Interesting part

Tony Duell wrote: ... Back in the early 70s at Oregon State University, there sat a "home built" (using Naval Research funding) computer called "Nebula." (You can look it up - it's in many of the online histories/chronologies) Its memory consisted of 4k by 34 bit (yes, 34 bit) words made from Corning Electronic Devices glass delay lines (part number 853302.) These delay lines were 100us devices and, at about 27mhz bit rate, we stored around 2k bits per device. This resulted in 64 words of storage per card, so with 64 cards we achieved a whopping 4k words (16 kbytes) of storage. It was all DTL logic driven (as was most of the computer at that time) built from your basic 2n3406 and 2n3407 transistors, if memory serves. I fooled around with this machine from 1970 through the mid 70s, getting its small drum offline storage working and adding a few instructions, general maintenance etc. as well as writing a bunch of software. When computer time on this machine was "free" relative to the $300 / hr on the "big iron" it was an easy choice. The memory was quite reliable, not temperature sensative and would retain its contents indefinitely (as long as power wasn't removed, of course.) The 34 bit word layout consisted of 32 "numeric" data bits, plus a S ("spare") and P ("parity") bits. The 34 bits were all part of the programmer model. The "parity" bit was misnamed, since it really never was involved in a word 'parity' check and the "spare" bit wasn't really a "spare." Both were testable and setable but not involved in numeric or logical operations. The only changed on store and explicit set/clear operations. The machine also had 2k similar size words, made from basically the same glass delay lines, but organized as a content-addressable memory. The CAM was not usable as program storage, but you could store data there, after a fashion. As I said, the memory worked well and including the drivers and timing controls, was a comparable volume to core memory of the time. Of course, it was slow and serial (imagine a drum with a 100 uS rotation rate.) But since the machine itself (at the outset) had a 100uS cycle time, it was still "relatively" fast. We later (mid 70s) replaced the glass memory with a core storage module Nebula got one of it's core modules. This resulted in 32k words of storage with a cycle time of a few microseconds. Unfortunately Nebulas core control logic wasn't up to that speed (it was a serial computer by nature) so the best we ever got was about 30 uS word time (and that was pushing it a bit.) Short answer, glass was quite reliable. I still have one of the modules and want to build a small demo memory with it some day. Only wish I had enough to build a reasonable size machine... -Gary