Vt 103 / lsi 11/23 marketed as a desktop late 1980

Jerome H. Fine jhfinedp3k at compsys.to
Sun Apr 24 19:56:15 CDT 2016

 >Ethan Dicks wrote:

>>Prior to that point, I had a VT103 with just 256 KB
>>of memory and a DSD 880/8 which had an 8 GB hard
>>drive / RX03 floppy drive in an external box.  So
>>there were other 3rd party solutions as well.
>8MB?  But otherwise, also nice.
DSD (Data Systems Design) produced both the DSD 880/8 and the
DSD 880/30.  The DSD 880/8 hardware used an 8 MB MFM drive
and included changes to the DL(X).SYS device drivers to pretend that
the DL drive was an RL02, but with just 8 MB.  The DSD 880/30
used a 30 MB MFM drive to emulate 3 * RL02 drives which, of course,
could not be removed.  Both versions had a single RX03 floppy drive -
used 8" RX01 / RX02 type media, but with two heads, one for each side
of the floppy media.  When the index hole is in the double-sided location
(about an inch from the single-sided location), the DY(X).SYS device
driver tests a bit in the CSR that double-sided operations should be
enabled.  For V04.00 of RT-11 in 1980, DEC included extra code
in DY.MAC which supported the use of an RX03 (double-sided)
floppy drive, potentially with the expectation that such a drive would
eventually be sold by DEC.  Unfortunately, that code included a bug
suggesting that DEC never actually tested the code.  And by 1983
when V05.00 of RT-11 was released, that extra code which supported
double-sided operations had been removed.  So even if DEC had been
considering the sale of an RX03 floppy drive, it seems that the decision
was reversed or abandoned.

In order to avoid having to punch the extra two holes in the jacket of
the media to enable double-sided operations, I added a double-pole,
double-throw switch into the circuit for the two detectors which determine
if a single-sided or double-sided media is present.  In the normal
position, a single-sided media is used as single-sided.  In the reverse
position, a single-sided media is used as double-sided media.  Of
more than a dozen different brands of 8" single-sided floppy media,
all but one brand supported being able to be LLFed (Low Level
Formatted) by the DSD 880/30 internal firmware as double-sided.

>I have a VT103 (w/TU58)... I did set up a simple 11/23 in it once, but
>I should see what I can do with a SCSI card...
If you are adding just a dual SCSI card, there is probably enough power
to also support an old 3.5" 50-pin SCSI drive.  There will be more than
enough room to place the drive at the bottom of the VT103.  I would also
make the SCSI cable long enough to support adding additional SCSI
drives (daisy chain) outside the VT103 so you can backup the internal
SCSI drive whenever you wish without having to get inside the VT103
each time.  For my own VT103, I also added a switch and a power
plug to allow me to power the internal hard drive (SCSI or otherwise)
from an external PC power supply so that the VT103 power supply
would have a reduced load, especially at power-up when the load
is highest.

Jerome Fine

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