Ken Shirriff's blog
npub1nemc75lrjgraut8p5pkd6czsj3rq9s8w3k5vj23x8a27p3yghahq3r7e80@drss.io
Computer history, restoring vintage computers, IC reverse engineering, and whatever
Examining circuit boards from the Space Shuttle's I/O Processor
28 Jun 2026
The Space Shuttle's five[1](#fn:computers) general-purpose computers played a critical role in each flight: controlling the engines, monitoring thousands of sensors, displaying data to the
The adder at the heart of Intel's 8087 floating-point chip
13 Jun 2026
In 1980, Intel released the Intel 8087 floating-point coprocessor, a chip that could make math up to 100 times faster. As well as arithmetic and square roots, the 8087 computed transcendental
Powering up a module from the IBM 604: an electronic calculator from 1948
7 Jun 2026
1948 was an interesting time for computing. For decades, businesses had used punch card equipment that added and sorted electromechanically. Now these electromechanical relays and counting wheels
Microcode inside the Intel 8087 floating-point chip: register exchange
30 May 2026
In 1980, Intel introduced the 8087 floating-point chip, a co-processor that made floating-point operations up to 100 times faster. This chip was highly influential, and today most processors use the
Reverse engineering circuitry in a Spacelab computer from 1980
23 May 2026
Spacelab was a reusable laboratory that could be carried in the cargo bay of the Space Shuttle, providing lab space for astronauts and experiments. Spacelab was controlled by a French-built
The electromechanical angle computer inside the B-52 bomber's star tracker
18 Apr 2026
Before GPS, how did aircraft navigate? One important technique was celestial navigation: navigating from the positions of the stars, planets, or the sun. While celestial navigation is accurate,
The rise and fall of IBM's 4 Pi aerospace computers: an illustrated history
29 Mar 2026
The morning of April 12, 1981, 20 years to the day after Yuri Gagarin became the first person in space, the Space Shuttle thundered into the Florida sky. Commander Young and Pilot Crippen were at the
Instruction decoding in the Intel 8087 floating-point chip
14 Feb 2026
In the 1980s, if you wanted your IBM PC to run faster, you could buy the Intel 8087 floating-point coprocessor chip. With this chip, CAD software, spreadsheets, flight simulators, and other programs
Notes on the Intel 8086 processor's arithmetic-logic unit
23 Jan 2026
In 1978, Intel introduced the 8086 processor, a revolutionary chip that led to the modern x86 architecture. Unlike modern 64-bit processors, however, the 8086 is a 16-bit chip. Its arithmetic/logic
Conditions in the Intel 8087 floating-point chip's microcode
30 Dec 2025
In the 1980s, if you wanted your computer to do floating-point calculations faster, you could buy the Intel 8087 floating-point coprocessor chip. Plugging it into your IBM PC would make operations up
The stack circuitry of the Intel 8087 floating point chip, reverse-engineered
9 Dec 2025
Early microprocessors were very slow when operating with floating-point numbers. But in 1980, Intel introduced the 8087 floating-point coprocessor, performing floating-point operations up to 100
Unusual circuits in the Intel 386's standard cell logic
22 Nov 2025
I've been studying the standard cell circuitry in the Intel 386 processor recently. The 386, introduced in 1985, was Intel's most complex processor at the time, containing 285,000 transistors.
Solving the NYTimes Pips puzzle with a constraint solver
18 Oct 2025
The New York Times recently introduced a new daily puzzle called [Pips](https://www.nytimes.com/games/pips). You place a set of dominoes on a grid, satisfying various conditions. For instance, in the
A Navajo weaving of an integrated circuit: the 555 timer
6 Sep 2025
The noted Diné (Navajo) weaver Marilou Schultz recently completed an intricate weaving composed of thick white lines on a black background, punctuated with reddish-orange diamonds. Although this
Why do people keep writing about the imaginary compound Cr2Gr2Te6?
18 Aug 2025
I was reading the latest issue of the journal *Science*, and a paper mentioned the compound Cr2Gr2Te6. For a moment, I thought my knowledge of the periodic table was slipping, since I couldn't
Here be dragons: Preventing static damage, latchup, and metastability in the 386
17 Aug 2025
I've been reverse-engineering the Intel 386 processor (from 1985), and I've come across some interesting circuits for the chip's input/output (I/O) pins. Since these pins communicate with the outside
A CT scanner reveals surprises inside the 386 processor's ceramic package
9 Aug 2025
Intel released the 386 processor in 1985, the first 32-bit chip in the x86 line. This chip was packaged in a ceramic square with 132 gold-plated pins protruding from the underside, fitting into a
How to reverse engineer an analog chip: the TDA7000 FM radio receiver
2 Aug 2025
Have you ever wanted to reverse engineer an analog chip from a die photo? Wanted to understand what's inside the "black box" of an integrated circuit? In this article, I explain my reverse
Reverse engineering the mysterious Up-Data Link Test Set from Apollo
21 Jul 2025
Back in 2021, a collector friend of ours was visiting a dusty warehouse in search of Apollo-era communications equipment. A box with NASA-style lights caught his eye—the "AGC Confirm" light
Inside the Apollo "8-Ball" FDAI (Flight Director / Attitude Indicator)
14 Jun 2025
During the Apollo flights to the Moon, the astronauts observed the spacecraft's orientation on a special instrument called the FDAI (Flight Director / Attitude Indicator). This instrument showed the
Reverse engineering the 386 processor's prefetch queue circuitry
10 May 2025
In 1985, Intel introduced the groundbreaking 386 processor, the first 32-bit processor in the x86 architecture. To improve performance, the 386 has a 16-byte instruction prefetch queue. The purpose
The absurdly complicated circuitry for the 386 processor's registers
1 May 2025
The groundbreaking Intel 386 processor (1985) was the first 32-bit processor in the x86 architecture. Like most processors, the 386 contains numerous registers; registers are a key part of a
A tricky Commodore PET repair: tracking down 6 1/2 bad chips
13 Apr 2025
mult3 In 1977, Commodore released the PET computer, a quirky home computer that combined the processor, a tiny keyboard, a cassette drive for storage, and a trapezoidal screen in a metal unit. The
Notes on the Pentium's microcode circuitry
31 Mar 2025
Most people think of machine instructions as the fundamental steps that a computer performs. However, many processors have another layer of software underneath: microcode. With microcode, instead of
A USB interface to the "Mother of All Demos" keyset
23 Mar 2025
In the early 1960s, Douglas Engelbart started investigating how computers could augment human intelligence: "If, in your office, you as an intellectual worker were supplied with a computer display