OK - I was told they were mercury, but frankly, I have been sort of skeptical that mercury delay lines would still be used in new digital designs that late in the game. Wire makes far more sense.
-- Will On Sun, Dec 13, 2015 at 1:09 AM, Brent Hilpert <hilp...@cs.ubc.ca> wrote: > On 2015-Dec-12, at 7:13 PM, Eric Christopherson wrote: >> On Sat, Dec 12, 2015, Jon Elson wrote (in the big top posting thread): >>> >>> Later they got some >>> IBM 2260's, which were Zenith 9" TV sets and a keyboard connected to an >>> interface box in the machine room. Very primitive, but very interactive, >>> great for quick program editing and submission. >> >> I'm reading about those terminals and find it just fascinating how they >> used acoustic delay line memory to remember the pixels. But I have lots >> of questions: >> >> 1. Did the cables connecting the 2260s to the display controller >> actually contain the delay lines themselves, over the whole length; or >> were the delay lines just inside the controller and then some electronic >> signal was sent out to the terminals? > > The delay lines for the 2260 systems were magnetostrictive (not mercury) > acoustic delay lines, contained in the controller. > > Magnetostrictive delay lines were a somewhat common memory technique in the > 60s, they were used in other early CRT display terminals and in some > electronic calculators of the period. > They were an improvement over the mercury delay lines of the first > stored-program computers, easier to work with and not as temperamental. > > Speaking generally of the technique (I never worked on a 2848 controller, I > have worked on them in calculators): > > Magnetostriction is a characteristic of some materials in which the material > will physically expand or contract slightly in response to an applied > magnetic field. > Thus a solenoid with a core of magnetostrictive material going through it > acts as a transducer of electrical energy to or from mechanical (acoustic) > energy. > IIRC, nickel or a nickel alloy was the commonly-used magnetostrictive > material. > > Generated acoustic pulses are entered into one end of the delay medium (a > metallic wire line) to be picked up at the other end by another transducer, > so converted back to electrical energy, electrically amplified and restored > to account for losses and distortion from the traverse of the delay medium, > changed as appropriate (read/write operations) and re-entered into the delay > medium. > Some implementations sent the acoustic pulses longitudinally through the > delay wire (expansion/contraction or push/pull of the wire), some sent them > torsionally (twisting/rotating the wire). > > The whole point of course, is the much slower speed of acoustic pulses > relative to electrical pulses results in a much longer latency through a > delay medium of a given length and hence more (time for) storage. > > The delay wire is formed into a spiral/coil loop for compactness. > > If you're interested in some specifications and physical data of a 1960s > magnetostrictive memory, in this instance in a calculator, see the commentary > part way down the page here, beside the picture of the coiled delay line: > http://www.cs.ubc.ca/~hilpert/eec/calcs/Sony2500.html > These are from measurements and calculations I made on that delay line. > Or in summary: the acoustic pulses travel at 8140 Km/h, taking 1.6 mS to > traverse a delay wire 3.62 m long, providing storage for 1024 bits, each bit > occupying about 3.5 mm in the line. > This calculator uses longitudinal pulses, while the 2260/2848 apparently uses > torsional pulses. >
