Ken Shirriff
Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Alto. Ex-Google, Sun, Msft. So-called boffin.
- The arithmetic/logic unit (ALU) in the Intel 8086 processor (1978) is more complicated than you might expect, performing 28 different operations from addition and logical AND to shifts and BCD adjustment. A special control circuit reconfigures the ALU for each operation. Let's look closer...
- The 8086 processor uses microcode to specify each step of an instruction. The circuitry below decodes the microcode and sends control signals to the ALU so it performs the desired arithmetic or logic operation. In this die photo, you can see the individual transistors in the circuitry.
- For more, see my latest blog post: www.righto.com/2026/01/note...
- Intel announced the 8087 floating-point chip in 1980. Now I have a blog post that explains a small part of the microcode in this chip. www.righto.com/2025/12/8087...
- In 1980, Intel announced the 8087 Math Coprocessor, a chip that made floating-point 100 times faster. I opened up the chip, took photos of the silicon structures, and analyzed its circuitry. It's a very complex chip for its time. Let's take a look inside...
- Unlike most processors, the 8087 organizes its registers into a "stack", pushing numbers onto the top of the stack and popping them off. Here's a close-up of the eight registers, organized in a grid of cells. Each register holds an 80-bit number, so the registers are very tall.
- Each bit is stored in a "static RAM" cell, consisting of two inverters in a loop. This circuit has two stable states, holding a 0 or a 1. The implementation is complicated: silicon with polysilicon lines on top to make transistors. Horizontal metal wires connect everything.
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View full threadFor more on the stack circuitry in the 8087, see my blog post: www.righto.com/2025/12/8087...
- 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...
- The previous photo shows the 386 processor under a microscope. I've highlighted the regions that use standard cells and the layout was automated. Simple logic blocks (the "standard cells") are arranged in rows, with wiring between the rows. This creates a distinctive striped pattern.
- It's much easier to build circuits with standard cells. Instead of manually arranging each transistor, you feed a description of the logic into a computer. It places the cells into rows, and then routes the wires to connect the cells. In 1985, this took many hours on an IBM mainframe computer.
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View full threadMy latest blog post describes the wayward transistor and two other curiosities in the 386 processor's standard cell logic, so read it for details. www.righto.com/2025/11/unus...
- 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...
- I used a constraint solver called MiniZinc. I wrote constraints for the problem: the conditions on the grid, the shape of the grid, and the values of the dominoes. A few more constraints defined how the problem works. I didn't need to write algorithms because MiniZinc solves automatically.
- MiniZinc gave me a solution to the Pips puzzle in 100 milliseconds. Admittedly, this puzzle is rated "easy", but MiniZinc quickly solves hard puzzles too. Internally, MiniZinc uses complicated algorithms such as backjumping and constraint propagation, but I don't need to worry about that.
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View full threadMiniZinc solver page: www.minizinc.org Link to Pips: www.nytimes.com/games/pips The article on HN that inspired me to investigate constraint solvers: buttondown.com/hillelwayne/...
- 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 line printer uses a chain with raised characters that spins at high speed. It has 132 hammers, one for each column. When the right character on the chain is in front of a hammer, the hammer fires, printing that character. But if a hammer fails, that column doesn't print, as you can see. 2/N
- We took the hammer unit out of the printer. Fortunately, IBM designed the printer for (relatively) easy maintenance. Inside the printer are two rails that can be attached to the back. The hammer unit slides out and tilts for access. You can see some hammers and coils; more are underneath.
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View full threadIf you want to know more about the IBM 1403 printer, I wrote about how we played music on it: www.righto.com/2019/09/risk... I also made an animation to explain the extraordinarily complicated timing between the hammers and the chain to print characters: static.righto.com/ibm1401/prin...
- 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...
- Here's a photo of the silicon die of the 555 chip—it's packaged in a metal can, rather than usual plastic rectangle, with 8 pins in a circle. If you zoom way in, you can see the pattern on the silicon matches the rug, in particular, the three large squares with a 王 pattern.
- Marilou Schultz based the rug on a photo by Antoine Bercovici (Siliconinsider). He used a special dark field microscope that produces a black background, highlighting the metal wiring on top of the silicon. The rug (left) mostly matches the photo (right), but there are some artistic changes.
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View full threadMarilou Schultz's rug is on display at SITE Santa Fe's current exhibition: "Once Within a Time"; let me know if you see it! Photo credit: rug photo from First American Art Magazine (@firstamart.bsky.social).
- 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...
