Gregory's ServerThe 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
Ken Shirriff
6 comments
Ken Shirriff
The computer uses numerous power supplies (some visible in the photo) to provide different voltages. Relay logic activates the supplies in order, checking voltages before activating more supplies. If a voltage is bad, the power-up sequence stops. 3/10
Ken Shirriff
These eight relays control the power-up sequence, closing circuits in order. The SMS card to the right checks one of the voltages. (Why relay logic? Probably because the power supplies for the transistor logic isn't energized yet. Chicken and egg.) 4/10 
Roger Sen
“Relay logic activates the supplies in order, checking voltages before activating more supplies.” I learnt it from my operating systems teacher: turn on the devices IN-ORDER.
kitlovesfsharp
@kenshirriff Ooo this reminds me of an anecdote which hardly anyone other than you will appreciate Ken! When I worked in the City of London in the 80’s/90’s, Wang systems were common. The disk drives were separately powered, with big push off/push on buttons. They didn’t actually power down until you pressed *and released* the button. 1/2
Tara Stella 🌷
@kenshirriff I had the privilege to see the 1401 in action in the museum last October. Thank you (and all volunteers) so much for keeping it running. 🙏 P.S. As a former Sun Microsystem employee, seeing only a few pieces was a pity, even if Sun was not far away. |
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