In a message dated 12/31/2007 12:47:22 P.M. Central Standard Time, [EMAIL PROTECTED] writes >What was Fmt6 for ?
Originally in DOS/360 you could, and in some cases were encouraged to, allocate files so that more than one file would share the same cylinder numbers as another file. This was called split cylinder allocation. For example, File 1 could be tracks 0-9 of cylinders 100-199 and File 2 could be tracks 10-19 of those same 100 cylinders. DASD seek times were humongous in the 1960s, so it made sense that if a program's DASD access pattern involved very frequent references between two data sets that those two data sets should be allocated so as to minimize seeking. Switching between two tracks in the same cylinder has always been a more or less instantaneous electronic event. Even if you have to wait for a full rotation to get to the right place on that other track in the same cylinder, the elapsed time was significantly less than an average seek on the first several DASD models. Another thing IBM did in DOS/360 was to design software deliberately to access multiple files that would assume the data was allocated with split cylinders. Thus their recommendation to use split cylinders with certain programs, such as the DOS Assembler and Sort/Merge. Next came compatibility between a DASD volume created on DOS/360 and being able to access its data under OS/360. This is why OS/MVS/etc. had support for split cylinder allocation. Bill Fairchild Franklin, TN **************Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489 ---------------------------------------------------------------------- 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
