DEC Rainbow 100A

From: Allison J Parent <allisonp_at_world.std.com>
Date: Mon Dec 1 06:46:33 1997

<quite a few Rainbow user groups sponserred by DEC. Allison I'm sure,
<has all the specs and there is a downloadable systems site.

Actually I'm not current on the Rainbow and a few otehr would know where
the stuff is.

< Not being mini or DEC literate what is the RX50 format and what
<systems (platforms) is it used on ?

Basic RX50:

Single sided, ten 512 byte sectors per track soft sector and 80 tracks at
96 TPI for a total of 409kb formatted space per disk. It was DECs attempt
to get more density on low cost floppy. While the format worked the slow
dual spindle single positioner dual drive was a dog and internal pressure
made it's use manditory for many systems that would have gone with buyout
floppy drives like teac or sony. In the late 80s that would happen as
a result for the need for PC compatability (AT) and later lower cost and
more compact (3.5" 1.44mb).

The format is not half a 1.2mb drive as it's 250kbit MFM(same as 360k
floppy) and the spin rate is 300 rpm. It emerged whe DSQD drives were
being seen on CP/M-80 and the 16 bit systems of the time. Back then CP/M
could effienctly use a pair of 800k floppies cheaper than hard disk. DSQD
were 96tpi, 80 track 730->820k per drive and were essentially 360k drives
with 80 instead of 40 tracks. This format combo fell into disuse quickly
with poor acceptance due to the general chaos of 5.25" disk formats emerging
between 81-86ish. The driver of that chaos was the need for more space and
the still very high cost of then 5-40mb hard disks. The availability of
media for IBM XT 360k made it a pseudo standard.

It was introduced on the early 80s and used on most all DEC systems until
the late 80s when the VAXmate broke the mold by used RX33(1.2mb at
compatable) and later with 3.5" RX23(1.44)/24(720k) on the 3100 and PC
systems.


Allison
Received on Mon Dec 01 1997 - 06:46:33 GMT