20 Oct
2006
20 Oct
'06
8:14 a.m.
Chuck Guzis wrote:
On 19 Oct 2006 at 15:28, Jules Richardson wrote:
Sure - I wouldn't want that either, I'd expect the motor to only be run during
each track read, though. Whether starting and stopping the motor n times to
read a disk is a good idea or not I don't know - it's more stress on the drive
for sure, but whether it's sufficiently more to warrant not doing it I don't
know.
What's the worst-case floppy rotation speed - 300rpm? So five revolutions per
second. Fastest transfer rate is 1Mbps (although didn't some PS/2 systems
manage two?) which in theory gives a maximum of 200Kbits for a track. But with
8x oversampling that'll be 200KB of data for a single sampled track read. So
roughly 18 seconds per track, given the port speeds you mentioned above.
That's slooooow. Given the nature of the data though, it'd probably compress
(using something like LZW) reasonably well - but then if driven by an old 8bit
CPU it may be that any compression (or decompression for write transfers) uses
up any time saved at the transfer stage.
I don't see what it would gain you, though.
You've still got the same amount
of data to transfer between host and device - and I bet someone can come up
with a situation where they'd want to just read or write a single track rather
than an entire image, which makes transferring an entire image wasteful
(particularly at RS232 speeds!)
I didn't say that transfers should be whole-image; just that the read
operation should be capable of transferring a whole image at a time.
Here's why.
Suppose the track image of a CW contains HD MFM data--worst-case,
you'll have something like 100K flux transitions to record. That's
100K bytes per track. Assuming you use 115K for your serial transfer
link, that's 10 bits per byte (8N1) or about 11K bytes per second,
so you can transfer the aforementioned track in 9 seconds, roughly.
160 tracks amounts to 24 minutes. That's more time than I want to
have the heads loaded and motor spinning with some aging floppy
that's barely hanging on to its oxide. When I work with floppies here, I usually read them at
most one-and-a-
half times. I then spend my head-scratching hours looking at the
image, not the original.
Yep, same here. I don't normally expect more than a couple of reads out of a
disk - although typically they'll do a *lot* more than that (at least for
5.25" media).
So, if the aforementioned hypothetical box can simply
suck up an
entire disk at full drive speed, so much the better for everyone.
I'm thinking that the "box built from junk PC bits" needs more investigation
(would make it easy to provide Ethernet support!). It depends what people
want, though - do they want a box to do data recovery from various floppy
media (which means a selection of drive types plugged in at once), or do they
want a backpack-like single drive solution (which implies they want something
compact, and the bulk of a scrap PC motherboard + PSU is too big)?
Personally I'd ideally want to throw at least 8", DD + HD 5.25", and DD + HD
3.5" drives in there - which in PC parlance probably means something like a
midi-tower case just to fit drives in, so compactness of the controlling
hardware isn't an issue.
cheers
Jules