The Teletype Model 40 also used a spinning belt that held type slugs (IIRC, the same ones that the Model 28 used back in the 1950's). Only it was a rubber belt not a metal chain, so it didn't require hearing protection to run with the covers open. ;)
Based on the text content of the line you were printing, the sound would change from a "brap" (not many duplicate letters on the line) to a "braaaaaaaaaap" when you had lots of the same character, like when someone used the equal-sign as a section separator between paragraphs.
One location on the belt held a metal flag not a type element, and that was how the electronics knew the start of the type element sequence. One of the fun pranks you could do was to swap a couple of the type elements...
I'm a huge fan of Ken's Blog and Marc's YouTube channel but I am curious: were these IBM devices this unreliable in the past, or is it just old age? I feel like they are fixing stuff on these machines weekly.
The 1401 restoration team gets together once a week to maintain the machines. IBM mainframes were generally very reliable when new‡, but not surprisingly after 56 years these machines are not as reliable. The mechanical parts have experienced wear and rubber parts have lost elasticity. One of the 1401s was stored in an unheated garage in Germany for years and suffered significant corrosion (i.e. transistors that fell apart from rust). So there are always things to fix.
‡ The IBM 360/50 was apparently less reliable. The joke was that if you threw a Model 50 into the Hudson River, it would sink intermittently.
The funny thing is that while most of the IBM 1401 stuff (such as punch cards) is long obsolete, green-bar paper is still a thing - we simply buy boxes at Office Depot.
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[ 3.0 ms ] story [ 22.0 ms ] threadBased on the text content of the line you were printing, the sound would change from a "brap" (not many duplicate letters on the line) to a "braaaaaaaaaap" when you had lots of the same character, like when someone used the equal-sign as a section separator between paragraphs.
One location on the belt held a metal flag not a type element, and that was how the electronics knew the start of the type element sequence. One of the fun pranks you could do was to swap a couple of the type elements...
‡ The IBM 360/50 was apparently less reliable. The joke was that if you threw a Model 50 into the Hudson River, it would sink intermittently.
The first part of my career was spent studying green-bar. It's how programs were read, understood, and core-dump-repaired if necessary.
I guess we're lucky things got better online. Saving a lot of trees!