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Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!ucbvax!ucdavis!lll-crg!seismo!brl-tgr!tgr!campbell%maynard.UUCP@HARVARD.ARPA
From: campbell%maynard.UUCP@HARVARD.ARPA
Newsgroups: net.micro
Subject: NEC V20 chip (8088 replacement)
Message-ID: <1495@brl-tgr.ARPA>
Date: Sat, 14-Sep-85 07:04:09 EDT
Article-I.D.: brl-tgr.1495
Posted: Sat Sep 14 07:04:09 1985
Date-Received: Tue, 17-Sep-85 05:12:56 EDT
Sender: news@brl-tgr.ARPA
Lines: 33

I just put a V20 in my DEC Rainbow (running VENIX).  When you power up
the machine, you get a "Main board - MESSAGE 29" error, which appears
to be caused by the boot code waiting for the Z80 to respond "Yes, I'm
OK".  Since the V20 drops through the timing loop faster than the
8088, it thinks the Z80 is dead.

However, the Z80 still works, floppies still work, the system boots
VENIX and runs fine (also boots MS-DOS and CP/M; I did try them).  The
system feels slightly snappier; benchmarks show things running from 5%
to 100% faster.  The 5% was on floating point benchmarks (I have an
8087); the 100% was on a program to calculate the first 1000 digits of
e using a Taylor series.  General speedup seems to be around 15-20%.

I was able to get a measurable increase in disk throughput by modifying
the driver.  The V20 has INS and OUTS instructions (NEC calls them INM
and OUTM).  Using these instructions to copy data in and out of the
sector buffer gained about 10-20% in disk benchmarks.

The disk read benchmark (from Byte, August 1984) actually ran SLOWER
by about 5% before I hacked the driver.  After the switch to INS it
ran 28% faster.  This was the only test program that ran slower on the
V20.

Oh, a local distributor (Gerber Electronics) is selling them for about
$11, quantity one.

Larry Campbell                     decvax!genrad
The Boston Software Works, Inc.                 \
120 Fulton St.                 seismo!harvard!wjh12!maynard!campbell
Boston MA 02109                         /       /
                                   ihnp4  cbosgd

ARPA: campbell%maynard.uucp@harvard.arpa


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