On Thursday 02 February 2006 04:19 pm, Tony Duell wrote:
Yes, this
would be interesting. I had never realized that IDE was a
superset of ST506. Now I'm thinking of all of the old 8 bit machines I
have that could use
It's not. IDE and ST506 are very different interfaces.
IDE ias a formatted interface. You transfer nice 8-bit bytes and 16 bit
words to the drive. The drive takes care of turning them into a suitable
pulse train to send ot thehead, etc.
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.
The origianl PC/AT controller talked to an ST506 drive. But of course it
also had a host-side interface -- it plugged into an ISA slot and
appeared as a number of I/O ports to the 286 (or whatever) processor. The
controller card did the translation betweenn the user bytes/words and the
pulse stream on the ST506 interface connector.
Now you could also split the system up in a different way. Specifically,
move most of the controller over to the drive. The 'controller card' now
becomes little more than an address decoder which lets the host processor
talk to I/O port registers physically located in the drive. To the host,
it looks the same as the old ST506 controller (you send the same bytes to
the same ports to read a particular sector). Inside the drive, who knows
what goes on.
That's IDE.
It's not the _interface_ (as in hardware) that's got parts in common, it's
the command set. Which is one of the reasons we keep bumping into size
limitations.
<...>
Just because an IDE drive looks the same to the host
as one particular ST506
controller doesn't mean that all ST506 controllers look the same. They
don't.
The way it looks to the host is exactly the point. And how different are
they? The main thing I remember having to do with those early HD cards is to
use the BIOS routines that were on the card (in XT-class stuff) to format the
drive. AT-class stuff and later didn't have any BIOS on the cards, the MB
BIOS took care of that, so there must have been a lot of it which was the
same.
--
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ablest -- form of life in this section of space, a critter that can
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Information is more dangerous than cannon to a society ruled by lies. --James
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