Date   : Wed, 14 Dec 1983 23:21:03-PST (Wed)
From   : decvax!ittvax!sii!mem@ucb-vax
Subject: Jade Double-D mod

b
I notice there has been some discussion of the Jade Double-D board.  My
brother has the DD and has done some interesting things with it.  He has
added 30K of extra memory on the DD board, and rewritten (and re-PROM'ed)
the DCM (the disc control module which is the control program for the
Z80 onboard the DD) to make use of this 30K as a disc cache.  His new DCM
combines mru (most-recently-used) and rfu (recent-frequently-used)
algorithms to decide which sectors to keep in memory.  The rfu scheme
involves a sliding window of the last 1000 sectors to have been accessed.
This combination of algorithms results pretty much in keeping the desired
things in the cache.  For instance, when he is working on a program,
the steps may involve editing and compiling a program.  With a strictly
mru-based caching algorithm, the source file would appear in the cache
and get replaced by the compiler COM file.  With the recent-frequency
algorithm added, sectors from the source file have higher priority.
The same applies to frequently run programs (e.g. PIP), or an editor,
etc.

I suppose that anybody who is interested in this can mail to me, as
he does not have a usenet account.

Mark E. Mallett
{decvax | ittvax}!sii!mem