EEVblog 1713 - CRAZY Density Magnetic Core Memory! - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: October 06, 2025, 12:09:15 pm
content: A look at the crazy ferrite core density in the Ampex 1600 16k x 18 bit word magnetic core memory from Ampex Memory Products Division.00:00 - Magnetic core memory01:52 - How magnetic core memory works07:12 - Ampex high density 16Kword core memoryMagnetic core simulator:https://nationalmaglab.org/magnet-academy/watch-play/interactive-tutorials/magnetic-core-memory/#:~:text=Magnetic%20core%20memory%20was%20developed,electric%20current%20in%20a%20circuit.

author: axantas
author_rank: Regular Contributor
timestamp: October 10, 2025, 07:43:39 pm
content: I remember these boards. I had the chance to attend a proud presentation - aaaaaages ago - about memory in a mainframe. I must admit, I was impressed, as I was now with that flashback to old times - thanks Dave, enjoyed the video.Interesting fact, that we have some Schrödingers Cat in there, with destructive reading the 1 - I was not aware of this fact, but it makes sense.

author: EEVblog
author_rank: Unknown
timestamp: October 11, 2025, 04:22:07 am
content: Original mailbag:

author: Jan Steinman
author_rank: Contributor
timestamp: October 13, 2025, 05:54:09 pm
content: You questioned the "unusual" word size of 18 bits.I believe the extra two bits were used for cyclic redundancy checking (CRC).I worked for Tandem Computers in the 1980s. They were "fault tolerant" computers. Through a combination of redundant hardware and specially-written software, they could withstand any single component failure and continue operating unimpeded. Upon a new installation, our final acceptance test included a power-down of an arbitrary processor in the middle of running an arbitrary program, and the program had to continue unimpeded. We customer engineers would actually replace faulty components (board-level) on a functioning customer system, without affecting operations. This was actually quite a feat in those days! One of my clients was the NASDAQ stock exchange.As I recall, Tandem computer memory had an 18-bit word length, of which sixteen bits were used by the processors, and the extra two bits implemented the CRC in hardware. We were told it could detect any two-bit error, and actually correct any one-bit error. Such errors were logged, and we could replace a faulty memory board without even impacting running software.(Aside: before working for Tandem, I worked in the 1970s for a US Defence Department contractor. This was before the days of rotating hard disk memory, and we had something that took up about 18" of rack space that was a "drum memory". I never got a look at the innards or saw a schematic, but as I recall, it also used 18-bit words with CRC, and could store nearly a megabyte.)Yours truly, on the right.

author: golden_labels
author_rank: Super Contributor
timestamp: October 17, 2025, 11:27:26 pm
content: These are ferrite memory blocks from Odra 1305, a Polish computer from the 70s:Single moduleMemory bankUnfortunately I do not know the scale and I think I didn’t see any of these exposed last time I was at the museum. But we may estimate the density is quit high from other objects on the photo. The loupe and the text, likely 16–18 pt or so, in the upper right corner.With computing power in the range of hundreds OPS, the last two specimen in active use were shut down in 2010.This is an earlier model (Odra 1002).Look closely at the rightmost cabinet. This is the power supply and yeah, these transformers are enormous!