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Analyzing the vintage 8008 processor from die photos: its unusual counters

The revolutionary Intel 8008 microprocessor is 45 years old today (March 13, 2017), so I figured it's time for a blog post on reverse-engineering its internal circuits. One of the interesting things...

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Inside the vintage 74181 ALU chip: how it works and why it's so strange

The 74181 ALU (arithmetic/logic unit) chip powered many of the minicomputers of the 1970s: it provided fast 4-bit arithmetic and logic functions, and could be combined to handle larger words, making it...

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1950's tax preparation: plugboard programming with an IBM 403 Accounting Machine

Long before computers existed, businesses used electromechanical accounting machines for data processing. These one-ton accounting machines were "programmed" through wiring on a plugboard control...

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Reverse engineering the 76477 "Space Invaders" sound effect chip from die photos

Remember the old video game Space Invaders? Some of its sound effects were provided by a chip called the 76477 Complex Sound Generation chip. While the sound effects1 produced by this 1978 chip seem...

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One-hour Mandelbrot: Creating a fractal on the vintage Xerox Alto

.cite { font-size: 70%}; code {font-size: 100%; font-family: courier, fixed;} pre.bcpl {font-family: courier, fixed; padding: 10px; background-color: #eee;} I wrote a short program to generate the...

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Improvements to the Xerox Alto Mandelbrot drop runtime from 1 hour to 9 minutes

Last week I wrote a Mandelbrot set program for the Xerox Alto, which took an hour to generate the fractal. The point of this project was to learn how to use the Alto's bitmapped display, not make the...

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Bitcoin mining on a vintage Xerox Alto: very slow at 1.5 hashes/second

I've been restoring a Xerox Alto minicomputer from the 1970s and figured it would be interesting to see if it could mine bitcoins. I coded up the necessary hash algorithm in BCPL (the old programming...

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Inside Intel's first product: the 3101 RAM chip held just 64 bits

Intel's first product was not a processor, but a memory chip: the 31011 RAM chip, released in April 1969. This chip held just 64 bits of data (equivalent to 8 letters or 16 digits) and had the steep...

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Examining a vintage RAM chip, I find a counterfeit with an entirely different...

A die photo of a vintage 64-bit TTL RAM chip came up on Twitter recently, but the more I examined the photo the more puzzled I became. The chip didn't look at all like a RAM chip or even a TTL chip,...

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Inside the vintage Xerox Alto's display, a tiny lightbulb keeps it working

In this Alto restoration episode, we repaired a second CRT display, exercising our TV repair skills and discovering a tiny mysterious lightbulb that caused the display to fail in a strange way. For...

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The Xerox Alto, Smalltalk, and rewriting a running GUI

code {font-size: 80%; background-color: #eee;} Be sure to read the comment from Alan Kay at the bottom of the article! We succeeded in running the Smalltalk-76 language on our vintage Xerox Alto; this...

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Steve Jobs, the Xerox Alto, and computer typography

Steve Jobs gave an inspirational commencement address at Stanford in 2005. He described how his decision to drop out of college unexpectedly benefitted the Macintosh years later: Reed College at that...

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Identifying the "Early IBM Computer" in a Twitter photo: a 405 Accounting...

The photo below of a "woman wiring an early IBM computer" has appeared on Twitter a bunchoftimes, and it stoked my curiosity: what was the machine in the photo? Was it really an early IBM computer? I...

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Fixing the Ethernet board from a vintage Xerox Alto

A Xerox Alto system on the East coast had Ethernet problems, so the owner sent me the Ethernet board to diagnose. (After restoring our Alto, we've heard from a couple other Alto owners and try to help...

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Hands-on with the PocketBeagle: a $25 Linux computer with lots of I/O pins

pre {border:none;background-color:#eee;max-width:40em;padding:4px;font-size:80%;} code {background-color:#eee;font-size:80%;} The PocketBeagle is a tiny but powerful inexpensive key-fob-sized open...

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Decoding an air conditioner control's checksum with differential cryptanalysis

pre.irremote {border:none;background-color:#eee;max-width:30em;padding:4px;max-height:5em; overflow:auto} code {background-color:#eee;font-size:80%;} Back in 2009 I wrote an Arduino library (IRRemote)...

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Creating a Christmas card on a vintage IBM 1401 mainframe

code {background-color:#eee;font-size: 80%;} .gist table.lines { font-size: 12px; line-height: 10px; } .gist-data { max-height: 10em; } .gist-meta { font-size: 80% !important; } .gist .blob-num {...

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Repairing a 1960s-era IBM keypunch: controlled by mechanical tabs and bars

In this article I describe repairing an IBM 029 keypunch that wouldn't punch numbers. Keypunches were a vital component of punch card computing, recording data as holes in an 80-column card. Although...

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Repairing a 1960s mainframe: Fixing the IBM 1401's core memory and power supply

A few weeks ago, I wanted to use one of the vintage IBM 1401 mainframe computers at the Computer History Museum, but the computer wasn't working.1 This article describes the multi-week repair process...

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Xerox Alto zero-day: cracking disk password protection on a 45 year old system

code {background-color:#eee;font-size:80%;} We've been archiving a bunch of old Xerox Alto disk packs from the 1970s. A few of them turned out to be password-protected, so I needed to figure out how...

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