Computer Laboratory

Technical reports

A replacement for the OS/360 disc space management routines

A.J.M. Stoneley

April 1975, 7 pages

Abstract

In the interest of efficiency, the IBM disc space management routines (Dadsm) have been completely replaced in the Cambridge 370/165.

A large reduction in the disc traffic has been achieved by keeping the lists of free tracks in a more compact form and by keeping lists of free VTOC blocks. The real time taken in a typical transaction has been reduced by a factor of twenty.

By writing the code in a more appropriate form than the original, the size has been decreased by a factor of five, thus making it more reasonable to keep it permanently resident. The cpu requirement has decreased from 5% to 0.5% of the total time during normal service.

The new system is very much safer than the old in the fact of total system crashes. The old system gave little attention to the consequences of being stopped in mid-flight, and it was common to discover an area of disc allocated to two files. This no longer happens.

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BibTeX record

@TechReport{UCAM-CL-TR-3,
  author =	 {Stoneley, A.J.M.},
  title = 	 {{A replacement for the OS/360 disc space management
         	   routines}},
  year = 	 1975,
  month = 	 apr,
  url = 	 {http://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-3.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  number = 	 {UCAM-CL-TR-3}
}