What *was* the Tahoe?

Eric Edwards eekg at ix.netcom.com
Tue Nov 24 11:40:51 AEST 1998

The Power 6/32 Tahoe was a product of Computer Consoles Inc. (CCI).  The
internal codename was "Tahoe", as all the CCI processors were named after
lakes in the US (others I can remember were Erie and Huron).  It was
originally intended  to compete with the VAX-11/780 - depending on the
benchmark it was 5 to 10 times faster than the VAX and much smaller and

The base processor consisted of 5 boards - implemented with AMD 2900 series
bit slice processors, PLAs and 74F series parts.  Surprisingly the bit-slice
processors were used in the MMU - the actual ALU was 74F181s. It was a big
endian machine that was sort of a cross between a VAX and a Motorola 68K.
As mentioned elsewhere, it is rumored that if you swap the nibbles in the
instruction bytes they end up the same as the VAX...

I think it also had some odd features: the cache was on the processor side
of the mmu -- so it was indexed by virtual address and instructions were
cached in microcode form.

As guessed from the lack of boot blocks, there was another board in the
system -- the Console Processor (CP).  It was a 68000 based Versabus single
board computer.  The boot monitor understood BSD filesystems on both tape
and disk.  It basically loaded the microcode into the CPU, loaded the boot
image (/boot?) into memory, and then started the main CPU.

CCI ported 4.2BSD to run on the Tahoe and the changes were rolled into the
4.3-Tahoe version.  They also ran System V (including a dual processor
version) and CCI's own fault-tolerant Unix - Perpos.

I think the last of the Berkeley Tahoe machines ended up at Rochester
Institute of Technology's Computer Science House (http://www.csh.rit.edu).
Some guys up there were attempting to do some work with 4.4BSD and the

I can probably dig up more information if anyone needs it...

-----Original Message-----
From: SHOPPA at trailing-edge.com <SHOPPA at trailing-edge.com>
Date: Sunday, November 22, 1998 6:47 PM
Subject: What *was* the Tahoe?

>  What is the "Tahoe"?
>Tim. (shoppa at trailing-edge.com)

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