In a message dated 3/29/2006 12:07:09 P.M. Central Standard Time, [EMAIL PROTECTED] writes:
>The DOS footprint bit? It _was_ mapped at one time. DS4DIRF or something like >that. DOS could happily use an OS/360 volume but didn't maintain the Formet 3s. >We used to switch 2311volumes between OS and DOS systems - if OS found the >DIRF bit (also called the "Dirty Bit") on it would recalculate the F3s before starting >allocation. It was a useful feature,and we used to ZAP the bit on every now and then >as part of housekeeping. >In faact I think even OS used to set it on before allocation and clear it afterwards. Correct. The acronym stands for DASDM Interrupt Recording Facility. The bit is (or was) turned on at the beginning of a long process in which multiple DSCBs had to be updated. When all updates were done, the bit was turned off. If on a new allocate the bit was found to be on, then DADSM knew that the free DSCB chain was not necessarily correct, so DASDM would automatically rebuild the format 3 DSCB chain. It was called the dirty bit because (a) "DIRF" sounds a lot like "dirt" and (b) the F3 DSCB chain was possibly dirty/contaminated/non-kosher/hosed if the bit was on. When you wanted to force a cleanup, you would IMASPZAP the bit on, then allocate something - anything - like a one-track data set with DISP=(NEW,DELETE) just to force DASDM to rebuild the F3 chain. Bill Fairchild ---------------------------------------------------------------------- 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
