history is hard (was: Microsoft open sources GWBASIC)

Guy Sotomayor ggs at shiresoft.com
Mon May 25 13:22:40 CDT 2020

On Mon, 2020-05-25 at 20:00 +0200, Liam Proven via cctalk wrote:
> On Mon, 25 May 2020 at 05:30, Fred Cisin via cctalk
> <cctalk at classiccmp.org> wrote:
> > 
> > 
> IBMs came with an installable driver called, I think, IBMCACHE.SYS.
> This used extended RAM (above 1MB) as a hard disk cache, without XMS
> or HIMEM.SYS or any of that. I played with it and was amazed by the
> results. I started enabling it by default on customers' machines. 

I hadn't thought about IBMCACHE.SYS in *years*.  I wrote it in its
entirety (there's even a patent that covers some of its operation). I
was in an AdTech (Advanced Technology) group at the time and was
looking at how to make disk operations faster in DOS at the time when I
came up with the idea.

There was a *huge* battle within IBM on if it should be released and in
order to do so, it was fairly well hidden.

> Most
> were happy but some had the habit of just turning off -- DOS didn't
> really have a shutdown routine. Some, I could train to press
> Ctrl-Alt-Del before turning off. Some I couldn't, so I had to disable
> the disk cache.

There was a switch on config.sys statement for IBMCACHE.SYS to turn off
the write-back cache (e.g. writes would always go straight to disk). 
As I recall, there was a 30 second timer for the writeback cache so
that if a disk block was "dirty" for more than 30 seconds it would get
flushed to disk.

> But for those that could learn and adapt, it made DOS _much_ faster,
> and on a 1MB PS/2 Model 50 or 60, it was about the only thing you
> could do with the extra 386 KB of RAM before MS-DOS 5 came out.

TTFN - Guy

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