GB1418837A - Method and apparatus for searching and adding records to a sequential file in a small computing system - Google Patents

Abstract

1418837 Digital storage systems BURROUGHS CORP 18 June 1973 [3 July 1972] 28762/73 Heading G4C A sequential file in a slow access store is associated with a fast access store in which there is set up an index table which is used in the locating of a required record in the file. The index table comprises key words indicating the boundaries of partitions into which the file is notionally divided, each such partition containing a number of records. If a required record is not in a selected partition records added to the file subsequently to the formation of the partitions are searched. The accessing and the assembly of the table are controlled by a program controlled processor. Prior to the file being accessed a number NP is calculated. NP is the number of records in a partition of the file and is (MX/C) + 1 where MX is the known number of records in the file and C is the number of indexed (or keys), each of which defines a partition. The key of the ordinal number of the NPth record, i.e. of the record at the end of the first partition, is now read and is stored in the first location of the fast access store. The key of each succeeding NPth record is similarly recorded in successive locations until the index table is complete. To locate a required record a search is first made through the table. The search routine (Fig. 5A, not shown) determines the locations in the fast access store of the key of the partition containing the record and of the preceding partition. The location numbers are converted to record numbers by multiplying them by NP (Fig. 5B, not shown). The higher number is incremented by one and the lower is decremented by one. The keys of successive records in the partition so defined are now compared with the search argument until the required record is found (Fig. 5C, not shown). However should the record not be found in that partition those records that have been added to the file after it was opened are now searched. Such added records are later sorted into sequences.