25 Jul
2014
25 Jul
'14
5:04 a.m.
From: Eric Smith <spacewar at gmail.com>
Date: Thu, 24 Jul 2014 20:22:30 -0600
Subject: microcode store (was Re: Looking to get into a Mini Computer...)
Early on, it was very expensive to use fast RAM chips for a microcode
store, so DEC used bipolar PROMs except on relatively high-priced
machines (e.g., KL10 and KS10), and if serious bugs were found, the
microcode PROMs had to be replaced.
The PDP-9 uses transformers to store it's microcode.
You can change the microcode by changing the routing of the wires
through the transformers.
http://www.ricomputermuseum.org/Home/equipment/dec-pdp-9/pdp-9-restoration/…
--
Michael Thompson
25 Jul
25 Jul
10:28 a.m.
On Fri, Jul 25, 2014 at 6:04 AM, Michael Thompson
<michael.99.thompson at gmail.com> wrote:
The PDP-9 uses transformers to store it's
microcode.
You can change the microcode by changing the routing of the wires
through the transformers.
DEC also made that available as one of the building blocks of the PDP-16 family.
The technology is commonly known as "core rope memory" or "wire braid
memory". It is also used for the control store of the Apollo Guidance
Computer (AGC) and one level of the control store of the HP-9100
desktop programmable calculator (the other level being an
inductively-coupled PC board memory). It can be viewed as a
smaller-scale, simplified version of IBM Transformer Read-Only Store
(TROS), as used in the System/360 Models 20 and 40 and the 2841 DASD
(disk) control unit. TROS was designed for better manufacturability.
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