Repairing the card reader for a 1960s mainframe: cams, relays and a clutch

Ken Shirriff writes: I recently helped repair the card reader for the Computer History Museum’s vintage IBM 1401 mainframe. In the process, I learned a lot about the archaic but interesting electromechanical systems used in the card reader. Most of the card reader is mechanical, with belts, gears, and clutches controlling the movement of cards […]

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

Ken Shirriff wrote a great article describing the repair process of  the vintage IBM 1401 mainframe computer: The problem started when the machine was powered up at the same time someone shut down the main power, apparently causing some sort of destructive power transient. The computer’s core memory completely stopped working, making the computer unusable. […]

Examining the core memory module inside a vintage IBM 1401 mainframe

Ken Shirriff writes: The IBM 1401 mainframe computer was announced in 1959 and by the mid-1960s had become the best-selling computer, extremely popular with medium and large businesses because of its low cost. A key component of the 1401’s success was its 4,000 character core memory, which stored data on tiny magnetized rings called cores. […]

Bitcoin mining on a 55 year old IBM 1401 mainframe: 80 seconds per hash

Ken Shirriff writes: Could an IBM mainframe from the 1960s mine Bitcoin? The idea seemed crazy, so I decided to find out. I implemented the Bitcoin hash algorithm in assembly code for the IBM 1401 and tested it on a working vintage mainframe. It turns out that this computer could mine, but so slowly it […]

12-minute Mandelbrot: fractals on a 50 year old IBM 1401 mainframe

Ken Shirriff writes: When I found out that the Computer History Museum has a working IBM 1401 computer[1], I wondered if it could generate the Mandelbrot fractal. I wrote a fractal program in assembly language and the computer chugged away for 12 minutes to create the Mandelbrot image on its line printer. In the process […]

A database of SMS cards: The technology inside IBM’s 1960s mainframes

Ken Shirriff writes: Although the original idea of SMS cards was to standardize on a few types, the number of different cards exploded as time went one, resulting in thousands of different SMS card types. As well as logic gates, SMS cards can have an amazing variety of functions such as an oscillator, voltage regulator, […]