Ken Shirriff
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Ken Shirriff
@righto.com
5.8K followers 290 following 360 posts
Computer history. Reverse-engineering old chips. Restored Apollo Guidance Computer, Alto. Ex-Google, Sun, Msft. So-called boffin.
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Intel was hesitant to produce the 8087 chip, considering it complex, risky, and with an unknown market. Intel's Israel site took on the project; the die is marked "i/IL". The chip was a highly profitable success. Now, almost all computers use floating-point systems based on the 8087.
A close-up of the 8087 die. There are white horizontal and vertical lines of various widths, the chip's metal wiring. Text in metal is also visible: "8087", "i/IL", and a maskwork/copyright marking: "(m) (c) intel 1980".
December 9, 2025 at 6:38 PM
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This diagram, based on the 8087 patent, shows the implementation of the stack. You saw the registers (yellow) earlier. This photo shows the three-bit circuitry that controls the stack (purple, green, and blue). The schematic shows one bit in detail.
A block diagram from the patent. It shows the top-of-stack pointer (TOS) with controls to increment and decrement when pushing or popping values. A subtractor circuit computes offsets into the stack. A multiplexer selects either the top-of-stack or the offset value. A decoder selects one entry in the stack based on this value. The value in the stack is split across the fraction bus, exponent bus, and tag bus. The stack control circuitry on the die. It consists of complex silicon structures forming tan patterns. I've labeled regions of the circuitry. Circuitry blocks handle increment/decrement and latching of the three bits. Underneath, blocks compute the sum and multiplex the two values. There are irregular regions of deep blue at the right. These are not significant, just oxide that didn't get completely removed when I dissolved the metal layer with acid. A complicated schematic showing one bit of the stack register control. The left half is a flip-flop that can hold a bit or toggle the bit (for incrementing or decrementing). The right half is a multiplexer to select either the top-of-stack from the flip-flop or the sum. The summing circuitry is not shown, but uses a carry-lookahead adder.
December 9, 2025 at 6:38 PM
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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.
A diagram showing two inverters in a loop. On the left, the first inverter has a 0 and the second has a 1. On the right, the values are switched. Thus, the circuit can hold a 0 or a 1. A close-up of the silicon showing the circuitry for one storage cell. Each cell has two inverters. Each inverter has a transistor and a weak pull-up transistor. A transistor is formed when polysilicon crosses over doped silicon. The two inverters are connected to bit lines to read and write the cell. This connection is through two selection transistors, controlled by a vertical word line.
December 9, 2025 at 6:38 PM
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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.
The registers in the 8087 chip form a tall, skinny rectangle. The storage cells are arranged in eight columns for the eight registers. At the top are two tag bits, then 16 bits for sign and exponent, and then 64 bits for the fraction part of the number. The image zooms in on an 8 by 8 block of storage cells. For this image, I removed the metal layer with acid, so you can see the silicon structures underneath. The silicon appears pinkish-tan.
December 9, 2025 at 6:38 PM
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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...
A photo of the 8087 die under a microscope. The die is rectangular, with complex patterns in purplish-brown. The patterns consist of rectangular regions, striped regions in the bottom half of the chip, and other more irregular regions. At the right, two regions are highlighted in red: the registers and the stack control circuitry. Around the edges of the die, you can see the hair-thin bond wires that connect the chip to its 40 external pins. The complex patterns on the die are formed by its metal wiring, as well as the polysilicon and silicon underneath. The bottom half of the chip is the "datapath", the circuitry that performs calculations on 80-bit floating point values. At the left of the datapath, a constant ROM holds important constants such as π. At the right are the eight registers that form the stack, along with the stack control circuitry. The chip's instructions are defined by the large rectangular microcode ROM in the middle.
December 9, 2025 at 6:38 PM
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Standard cells sped up the design of the 386 and the chip was completed ahead of schedule. Pat Gelsinger was one of the key people behind the use of standard cells in the 386 processor. Decades later, he became CEO of Intel.
A standard-cell inverter as it appears on the die, along with a diagram explaining the layout. The die image has green lines of polysilicon over grayish rectangles of silicon that look a bit like Lego bricks. The diagram shows how the inverter is constructed from a PMOS transistor and an NMOS transistor
November 22, 2025 at 4:56 PM
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In standard cell logic, all the transistors are in orderly stripes. Except one that's out of place below, in the middle of the wiring region. What's going on? I think it's a bug fix. Instead of redoing all the circuitry, someone realized they could patch an extra transistor into an empty spot!
A close-up of two columns of standard cell logic. I dissolved the metal layers with acid for this photo, so you can see the silicon. Each transistor has a dark outline around it. The transistors are all in columns except for one lone transistor between the columns; it is marked with a red arrow. The photo also has a few large greenish regions. These are areas where I couldn't remove the oxide layer completely, so they can be ignored.
November 22, 2025 at 4:56 PM
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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.
A close-up of two standard cells in the 386. The cells are outlined with green boxes. The photo looks like dark brown horizontal and vertical lines on a tan background, with large and small circles in the boxes. The photo is mostly incomprehensible because of the density of wiring in the 386, but what it shows is a layer of horizontal wiring and a layer of vertical wiring (the stripes between the dark lines). The larger circles connect the two metal layers, while the small dots connect the metal layer to the silicon or polysilicon underneath,
November 22, 2025 at 4:56 PM
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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.
A close-up of standard cell logic in the 386 processor. The circuitry appears as four irregular dark bands, with horizontal and vertical connections in the regions between the dark bands.
November 22, 2025 at 4:56 PM
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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