Ken Shirriff
LightNews LightNews
banner
righto.com
Ken Shirriff
@righto.com
5.7K followers 290 following 340 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
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.
A Pips problem with the solution. It has numbers in the cells, corresponding to dominoes. A much larger Pips puzzle, a 6 by 6 grid in an octagonal shape. It has 12 dominoes and many constraints. The image shows the solution.
October 18, 2025 at 4:20 PM
righto.com
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.
The same 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. Code: constraint pips[1,1] + pips[2,1] == 8; constraint pips[2,3] < 5; constraint all_equal([pips[3,1], pips[3,2], pips[3,3]]); Code: grid = [| 1,1,0| 1,1,1| 1,1,1|]; Code: spots = [|5,1| 1,4| 4,2| 1,3|];
October 18, 2025 at 4:20 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
The hammers looked okay, but @tubetime.bsky.social found that hammer #83 was sticky. He cleaned it and then the printer worked, just in time for the demo. (Stop by the museum on Wednesdays or Saturdays to see the system in operation.) Photo shows a hammer from an earlier repair.
A hammer assemblly with the coil attached. It is an irregularly-shaped metal unit that is kind of grungy. It looks vaguely like an elephant with a long, straight trunk forming the part that hits the paper.
October 2, 2025 at 9:54 PM
righto.com
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.
The back side of the printer after removing the cover, paper guides, and cooling air hose. The hammer unit is a big gray unit in the middle. On either side, metal guide rails have been attached to the printer and stick out horizontally. The hammer unit has been slid out along the guide rails and tilted up. With the cover removed, you can see 33 electromagnetic coils in a row with a jumble of wiring behind. Each coil has a hammer, a gray rectangle of metal. At the bottom of the photo is a row of 132 small rectangles. These are the ends of the hammer that hit the paper to print characters.
October 2, 2025 at 9:54 PM
righto.com
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
The print chain unit, about 14 inches wide and maybe an inch high. A chain is visible at the front with a sequence of raised charcters in reverse. An output page from the printer, displaying successive powers of two. One column stops printing partway down the page, with the failures circled in red ink. "Column 82" is written on the page, but it turns out that column 83 is the bad column.
October 2, 2025 at 9:54 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
Marilou Schultz first made a chip rug in 1994, when Intel commissioned a rug based on the Pentium as a gift to AISES (American Indian Science & Engineering Society). The Pentium weaving used natural dyes, while the 555 weaving uses aniline dyes and some metallic threads for more intense colors.
A rug representing the Intel Pentium processor. The style of this rug is very different from the previous one. It is a Navajo rug with a complex pattern with muted reds, pinks and blues. The pattern consists of various vertical and horizontal rectangles with stripes. Around the border are small alternating black and colored rectangles. The weaving is mounted in a wooden frame and hanging on the museum wall.
September 6, 2025 at 3:25 PM
righto.com
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.
An image of the rug next to a photograph of the 555 chip's die. Both are white patterns on a black background. They match closely, but there are a few changes. The wiring at the top has been simplified. The part number at the bottom has been removed.
September 6, 2025 at 3:25 PM
righto.com
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.
An integrated circuit in a metal can, sitting on top of a penny. I cut the top off the metal can, revealing the silicon die inside. The silicon die itself is a bit bigger than Lincoln's nose. Eight tiny bond wires connect the silicon die to the eight pins around the periphery of the metal can.
September 6, 2025 at 3:25 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
The 386 uses a complicated circuit, based on a memory chip's "sense amplifier" to reduce metastability. The sense amplifier speeds up the decision between 0 and 1. This circuit is relatively large, so only a few pins need it, inputs with unpredictable timings.
Another close-up die photo. This one shows more circuitry than the previous ones. It shows two standard latch circuits, along with two special sense-amplifier latch circuits that reduce metastability. The sense-amp latch circuits are larger than the regular latches. The diagram also shows protection diodes and guard rings. At the bottom, the large square bond pad is where the bond wire is attached. A schematic with a bunch of transistors. At the top are two latches, active in the first clock phase. At the bottom is the sense amplifier, active in the second clock phase. The sense amplifier has cross-coupled transistors, similar to cross-coupled inverters. But it also has similarities with a differential amplifier.
August 17, 2025 at 2:45 PM
righto.com
The third danger facing a chip is "metastability". If a signal arrives at just the wrong time, the circuit can get stuck between 0 and 1 for a while before deciding on 0 or 1. This causes wrong results. It's like a ball wobbling on top of a hill, eventually rolling down one side or the other.
An image showing metastability. This is a brownish oscilloscope trace showing an input signal that drops from high to the middle. Then, numerous dots show the signal becoming either high or low after spending an unpredictable time between high and low. An image of a ball balancing on top of a hill. From this metastable state, it can roll down either side of the hill to a stable state.
