Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!milton!whit
From: whit@milton.acs.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: New type of computer- no semiconductors
Message-ID: <1309@milton.acs.washington.edu>
Date: 9 Jan 90 09:59:55 GMT
Reply-To: whit@milton.acs.washington.edu (John Whitmore)
Organization: University of Washington, Seattle
Lines: 41
Keywords: Josephson junctions
Summary: Japanese made superconducting computer


	According to Electronic Engineering Times (25 Dec '89), a
group funded by Japan's MITI has built a four-chip computer in a
totally non-semiconductor electronic technology, i.e. superconducting
Josephson junction switching, with niobium devices.  The speed/power
product for this technology (previously explored in lead superconductors
by IBM) is very good; the Japanese group claims 6.2 milliwatts for
a 1 MFLOP machine.  RAM speed is about 500 ps (that's PICOSECONDS, meaning
thousandths of nanoseconds), and ROM speed 350 ps.  The total instruction
set is 128 of 'em, and by some standards, this is a RISC machine.
	The other two chips were the ALU/latch and the program
sequencer (it's Harvard architecture, by the way; 10 bit instructions
and four bit data).  The "1 MFLOP" figure is probably for 32-bit floating
point words, but I can't be sure from the article.
	Two interesting notes: the four-chip set is from a research
group with only five people; the announcement coincides with their
request for continued research funding (I think they'll get it).
	One use immediately springs to mind; space applications
are power-stingy, and require hardness against radiation (solar protons
as well as cosmic rays) which is difficult to achieve in silicon;
superconductors should function well in space, and they'd be easier
by far to cool (with a well built parasol, any old rock in space
will achieve 3.2 Kelvin temperatures, well under the superconducting
threshold temperature).  Maybe the next outer-planet probes will carry
a descendant of this machine.
	Of course, the computer only works in liquid helium, so
a significant barrier exists to connecting it with the outside world.
Also, the logic depends on magnetic field sensing; a tenth of a percent
or so of Earth's magnetic field leaking into the area of the chip
could erase EVERYTHING, so some state of the art magnetic shields
are a necessity (not difficult to build, though, given superconductors
to build 'em from).  The group's spokesman, Susumu Takada, says the
junctions are simpler to build than transistors; they haven't tried
making anything smaller than 3 microns yet, and the group hopes
to build much faster devices (to get reliable operation without
crosstalk, the picosecond speed of the ALU's components has
been deliberately slowed).  The future looks promising for this
technology.

I am known for my brilliance,             John Whitmore
 by those who do not know me well.