On Tue, Oct 18, 2005 at 12:23:39AM -0400, Robert A. Rosenberg wrote: > When I was a programmer working on the Intercomm Teleprocessing > Monitor product, I wrote the routine that allowed the Archive to be > read backwards not only from Tape but DASD. It was fun to wrote the > code to allow the DASD records to be read in reverse order (IOW: If > there were 5 records on the current track, read them as 5, 4, 3, 2, 1 > before going to the prior track).
Hmmm. Sounds exactly like something conceived by a friend of mine in the 1970s but never implemented: BAM (the Backwards Access Method.) I can't remember whether BAM specified that just record order was backwards or whether each record was also read backwards. :-) > The trick was to read them using > BDAM (TTR) after using an EXCP that issued a CCW Loop that read the > CK Record IDs until it ran off end of the track thus determining how > many records were on the current track. Oh, ouch, that's not playing nice. Think about the performance hit from the double connect time. Not to mention the fact that you have to wait for most of a disk revolution to get the "next" = previous record. Of course these days memory isn't an issue so to do this today you'd just read the whole track once forward and hand out the records in reverse order. /Leonard ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
