GB1314781A - Data processing apparatus - Google Patents

Abstract

1314781 Sorting digital data INTERNATIONAL BUSINESS MACHINES CORP 29 Sept 1971 [31 Dec 1970] 45279/71 Heading G4M Data processing apparatus is arranged to sort data into strings, which are subsequently merged to produce a single sorted output sequence, using a fist storage area with a capacity of LL records and a second storage area with a capacity RxLL such that the lengths of the strings can be varied by adjusting the multiplier R to suit the equipment available for merging the strings. The first LL records of an unsorted sequence are entered into the first store; a comparison is then made between the record in the store having the lowest sort key and the subsequent records in the sequence. Each time the comparison is made, if the subsequent record is higher it replaces the lowest record in the first store and this lowest record is appended to an output string; if however the subsequent record is lower it is placed in the second store. When the second store is full (i.e. it contains RxLL records) the output string is completed by adding to it, in sequence, the LL records remaining in the first store and a new output string is started. The first LL records from the second store are entered into the first store and the comparison made as before with each of the records left in the second store and then with those in the unsorted sequence. As before lower records are returned to the second store and when it is again full the second string is completed. This is repeated until all the input records have been allocated to output strings which are then merged in known manner. The first storage area is in primary storage while the second storage area and the stored strings are in secondary storage. The method is useful in a time sharing computer since the lengths of the output strings are not limited by the size of primary storage available.