> Jay Maynard wrote: > > > > > The limit is that the cylinder number is a halfword, and exceeding that > > breaks a LOT of things. There are even today things you can't put on a > > 3390-9 beyond cylinder 65535 (the JES2 spool dataset springs immediately to > > mind). > > > Minor nit. On MVS a single extent cannot exceed 65535 *tracks* and > a 3390-9 has 10017 cylinders (150255 trks). > > Theoretically, ckd architecture can support 65535 cyls, 65535 heads > (or trks/cyl), 255 blks/trk, each blk with a 255 byte key area and a > 65535 byte data area (which adds up to a fairly large number). > > Greg >
Not quite - the key for this purpose is included in the length of the data block. (65535 * 255 * 65535) is still fairly large. More than 2.3 Gbytes. Back in my time the maximum data length supported on any device was 32k-8, but I did hear of someone reading an entire tape written (by some metering device) as a single block. -- Cheers John Summerfield Microsoft's most solid OS: http://www.geocities.com/rcwoolley/ Note: mail delivered to me is deemed to be intended for me, for my disposition. ============================== If you don't like being told you're wrong, be right!
