular. The PET was very quirky, combining a tiny keyboard, a cassette drive for storage, and a monitor in a trapezoidal case. I got one, but it didn't work. Let's fix it... 1/N
A photo of a Commodore PET. The screen is full of garbage characters. The computer is a white metal case with a keyboard made of small square keys in a grid. The keys are mostly white but some are red or blue. The keys have strange graphics symbols on them in addition to the normal QWERTY keys. To the left of the keyboard, a black cassette deck is mounted in the computer. The monitor is in a trapezoidal metal case that is mounted on top of the main part of the case. The computer has a large logo on the front: Commodore PET 2001 series personal computer.
April 13, 2025 at 4:15 PM
righto.com
If any of my followers want to read about the Pentium in German, one of my articles has been translated:
www.heise.de/hintergrund/...
Zahlen, bitte! Verrückt: Für ×3 brauchte der Pentium einen eigenen Schaltkreis
Der Intel Pentium hat einen separaten Abschnitt nur für die Multiplikation mit 3. Dieser verfügt über mehr Transistoren, als ein Z80 insgesamt hatte. (Teil 1)
www.heise.de
April 2, 2025 at 3:44 AM