User community subsets (Was: Bootable Model III disks...

Fred Cisin cisin at
Tue Mar 2 13:55:37 CST 2010

On Mon, 1 Mar 2010, Al Hartman wrote:
> C'mon guys... Nobody with a Model I and E/I with disk drives left it
> stock without a doubler of some kind...

not stock, but the add-ons were mutually incompatible.
Sorry, but I must take issue with being a "Nobody".
Not contesting the veracity of it, just taking issue with being a Nobody.

If you compare the number of machines sold, with the number of accessories
sold, there were a surprising number (in closets?) of machines without
add-ons, owned by NOBODY's

> and... If you had the LNDoubler, you could do 8" and 5.25" (and now
> 3.5") single and double density disks all with the same board.
> I don't know of any board that only added 8" without adding a Doubler as
> well. I'm not saying there wasn't one... I just don't know about it.

The Omicron 8" board AND the Parasitic Engineering (Howard Fullmer) did 8"
SSSD, but did NOT add MFM.  They used 1771s.  At the time, "doublers"
were not available commercially yet, although the Percom Data Separator
was becoming quite popular.  The Omicron CP/M board would only work with
the Omicron 8" board, NO OTHER 8" boards. It even had an additional
pigtail connecting the CPU and FDC sandwich boards.  If the Parasitic
Engineering board would work with other 8" boards, I never found a way to
make it work, although admittedly, I never disassembled its boot code to
look for port accesses, or other software switches.

> Percom, Tandy, LNW and Aerocomp made doublers. I think only the latter
> two supported 8" drives.

Yes, MUCH LATER, Tandy, LNW, Aerocomp? got into it.  There were YEARS when
Percom was the only choice, and by the time the others got into it, most
of us had switched over to 5150, etc.

"EVERYBODY had . . . "  was a common refrain.  But, it usually only
referred to a limited local subset of the community.
Community subsets were extremely common, and many/most microcomputer users
were only in touch with others with the same basic configuration they had.
But, since EVERYBODY did that, NOBODY acknowledged the existence of OTHER
user community subsets.

"EVERYBODY has after-market mods."
"EVERYBODY buys the machine fully expanded - it's cheaper that way."
"EVERYBODY buys the machine bare and expands it - it's cheaper that way."
"EVERYBODY uses the RS monitor on their Model 1."
"EVERYBODY has a clock calendar card. (5150)"
"EVERYBODY has a SCSI card."
"EVERYBODY has a SCSI card."
"EVERYBODY buys generic XT motherboards"
"EVERYBODY buys their generic XT motherboards bare and populates them"
"EVERYBODY uses a V20 for DOUBLE the speed."
"EVERYBODY runs their AT with a faster crystal. (Until IBM altered the
boot code)"
"EVERYBODY has 640K on their motherboard."
"EVERYBODY converts their Gavilan to DS."
"EVERYBODY has voice output."
"EVERYBODY has added a control key."
"EVERYBODY has replaced their model 1s with model 3s."
"EVERYBODY has model 4s, instead of model 3s."
"EVERYBODY who does graphics uses a Mac."
"EVERYBODY who uses VisiCalc uses an Apple ][."
"EVERYBODY has a ZIF socket for their joysticks (Apple ][)"
"EVERYBODY has joysticks, instead of game paddles."
"EVERYBODY has a Z80 card."
"EVERYBODY uses parallel printers, not serial."
"EVERYBODY uses 1200 baud."
"EVERYBODY rolls their own BIOS"
"NOBODY uses assembly language any more, nor ever will again" - Clancy &
. . .

Which of those were true for YOUR circle of friends?
Which other ones did I leave off?
Aren't some of those pretty stupid?
(Don't you hate rhetorical questions?)

> Any Model I equipped with a doubler should be able to copy a Model III
> bootable diskette.


Although I had half a dozen Percom Doublers, THREE of my 4 model 1s did
not have doublers in them for more than a few weeks each, before changing
to other mutually incompatible sandwiches.   Each one was also tested
STOCK before modification (well, at least booted once)

For TRS80 MFM, I mostly used model 3s.

BTW, one of the colleges had all of their model 3s CONVERTED to model 4s.
The price for conversion was ~$100 more than a new bare model 4.
"EVERYBODY has the conversion done."

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