On 2015-12-01 02:06, Jerry Weiss wrote:
On Nov 30, 2015, at 6:35 PM, Paul Koning <paulkon...@comcast.net> wrote:
On Nov 30, 2015, at 4:45 PM, Fred Cisin <ci...@xenosoft.com> wrote:
Oversimplified remedial tutorial:
Ideally, the system reads a sector, does what it has to do with the content,
and goes back for the next one, and can read every sector of the track in a
single revolution.
From: "Paul Koning" <paulkon...@comcast.net>
Your writeup was aimed at floppy disks, but interleave may also appear on hard
drives. I don't remember it in reasonably modern systems, but it shows up on
CDC 6000 systems.
On Mon, 30 Nov 2015, Mike Stein wrote:
----- Reply ----- Definitely an issue with IBM PC/XTs and clones; I recall
testing every new combination of HD and controller for most efficient
interleave before I delivered to the client.
1) Are there any examples newer than PC/XT 5160?
Although, obviously, completely hidden from the user, is it still used on anything
"modern"?
(Should ALL verbs be changed to past tense?)
2) Is it used on anything besides spinning rust?
Not that I know of.
I remember using interleave on SAN systems with (S)ATA drives, back around
2002-2004 or so when ATA and/or SATA did not yet support command queueing. So
you could only issue one command per drive, then in the interrupt handler you'd
have to handle the completion and issue the next. It turns out you could not
do that without interleave, or something analogous. For example, you can leave
the sector addressing unchanged but break transfers up into sectors, and issue
them in interleaved order. Similarly, when sorting commands offered by
applications, you can order them in this manner for the subset of commands for
a given track.
3) Besides all of my examples being floppy, what else should be
changed/corrected in what I wrote?
The only thing I would change is to mention that this is/was found on hard
drives also.
paul
The TU58 was a block addressable using a cassette tape drive famously(?) called
DECtape II. File placement on the two different linear tracks was a necessary
art, especially if you were booting RT11 regularly. This helped it to stream
or not rewind in sensitive places. The 1:2 interleave was “built-in” to the
block formatting (see EK-0TU58-UG-001_TU58_DECtape_II_Users_Guide_Oct78.pdf).
I wasn't aware that it did any block interleaving. But yes, file
placement was extremely important. Are you sure it interleaved blocks?
I used a late model device, pulling data from clinical diagnostic computers
without too many challenges. However, compared to reliability of DECtape*,
DECtape iI was not in the same class IMHO.
Jerry
*Yes - I skipped over DECtape. I’ve leave that one to the many experts on the
list.
DECtape never did interleaving that I know of. But there too, file
placement was very important. I don't think it would even work if you
interleaved the blocks, as the tape driver normally figured out which
was to spool depending on the current block at the head, and which block
you wanted to get to.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
