That's a restriction of 16 heads in some circumstances. But the IEBCOPY says/implies they are complying with an apparent restriction that causes a 256 head limitation.
BFN. Paul. On Mon, 25 Aug 2025 21:44:13 -0500, Mike Schwab <[email protected]> wrote: >For normal volumes, CCHHR where each letter is 8 bits. >For EAV volumes this is defined to x'ccccCCChrr'' where each letter is 4 >bits. >rr = x'00'- x'FF' >H 'x'0' - x'e' (since 3390s have 15 heads). >CCCcccc is the cylinder number, >with CCC=x'000' (non-eav 1 to 64K cylinders 56GB) >to 00F (800GB EAV) and the cccc is x'0000' - x'ffff'' 0 to 64K tracks > >On Mon, Aug 25, 2025 at 7:44 PM Paul Edwards < >[email protected]> wrote: > >> I am interested in the "artificial device" described on page 330 here: >> >> https://publib.boulder.ibm.com/epubs/pdf/dgt2u140.pdf >> >> (for use by iebcopy). >> >> I am actually interested in PDSes, not PDSE, but I would >> expect that an artificial device is the same either way, and >> that I could use it for a PDS too. >> >> It is defined as: >> >> 65536 cylinders >> 256 tracks (heads) >> and the tracks are 16M bytes, which means that regardless >> of the blocksize, you can fit 255 records in it. >> >> According to that page, it is subject to limits described here: >> >> https://www.ibm.com/docs/en/SSLTBW_3.1.0/pdf/idad400_v3r1.pdf >> >> But I'm not sure which page is relevant. >> >> I see limits on page number 41, but that's 16 MB for a single disk. >> >> This artificial machine can do that in a single track! >> >> What I'm interested in is why the number of heads is limited to 256. >> >> I normally see CCHHR - so that should mean 65536 heads, the >> same limit as the cylinders. >> >> Any idea why the heads on an artificial machine are only 256, >> and whether that is documented as suggested by page 330 >> of the first manual? >> >> Thanks. Paul. >> >> ---------------------------------------------------------------------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to [email protected] with the message: INFO IBM-MAIN >> > > >-- >Mike A Schwab, Springfield IL USA >Where do Forest Rangers go to get away from it all? > >---------------------------------------------------------------------- >For IBM-MAIN subscribe / signoff / archive access instructions, >send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
