Standard means that all block sizes are the same, except for possibly the last one, which might be short.
Spanned means that a single logical record might span multiple physical blocks, but the way it is implemented results in having all block sizes be the same, except for possibly the last one, which might be short. In either case, the DCB attribute byte and bit setting are the same for both uses of 'S', allowing all access methods have only one place to test for the 'S' attribute and thus are able to build channel programs slightly differently and thus often running slightly faster. At least that was true in the 1960s when these concepts were invented, but maybe not so true now with device-level buffering, inter alia . Bill Fairchild Franklin, TN ----- Original Message ----- From: "Ted MacNEIL" <[email protected]> To: [email protected] Sent: Wednesday, June 5, 2013 9:42:32 PM Subject: Re: I/O Optimization >Where does "spanned" come into play? Why does that make the difference? An acronym conflict! I hate IBM's tendency to use the same letters (in the same position) to mean different things! vbS -- Variable Blocked Spanned fbS -- Fixed Blocked Standard (BTW: why "Standard"? What the H-E-Double-Toothpicks does that mean?) They did a similar thing with: PCB -- before I ever even became aware of IMS it meant (to me) Printed Circuit Board. ATM -- I thought it meant Automated Teller Machine. - Ted MacNEIL [email protected] Twitter: @TedMacNEIL ---------------------------------------------------------------------- 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
