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 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.
