Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!ames!ucsd!dog.ee.lbl.gov!beva.bev.lbl.gov!wbrown
From: wbrown@beva.bev.lbl.gov (Bill Brown)
Newsgroups: sci.electronics
Subject: Re: What's a shmoo plot?
Message-ID: <11986@dog.ee.lbl.gov>
Date: 11 Apr 91 05:06:10 GMT
References: <7905@uceng.UC.EDU> <1652@spim.mips.COM> <57167@sequent.UUCP>
Reply-To: wbrown@beva.bev.lbl.gov (Bill Brown)
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 23
X-Local-Date: Wed, 10 Apr 91 22:06:10 PDT

'Way back in the olden days, when computers were built out of REAL
transistors and resistors and capacitors and stuff instead of all those
little bug-looking IC things, there was something called "core Memory"
which consisted of little ferritte (sp?) donuts strung on wires.

Several wires ran thru each donut, x-drive, ydrive, inhibit drive, and
read.  One computer I used to help babysit had really flakey memories.

In an attempt to keep it working, every week we had to mess with the
memory drive currents.  This usually consisted of tweaking the x & y drive
currents and observing where we started to pick up or drop bits.  These
points were recorded on a piece of graph paper.  When we got done the picture
really did look a lot like a schmoo.  We then eyballed the center of the
schmoo and set the memory drive currents accordingly.

I'm not going to try to draw a picture - but it really did look like
a (somewhat warped) schmoo.  I never understood why the bumps for the feet
and head showed up, but they did.

Disclaimer:  These opinions are my own and have	    |
    nothing to do with the official policy or the   |  -bill
    management of L.B.L, who probably couldn't      |   wlbrown@lbl.gov
    care less about employees who play with trains. |