 How much trouble can one wire cause? The IBM 1402 Card Reader/Punch (1959) was a workhorse of the punch-card era, speedily reading 800 cards per minute. But the museum's card reader occasionally crunched cards and jammed, interfering with the demonstrations. 1/8 Intel's 8088 processor powered the IBM PC (1981), ensuring the continuing success of the x86 architecture. The PC team selected the 8088 largely because its system bus was similar to the Intel 8085 processor, which the team had used in the now-forgotten Datamaster computer. 1/8
Show previous comments
 @kenshirriff it seems strange to think that it wasn’t until the i486 (1989) that this line of CPUs had on-chip cache. But suppose I am comparing an 8088 CPU with 28k transistors to one with over 1.1m  @kenshirriff The 8 bit bus on the Intel 8088 made the IBM PC compatible with the peripherals available for existing 8 bit PCs. DEC even introduced a "Rainbow" with both an 8 bit CPU and an 8088 in the same PC, so it could run both old & new software.  @kenshirriff Thank you for these threads. They are always so fun and interesting to read. Punch cards used to be a key part of computing. The IBM 1402 Card Reader/Punch (1959) could read or punch hundreds of cards a minute. But the punch at https://twitter.com/ComputerHistory stopped punching the first 16 columns. An explanation of the punch unit and how we fixed it... 1/9 A punch card holds 80 characters, one per column. The holes in each column represent the character. Cards can be punched manually with a typewriter-like keypunch. Or the computer can punch cards at high speed through an attached reader/punch. 2/9  @kenshirriff First parse of that had me reading the Twitter.com still used punch cards. And nothing would surprise me about Twitter. The IBM 1401 was the most popular computer of the early 1960s, with over 10,000 built. Renting for $2500 a month, it made a computer affordable to medium-sized businesses. You can see one in operation https://twitter.com/ComputerHistory. But what if the computer suddenly stops turning on? 1/10 When you push the POWER ON button, the computer springs to life. But starting last week, it would power off as soon as you take your finger off the button. Something was going wrong with the power-up sequence. 2/10 An interesting military chip, built by UTMC in 1991. It's a transceiver for the MIL-STD-1553 serial data bus, a standard bus that is used extensively used in military aircraft and other systems. 1/18 The 1553 bus transmits data at 1 megahertz using 27-volt pulses on two wires. The chip receives bus data and converts it to digital (TTL) levels. The chip also transmits data on the bus, generating high-current pulses. 2/18 Here's an unusual chip, a 7400-series decoder implemented with a gate array. It has over 1500 transistors in orderly rows, but most of them are entirely unused. Why build a chip in such an inefficient way? Let's take a closer look... 1/13 This chip was built by Integrated Device Technology (IDT) in 1991 for a military application. It was mounted on a multi-chip module with EEPROMs on either side. 2/13 Intel introduced the 8088 processor in 1979. IBM selected the 8088 for the IBM PC, a moment in computer history that ensured the dominance of Intel and x86. To improve performance, the 8088 prefetched instructions. Let's look at the prefetch circuitry inside the 8088... 1/12 Modern processors cache megabytes of data so it can be accessed without waiting on slow memory. The 8088's prefetch queue held just 4 bytes, still enough for a substantial performance boost. When memory was idle, the 8088 would load upcoming instructions into the queue. 2/12  Intel introduced the 8088 processor in 1979. IBM selected the 8088 for the IBM PC, a moment in computer history that ensured the dominance of Intel and x86. To improve performance, the 8088 prefetched instructions. Let's look at the prefetch circuitry inside the 8088... 1/12 Modern processors cache megabytes of data so it can be accessed without waiting on slow memory. The 8088's prefetch queue held just 4 bytes, still enough for a substantial performance boost. When memory was idle, the 8088 would load upcoming instructions into the queue. 2/12 The Space Shuttle had a large teleprinter onboard so the astronauts could receive text documents. We want to get it working, but first some reverse engineering... 1/13
Show previous comments
 What would you say is the first microcomputer? The Apple I from 1976? The Altair 8800 from 1974? Perhaps Micral N (1973) or the Q1 (1972)? How about the Arma Micro Computer from way back in 1962. This compact 20-pound transistorized computer was built for space applications. 1/13 Of course the Arma Micro Computer is not a microcomputer by the modern definition, since it was built from transistors. But it was small enough to get the name "Micro Computer". It also shows that 1960s computers weren't all room-filling mainframes. 2/13  @kenshirriff I would say the first personal computer has the Kenbak-1, but that's not quite what you asked :P. @kenshirriff I would have said something in the PDP-8 family. Looks like the 8S had a desktop model (1966). But this beats the PDP-8 by a few years, and it's much smaller. The Bendix CADC is an amazing electromechanical analog computer that was used by fighter planes in the 1950s. Tiny rotating gears and cams performed mathematical calculations. Let's disassemble one of the special servomotors that powered the gears and see how it works. 1/16 The cylindrical motor/generators rotated shafts inside the CADC, with a feedback loop to determine the right position. The tachometer generator provided speed feedback to the control circuitry, slowing the motor as it approached the right position instead of overshooting. 2/16 The Bendix CADC is an analog computer used by fighter planes in the 1950s. It computed airspeed, Mach number, and other important parameters. I reverse-engineered how it performed these calculations with tiny gears, differentials, and cams. 1/12
