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...

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 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...

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...

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...

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

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

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

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

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!

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

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

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.

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

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

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

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.

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.

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

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

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

If you were following my recent repair of a vintage Commodore PET home computer, you may enjoy this video from @curiousmarc.bsky.social:

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

If any of my followers want to read about the Pentium in German, one of my articles has been translated: www.heise.de/hintergrund/...

The Pentium processor, like many others, implements its instructions in microcode. Each step of an instruction is described by a micro-instruction, stored in the chip in the microcode ROM. This die photo shows the parts of the Pentium. Let's take a quick look at the microcode ROM...1/N

Just discovered that Jonah Goldberg, journalist and magazine editor, is a different person from Jeffrey Goldberg, journalist and magazine editor. Things make much more sense now!

I read an interesting paper on the history of the QWERTY keyboard. The keyboard evolved from an 1859 keyboard with half the alphabet in order and the second half backward. You can still see this ordering on the bottom rows of the modern keyboard, although many keys have moved over the years.

i've built a reproduction chord keyboard (keyset)! this device was invented along with the computer mouse by Douglas Engelbart's team at SRI back in the 1960s. unlike the mouse, it never took off. files are here: github.com/schlae/engel...

In 1968, Douglas Engelbart revolutionized computing by showing the mouse, hypertext, and collaborative computing in "The Mother of All Demos". Most of his ideas are now part of everyday computing, but one device—the keyset—failed to catch on. Let's look at Engelbart's demo and the keyset. 1/N

Happy Pi Day from a vintage IBM 1401 computer at the Computer History Museum (@computerhistory.bsky.social). This image is composed of the digits of π, printed on the 1403 line printer.

The Pentium Processor’s Innovative (and Complicated) Method of Multiplying by Three, Fast

Obscure electronics history: In this recent protest photo, why is the truck logo so similar to Fry's Electronics (which closed in 2021)? Answer: Fry's Food was founded in 1954 by Donald Fry and sold in 1972. His nephews founded Fry's Electronics with the proceeds. Thus, similar logos.

Intel's Pentium processor (1993). Looking inside the chip , I found a large, complicated circuit just to multiply by 3 (lower right). Why? The Pentium uses a fast technique to multiply 64-bit number and it turns out that 3 is a special case. Let's take a closer look at multiplication... 1/N

The F-4 fighter plane used a three-axis attitude indicator to show the plane's orientation. (Like an artificial horizon with a third axis.) @curiousmarc.bsky.social, @tubetime.bsky.social, and I restored a damaged indicator. The video includes burning slip rings: www.youtube.com/watch?v=snP_...

What is the origin of the word "mainframe"? Digging through archives, I traced it back to 1953. The IBM 701 computer was built from "frames": power frames, a storage frame, a drum frame, and the main frame. This 1953 drawing from the Installation Manual shows the dimensions of the "main frame". 1/n

We examined a Xerox Alto disk pack from the 1980s and found this mysterious diagram. It turns out to be from "The Limits to Growth", a 1972 book on world collapse. There's also a connection with the invention of core memory and the Whirlwind computer. Let's take a look... 1/6

Intel's Pentium processor (1993) was a complex chip for its time, with 3 layers of metal wiring over the silicon. I removed the layers, one at a time, so we can take a look at each layer... 1/n

The revolutionary Xerox Alto computer (1973) started GUI computing, Ethernet, the optical mouse, laser printing, and visual word processing. We came across a password-protected Alto disk so I cracked the password. @tubetime.bsky.social looks at the contents: bsky.app/profile/tube...

Adding on a computer is trickier than you'd expect. The Pentium processor (1993) used a variety of circuits for addition. I reverse-engineered an adder in the floating point unit and found that it is a "Kogge-Stone carry-lookahead adder", using some tricks to make it faster. Let's look inside. 1/n

The bsky website has started putting a circle near the bottom of the page that partially obstructs the text. Is this new? Is there any way to make it go away? It is very distracting and annoying.

Intel's Pentium processor (1993) can compute sines, logarithms, and other special functions. To do this, it has a ROM with 304 floating-point constants. I reverse-engineered this ROM and extracted the constants. You can see pi in the ROM, binary 11.001001..., encoded in the transistor pattern. 1/n

Lemon pig for the New Year!

In 1994, a math professor discovered that Intel's Pentium chip sometimes gave the wrong answer when dividing. Fixing this "FDIV" bug cost Intel $475 million. I analyzed the Pentium chip and found the bug. 1/N

"Now! A computer makes Christmas gift shopping easier." In 1962, some stores had an IBM 1401 computer that could make the perfect gift selections for you. You specify the recipent's age, interests, gender, and a price range, and the computer generates the perfect gift selections.

Merry punch-card Christmas from the vintage IBM 1401 computer!

A vintage Intel video on the 386 processor, feat. Pat Gelsinger and Gene Hill, just dropped on YouTube. youtu.be/LQcLhBZY12g Thanks to @computerhistory.bsky.social for digitizing this.

If the surgery is done with a what now? Horoscope? Leprosy rope? This patient education video from Kaiser needs better subtitles.

Intel launched the Pentium processor in 1993. Unfortunately, dividing sometimes gave a slightly wrong answer, the famous FDIV bug. Replacing the faulty chips cost Intel $475 million. I reverse-engineered the circuitry and can explain the bug. 1/9

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. 1/n

I was studying the Pentium processor's die and I noticed strange connections that I didn't understand. These turned out to be "antenna diodes", special diodes that protect the chip from damage during manufacturing. Let's take a look... 1/6