Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!convex!iex!ntvax!yang1
From: yang1@ntvax.UUCP (cqyang class)
Newsgroups: comp.arch
Subject: Writable instruction set cpus
Keywords: cpu, 3b20d
Message-ID: <483@ntvax.UUCP>
Date: 2 Jun 89 04:08:58 GMT
Distribution: na
Organization: University of North Texas
Lines: 30



  We may have beat this to death already but...

  Is there anyone out there that has used an AT&T 3B20D minicomputer? As I
understand, this machine has a writable microcode section in it. It is used
by the telephone company to run with its 5ESS phone switching machines. The
reason it has a writable microcode section is so the machine can run programs
written for processors in provious switching machines. It also has a
permanent copy of the 3B instruction set to run 3B software. The other
instruction sets are loaded in when the machines boots. When running
with the 5ESS, it uses an operating system called DMERT. The computer
system can also be used as a reliable stand alone minicomputer. It has two
processor boards. It constantly monitors itself to check for faults. When one
is detected, a second processor board takes over, signals a fault, then takes
off where the first processor left. The faulty processor board, or any
other type of board that needs to be replaced, can be done while the machine
is still running. Software upgrades can also be done while the machine runs.

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