8 May
2007
8 May
'07
9:37 a.m.
Chuck Guzis wrote:
The only issue I have is that this is for an archival box, where it's probably
not a good idea to have ancient media spinning any longer than necessary. However:
1) I seem to find that if a disk is going to shed its coating [1] it does
so within the first couple of disk revolutions,
2) As above, usage of any such archival device probably doesn't involve
typically having more than one disk inserted at a time anyway, so the motors
are only on for the length of time needed to access that disk.
... so maybe I'm worrying about nothing.
[1] Grey-labeled 5.25" Wabash disks seem to be guaranteed to leave me with a
clear disk of plastic and drive heads caked in magnetic coating, regardless of
how they've been stored :-(
On 8 May 2007 at 4:30, Jules Richardson wrote:
I hear ya :-)
Some drives have speed control on one of the pins
(300/600 RPM, or 300/360
RPM), LED signal, motorised eject, disk change reset etc. - I suspect that it
doesn't hurt to have a few I/O lines set aside on the interface connector for
special cases.
One of the problems in engineering is knowing when to stop. DC37
connectors are not uncommon, exist in IDC versions (easy attachment).
50-pin D-subs are far less common. IDC headers aren't made for
frequent use and are subject to pin breakage and stress on the PCB.
That one is a good point. I suppose that's up to Phil as to where he's aiming
this. Personally I'd use it more as an internal board with lots of drives
permanently connected - but I do also like his scenario of being able to just
take it on the road with a laptop and a single drive connected.
I suppose in the latter situation it needs a case anyway though, and the
solution might be to have IDC headers on the board but taken out to the DC37
on the case for plugging into a drive.
Most of the signals you're talking about above are
slow signals--
Good point.
there's no particular need for those extra 5 pins
that I mentioned to
be paired with a return, so you could have 5 additional programmable
pins (1 input, 4 outputs?) if needed.
I know the Manta SCSI-floppy boards that I have are set up like that; I think
they have three programmable outputs and then another pin that can be
configured as either an input or output (I know the manual states that pin 2
was an input on some drives and an output on others)
But please let's not run power over the cable
Heh heh. Definitely agree there!
Wouldn't
you have to have motors running on four drives at once, though? I'm
not sure that it matters in practice though as for an archival box I suppose
you only have one disk in one of the drives at any one time...
Before IBM came along, there were plenty of systems that ran the
5.25" drive motors at the same time. IBM gave up 2 drive selects
with their twist and got to use a feebler PSU on the 5150. Some DTC
hard disk/SCSI controllers gave back 4-drive operation by using an
"untwisted" cable. I don't see that as a problem.