Ken Shirriff's blog

Computer history, restoring vintage computers, IC reverse engineering, and whatever

An 8-tube module from a 1954 IBM mainframe examined: it's a key debouncer

IBM's vacuum tube computers of the 1950s were built from pluggable modules, each holding eight tubes and the associated components. I re...

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

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 nee...

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...

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 co...

Creating a Christmas card on a vintage IBM 1401 mainframe

I recently came across a challenge to print a holiday greeting card on a vintage computer, so I decided to make a card on a 1960s IBM 140...

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