At 10:49 PM 9/23/98 +0200, Daniel GAUDRY wrote: I need a good polyphase merge sort for VERY large disk files. I read about it in quite a few programming books but they never go to the end (no source code) and stay clear of doing so!!!!!, however it is what I need.Is there somebody who has one or knows where I can find it. Hmmm. First, I don't think that a polyphase merge sort is what you want when working from disks, since they are usually treated as random access devices. A carefully implemented heap sort may result in the fewest disk reads. Or it may be that a key sort is the way to go. (Read all the keys into memory, with a pointer into the file to the record. Sort the keys, then write the sorted file in order.) But the real answer is to use the Cobol sort command, interfacing via the Annex B stuff, and let the sort library provided with the Cobol implementation do its stuff. These sort libraries are very complex, and do take into account the amount of disk and main memory available when the sort is called. Robert I. Eachus with Standard_Disclaimer; use Standard_Disclaimer; function Message (Text: in Clever_Ideas) return Better_Ideas is...