August 17, 2025 at 2:45 PM
righto.com
The second danger facing a chip is "latchup": if the voltage on a pin is out of range, unwanted "parasitic" transistors can turn on, shorting power to ground and burning out the chip. Special "guard rings" around the I/O transistors block unwanted currents to prevent latchup.
A close-up of the die, showing an I/O circuit similar to the previous one. This photo highlights the two nested rectangular "guard" rings around the transistors. One ring is connected to ground and the other is connected to +5. These rings soak up current that escapes the transistors.
August 17, 2025 at 2:45 PM
righto.com
Static electricity is a danger to chips. The tiny transistors inside a chip use thin layers of glass-like silicon dioxide, just 250 nm thick, thinner than a virus. Static electricity can easily blow a hole through this layer, destroying the chip. Special diodes redirect static electricity safely.
A close-up of the protection circuitry for one of the 386's pins. In this die photo, I removed the metal layers to reveal the silicon underneath. It consists of tan rectangular and grid-like patterns from the transistors. A large square region at the right is labeled "pad". Components are labeled on the die image: resistor, diodes, capacitor, and inverters.
August 17, 2025 at 2:45 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
I found an integrated circuit with tiny Chinese-style tally marks in the upper right corner. The chip was built by Integrated Device Technology (IDT) in 1991; IDT was an American company, so I don't know why the tally marks are Chinese.
Die photo of an integrated circuit. The circuitry is in nine uniform rows of rectangles since it is a gate array. Bond wires are connected around the perimeter of the chip. A close-up of the die with various letters and symbols. The initials JL, SH, and MM are visible, along with two plus signs. The Chinese character 正 appears three times, once with all five lines, once with four lines, and once with just two lines.
August 9, 2025 at 8:19 PM
righto.com
Here are the remaining four layers inside the package: one signal layer and three power layers. There are four power layers altogether so the chip's I/O circuitry and logic circuitry can be powered separately. That way, current surges from I/O don't affect the CPU.
Another scan of a power layer. It shows a bluish-green square with a grid of small holes. This one has many red dots. Another power layer scan. This one shows many blue-yellow bond wires in the center, connecting the package to the die. Another scan of a signal layer, showing blue-green "tentacles" reaching out from the center square. Another scan showing a bluish-green square with a grid of small holes. This one has just a few red dots. This layer is farthest from the pins, so most of the pins (red dots) don't reach this far.
August 9, 2025 at 4:40 PM
righto.com
One of the six power layers inside the Intel 386 processor's packaging. It's almost a solid conductive plane; the grid of holes joins the ceramic above and below. Most of the pins are connected to lower layers, so only a few pins (red dots) reach this layer.
This scan shows a bluish-green square with a grid of small holes, a bit like a piece of fabric full of holes for ventilation. It has a square cut out of the middle with a blue square in the hole. Several dozen red dots are scattered over the image, about half of them are surrounded by black rings.
August 9, 2025 at 4:40 PM
righto.com
The CT scan of a signal layer inside the 386's package. The wide abstract-looking regions connect the pins (red dots) to the chip in the middle. Unexpectedly, I spotted thin wires running to the edges of the chip. These are used during manufacturing to electroplate the pins with gold.
A colorful CT scan. There is a blue square in the center (the silicon die). Multicolored blobs reach out from the die, a bit like a sunburst in blues, greens, and yellows, or maybe like a tentacled sea creature. A grid of red dots over the image corresponds to the pins. Thin reddish-orange lines reach out to the edges of the ceramic package. The ceramic package itself is visible as a blue square background. The four corners of the package are clipped, three very slightly clipped and one clipped a bit more.
August 9, 2025 at 4:40 PM
righto.com
The silicon die of the 386 processor is mounted in the middle of the ceramic package. Tiny bond wires connect the die to two tiers of contacts that surround it. Intricate but hidden wiring inside the ceramic connects these contacts to the 132 gold-plated pins. 2/N
The 386 processor is a ceramic square with 132 pins. The metal lid in the center has been removed, showing the silicon die underneath. Gold contacts surround the die. A close-up of the 386 package. The gray silicon die is connected to the metal contacts of the package through tiny gold bond wires. These contacts are arranged in two tiers around the die. At the top of the photo, four gold pins are visible.
August 9, 2025 at 4:40 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
A diagram with more details. It's a 7-stage shift register, but only the first four stages are bonded to pins, so a 4-stage shift register, unless there's feedback. I think data is bottom left and clk is bottom right. I'm suspicious of the first flip-flop output; I don't see the wire I expected.
A die photo with 11 pads labeled and complex metal wiring, colored by hand. There are 7 flip-flops connected as a shift register.
August 8, 2025 at 2:51 AM