All I though I'd start a new thread with this subject so those searching index can find it.
My first and most memorable practical introduction to bit maps came from the Houston Automatic Spooling Program (HASP) in the early days of OS when it took several seconds for OS to read a few JCL cards, interpret, allocate files, and start a program. HASP the predesssor to JES2 was a subsystem which took over all the card readers and printers and spooled I/O to disk so application programs would run faster using disk and the printing could be done separately. The really cool part of HASP was how fast it was, and part of that speed came from using bit map for all of its disk space. Allocating a new track for printer output for a job consisted of turning on a bit as opposed to updating DSCB's on disk. And yes HASP did have a checkpoint restart facility including the bit table. So on a z196 the new bit counting instruction could be used to more easily count allocated tracks and report total spool space in use. Don Higgins [email protected]
