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Why is the RX50 how it is?

maxtherabbit

maxtherabbit

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What was the thinking behind making a "dual" floppy drive with 2 heads and one spindle? Literally the same parts count as a single double sided drive.

What was their reasoning behind this? People always talk about how it was 80 tracks to "compensate" for being single sided but why not just do DSQD?
 
Perhaps it was because double sided 5 1/4 floppy drives were still pretty new at the time? I think the IBM PC and MS-DOS didn’t fully support them until 1982.
 
Wasn't part of the reason so the customer would buy floppy disks from DEC only? As you could not format an RX50 disk on the Rainbow? Still an odd decision to me.
 
I think cost was a big driver in the design. DEC needed to support 2 disks to allow copying. 2 full size drives took up too much space.
Half hight drives were years away.

The engineering needed to make a dual disk single drive was a simple (sort of) task.
Basically redesign the spindle for 2 disks, and head assembly to support two heads.
Mirror image door latch and disk guides.
The parts count goes up a bit but nothing like 2 drives would.

The lack of formatting was common for DEC you could not format RX01 disks either.
I have dozens of boxes of 3m rx50 disks so DEC didn't get all the money.
 
Remember that the early double sided drives had many problems that single sided drives didn't. Having two single sided drives sharing a motor in a combined mount won't have the same difficulties. Apple tried something similar with the Twiggy drive with its pair of single sided read/write heads though Apple ran into a lot of other issues. In both the DEC and Apple cases, by the time RX-50 or Twiggy was ready to be shown in public, the drive manufacturers had solved the double sided design and even managed good slim line designs.

DEC did have a rather unfortunate desire to sell pre-formatted disks at a considerable surcharge enhanced by leaving out formatting tools. Of course, DEC being DEC, DEC made it trivial to add third party formatting tools.
 
Double-sided 5.25" floppies came after the introduction of single-sided ones. The RX50 makes sense in that it put two drives in the space of a single full-height drive. IIRC, there was also a (non-DEC) 8" drive similarly constructed.
 
Basically - no one stopped the guy who said "We could make our own cheaper - how hard can it be?" - there was another make with the same arrangement of drive doors and back-to-back disk orientation as well, maybe the inspiration or actual original design or manufacturer?

Not sure which is worse, trying to dismantle and reassemble one - or listening to one doing a disk to disk file copy...
 
Apple:
"For our next computer we will be using a revolutionary new floppy technology called "FileWare". With FileWare you can store over a megabyte of information on one floppy disk and using a drive assembly more compact than any of the competition on the market. That is because FileWare was designed here, in house at Apple!"

Dec:
"Guys, hold my beer and watch this."
 
krebizfan said:
DEC being DEC, DEC made it trivial to add third party formatting tools.
Click to expand...
Sounds like a case of the business people wanting to grab more money by forcing customers to buy their disks, but the engineering people knowing that people are going to want to do this on their own anyway.
 
Radix said:
Basically - no one stopped the guy who said "We could make our own cheaper - how hard can it be?" - there was another make with the same arrangement of drive doors and back-to-back disk orientation as well, maybe the inspiration or actual original design or manufacturer?

Not sure which is worse, trying to dismantle and reassemble one - or listening to one doing a disk to disk file copy...
Click to expand...
With both heads on a common assembly every time you selected the other disk you were guaranteed to be on the wrong cylinder.
It sounded like it was taking itself apart.
 
krebizfan said:
DEC did have a rather unfortunate desire to sell pre-formatted disks at a considerable surcharge enhanced by leaving out formatting tools. Of course, DEC being DEC, DEC made it trivial to add third party formatting tools.
Click to expand...

DEC sold pre-formatted disk because sys admins would buy them, and I can see the appeal.

If DEC supplied the disks and the drives, it was on them to guarantee they would work together. With third party media you got each side blaming the other. It also lowered the engineering requirements for the drives since they only had to hold speed for 300ish bytes when writing instead of a whole rotation when formatting.

CW
 
Bitly said:
DEC sold pre-formatted disk because sys admins would buy them, and I can see the appeal.

If DEC supplied the disks and the drives, it was on them to guarantee they would work together. With third party media you got each side blaming the other. It also lowered the engineering requirements for the drives since they only had to hold speed for 300ish bytes when writing instead of a whole rotation when formatting.

CW
Click to expand...
All the major system manufacturers sold preformatted disks. Not a problem. DEC did something unusual in refusing to equip many systems with a formatting tool so third party disks could not be used. That was very unpopular, in part because DEC took a long time to ship ordered product. Risking the formatting of a third party disk is a lot cheaper than shutting down the computers over a lack of disks.
 
Over the last year or so, I've processed overt 300 disks (mostly RX01, but some RX50), all DEC-labeled, mostly over 40 years old. Only one problem disk in the lot, and that was mostly due to someone storing the thing without protection to collect dust. The jacket liner was contaminated as well. Clean the disk, put a new jacket on and read with no errors.
Say what you will about DEC media, but I've found it to be quite reliable.
 
I guess that’s one way of attempting to assure quality control over the media. If you don’t let someone format any old disk, you have to buy quality disks from them.
 
On the other hand, there was particularly bad lot of Radio Shack/Tandy 8" SS disks that I swear were bad even before the shrink-wrap was pierced. I've heard that the suspect was terrible storage conditions in the Ft. Worth warehouse. But those buggers shed like crazy.
 
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