Tony Cole's Cray-1

From: Allison J Parent <>
Date: Tue Apr 28 08:07:08 1998

<>The Cray-1 was ECL-10k fast for it's time but low density and rams for
<>that technology were 1 or 4k ECL bipolar. ECL had several
<>characteristics, FAST, high power consumption and low density.
<Excuse my ignorance, what does ECL stand for?

ECL or emitter coupled logic is a form is bipolar logic that operates
at low levels and is non saturating. Non saturating is where the active
devices are neither fully off or fully on. Logic levels are referenced
to a bias level so translation to MOS/CMOS/TTL is required. The reason
for doing non-saturated logic is speed, transistors have a problem like
tubes of charge storage making them harder to turn on or off and reducing
speed. Generally speaking from the late '60s through the '80s ECL managed
to be a factor of 5-20 times faster than the prevailing logic system(RTL,
DTL, TTL) until sub-micron CMOS started to get under 10ns. The last ECL
parts I looked at(years ago) were sub 1nS and could be clocked faster than
1000mhz. An example of the speed difference is 1974 the fastest TTL
divide by 10 (7490) was maybe 35mhz, ECL divide by 10 was 500mhz.

Received on Tue Apr 28 1998 - 08:07:08 BST

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