Show previous comments
 @kenshirriff do you know if this is the same Bendix as the Bemdix G-15 (?) that Usagi Electric is restoring? @kenshirriff Thank you for sharing this. I wonder if the reason for doing things this way was for radiation hardening. The Intel 386 processor (1985) was a key step in the evolution of x86, moving to 32 bits as well as a CMOS implementation. A less visible design change is its use of standard cell logic (marked in red), building many circuits from standardized building blocks. 1/17 The 386 was originally scheduled for 50 person-years of development time, but it fell behind schedule. The designers made a risky decision to use "automatic place and route", letting software do some layout. This worked and the chip was completed ahead of schedule. 2/17 Intel's 386 processor (1985) was an important step toward today's computers, moving the x86 architecture to 32 bits. The chip came in a 132-pin ceramic package. There's more going on in this package than you'd expect. Let's take a look. 1/13
Show previous comments
@kenshirriff  @kenshirriff I worked intimately with the design and analysis of these PGA packages in my early career then. Interesting psychology anecdote – when you had a sample and you showed it to people (eg upper management) and told them explicitly do not touch the interior, they would find it irresistible and stick their finger into the inner die-attach surface and bonding pads anyway, ruining the part. It was very weird how they couldn't control themselves. Must. Jab. Finger. In. Package. Intel's 386 processor (1985) was an important step toward today's computers, moving the x86 architecture to 32 bits. The chip came in a 132-pin ceramic package. There's more going on in this package than you'd expect. Let's take a look. 1/13 Here's an X-ray of the 386 package. The pins are bright white. The gray square in the middle is the silicon die. Inside the package, the grayish traces connect the pins to the contacts surrounding the die. Thin bond wires connect these contacts to the die. 2/13  @kenshirriff tbh i can't see anything other than the bent pin, as i find those deeply upsetting lol This Soviet CMOS chip is a 4-bit counter, a copy of the Motorola MC14516B. I'll use it as an example of how to reverse engineer CMOS chips. 1/20 Since the chip is CMOS, it contains two complementary types of transistors—NMOS and PMOS—working together. They are built by doping silicon to form N and P regions. The NMOS transistors are constructed in a "well" of P-type silicon. 2/20 An interesting die from 1982, maybe IBM. This is a 128-bit static RAM, but not a normal RAM. This is a test chip to see how different transistor sizes perform in the RAM's read and write circuits. 1/8 Each RAM cell consists of two inverters in a loop, a standard design. Two pass transistors select the cell for reading or writing. This cell has 6 transistors so it is known as a 6T cell. 2/8 Fighter planes of the 1950s used the Bendix Central Air Data Computer, an electromechanical analog computer that computed with gears. In this thread, I look inside its pressure transducers that converted pressure readings to shaft rotations that turned the gears. 1/13 An aircraft has a pressure port to measure the static air pressure and a pitot tube to measure the total pressure due to speed. These were connected by tubes to the front of the CADC. 2/13  @kenshirriff so it's just a blowtorch with a slide rule spackled on to it? Here's a large power transistor from the 1960s. This transistor is from the pre-silicon era; it is built from germanium instead. I cut it open to show the complex construction inside. 1/8 This "alloy junction" transistor has a germanium wafer with a thick indium ring on the visible side and an indium disk underneath. The indium forms an alloy of P-type germanium. The ring is the emitter, the disk is the collector. The result is a PNP transistor. 2/8 Most chips are formed on a silicon wafer, but this RCA telecommunications chip is constructed from sapphire. It is a silicon-on-sapphire CMOS chip, with silicon circuits sitting on top of a thin sapphire substrate. 1/11
Show previous comments
@kenshirriff Fascinating ! 2 questions, if I may: 1) is that some type of input protection? 2) the datasheet states HDB3 outputs can source 10mA, whereas all other output currents are 1.6mA. So I went looking for larger drivers, but all outputs look similar. Am I missing something (maybe it's just that the design got revised?). Thanks for all those nerdily interesting posts 🙂  |
Gregory's Server
Debugging the card reader is tricky. The card reader is controlled by numerous relays, electromechanical switches that are prone to malfunctioning if their switch contacts get dirty. The photo shows rows of relays above a jumble of diodes and resistors. 2/8