19 Oct
2006
19 Oct
'06
3:24 p.m.
On 19 Oct 2006 at 15:28, Jules Richardson wrote:
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.
Granted, these are back-of-the-envelope calculations, but you get the
general idea.
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.
So, if the aforementioned hypothetical box can simply suck up an
entire disk at full drive speed, so much the better for everyone.
Cheers,
Chuck