A blast from the past! An IBM 1620 was the very first computer I programmed, way back in 1969, likely a model 2. As part of a second year Applied Mathematics semester we were given a block of coding forms, a McCracken book on FORTRAN II and a list of problems to solve. There was no instruction on how to do this beyond reading the book, as far as I can remember. Someone punched cards from our coding forms and put them into the machine. We never actually got to touch the hardware, but we could look at it through glass windows.

That was a life-changing experience as it led to me dropping out of my Physics degree and eventually going into a computing career.

Shameless plug (and hopeful suggestion): every esoteric/ancient computer system deserves a page like this one (that I’ll eventually finish).

https://rbanffy.github.io/fun-with-big-computers/fun-with-vm...

BTW, I have updated the container images for VM/370 Sixpack and VM/370 CE today.

Most people programmed the IBM 1620 like in the rzzzwilson comment here: FORTRAN on punch cards, running out of reach in a closed machine room. But the 1620 did have a console terminal so it could be used interactively.

Somebody at IBM built an interactive APL interpreter that ran on the 1620, but it seems this was never released:

Experimental personalized array translator system https://dl.acm.org/doi/10.1145/364520.364573

Currently the title says "Web-based IBM 1620 emulator and IPL-V from 1963" until HN's title policy inevitably vandalizes it to remove the informative part. But, to give further context on IPL-V, IPL (I think actually IPL-IV) was key to some early AI research, but the main reason it's interesting in 02026 is that it's what inspired Lisp. It's a terrible programming language by today's standards, and the manual is a horrible slog, but you can see the seed of almost every programming language popular today in it.

I have heard that among older IBMers the 1620 (model 1) was known as CADET, for "Can't Add Doesn't Even Try".