Memory Tech you don't see very often

Paul Koning paulkoning at
Thu Jan 6 13:31:26 CST 2022

> On Jan 6, 2022, at 2:11 PM, Chuck Guzis via cctalk <cctalk at> wrote:
> On 1/6/22 10:17, William Donzelli wrote:
>> If you include prototypes, then you need to include ALL the prototypes
>> - even things made in single quantities that never worked.
>> That is a HUGE amount of stuff that makes EBAM look gigantic.
> To be fair, EBAM received a not-insignificant amount of press coverage.
> What doomed it was the falling cost and increasing density of
> semiconductor memory.  Good idea, wrong time.
> It was pitched in a few forward-looking responses to government RFPs.
> But then, so was a lot of other stuff.

So what is an EBAM tube?  Google turns up very little; I found a reference in a 1977 textbook (courtesy Google Books) that makes it sound like a synonym for "Williams tube".  Those were decades obsolete by then; so what were these things and why were they being considered in the days of not just semicondutor memory but also core memory?

Selectrons are weird devices, but just like (nearly all) core memory they use coincidence addressing to keep the control logic complexity reasonable, a very significant consideration in the days of vacuum tube logic.  And actually the addressing is even more clever so it scales with the 1/4th power of the memory size (same as core does if you put current switches at both ends of the X/Y wires).

A 1948 discussion of memory technology concepts makes fascinating reading; it includes wild stuff like photographic film and paper marked by electric discharge, along with familiar stuff like drum and acoustic memory.  But the drum discussion suggests that a drum might be spun at 60,000 rpm -- which would certainly do wonders for performance but it's puzzling where that dream came from.


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