ISA bus throughput

Tony Duell ard at
Thu Apr 13 15:07:28 CDT 2006

> On Thu, 2006-02-02 at 21:19 +0000, Tony Duell wrote:
> > ST506 is a low-level, raw, interface. What you see on the interface 
> > connectoer is essentially the pulse stream to/from the head. It's up to 
> > the cotnroller to turn that into the user data bytes/words.
> So, and I do know this is perverse :) - you could actually record, for
> example, audio onto an ST hard drive, and play it back? Of course, it'd
> just be a toy, but...

Not easily. You don't, of course, get the raw head connections at the 
interface connecotr, there's a write (recoding) driver and a read 
(playback) amplifier in the drive. These circuits are strictly digital 
(the interface signals are actually at RS422 levels IIRC). And there are 
resrictions on the frequency of the pulses you can record (both minimum 
and maximum from what I rememebr).

And of course, sioce the drive rotates at something like 3000rpm, you'd 
only get a recording time of 1/50 of a second per track.

I do have a video hard disk in my collection. This is a head-per-track 
hard disk rotating at 3000 rpm, such that 1 frame of TV video can be 
recorded on each track. It uses FM (analogue) modulation to do this. 
There are 3 indentical read/write circuits to handle RGB colour.

I am told that this sort of disk was oringinally designed for TV action 
replays. The one I have has a DAC on the input to the FM modulator, with 
a Unibus interface (via a DR11-B) on the front of that.


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