Show us your junk!

For some reason, the company I worked for bought a used IBM1620 that used core memory. (built circa 1961) The computer occupied a large room and required a serious amount of power to run.

We used to joke that when the computer was turned on the lights in the building would dim.

That computer was a decimal computer (using BCD digits). The op codes were 2 digits. The core memory could hold 20,000 decimal digits.

Definitely magnetic core memory.  When I first graduated (1976), I went to work for a military systems development company.  The US military was in love with magnetic core memory computer systems (both large and small).  I went to one of the manufactures for a training class (operation/maintenance/programming). where we got to get hands on with the core memory.  We actually did some repair work (mostly just soldering the wires to the card edge connectors).

In the systems that we worked with, which were mostly vehicle-based systems, the core memory modules were one of the high failure rate items.  We had a few instances were we needed to extract data from the memory modules (potentially weeks of data collection) much in the same way that you might need to retrieve data from a crashed hard drive.  We would pop open the modules and attach/fix any leads and then attempt to run the system long enough to dump the data on to a magnetic tape drive (or sometimes paper tape).

Gene

Core memory indeed, good to see that it was recognized by so many people, luckily I'm not the only senior in this group.

If I remember correctly, it came from an oscilloscope with a memory function, sort of an early digital scope.

As promised a close-up:

very cool! is each one of the little black hoops a bit?

yes. You flip the magnetism by running a current through the matrix. If I recall well, a read operation is destructive and the bit has to be rewritten after a read.

The Cray Super computer was developed here in Chippewa Falls. Somewhere along the way I picked up this section of core memory from an early Cray machine. I would guess that it was in the middle to late 1960s. At the time they were still using discrete transistors in their circuits. There are 1024 bits in each of the 4 quadrants so this would be the equivalent of a 4 kb memory chip. My how things have gotten smaller.

John

John if I am not wrong, this technology was hand-made.

Hi Enrico,

Yes you are correct. They had a form that held the cores and the wires were strung by hand. I remember someone showing me the process a long time ago.

John

Well, at 4kBits ... that's 512-bytes or just under two "extra length" 280-character tweets assuming coded in 8-bit ASCII, perhaps just short of three if coded in 5-bit Baudot.

In fact, this message would consume about half of the array already.

- Gough

There is an Arduino shield kit available, if anyone wants to have a go at 'knitting' core store...

https://www.tindie.com/products/kilpelaj/core-memory-shield-for-arduino/