GB1289451A - - Google Patents

Abstract

1289451 Sorting data words represented by electrical signals NATIONAL CASH REGISTER CO 3 May 1971 [4 May 1970] 12642/71 Heading G4M In a sort operation, e.g. with regard to payroll records, a block of data, e.g. of 20 words has a key word such as the employee number which is used to arrange the records in order such as ascending order of employee number. A processor 20 allocates a portion of a main memory 10 into a work area 11, a parameters file 13 and an output buffer or string list area 12. Records, e.g. from punched cards are read into the work area 11 until the area is full. In the parameter file is stored the initial address Bo of the first record in area 11, the address of the final record, the length of the key word, the location Go of the first key word, the initial address Po of area 12, the final address Pin of area 12 and the length, e.g. 20 words of each record. A command is sent to a sort processor 30 which contains a micro-programme store. The command has a function code indicating the nature of the sort operation and an address Ao defining the intial location of the parameter file. Data from the parameter file is stored in a register file 42 of the sort processor 30 and successive key words are read from the main memory 10 and stored in a search memory 35. The search memory may be a recirculating memory formed of MOS dynamic shift registers or may be an associative memory with LSI components, and has a section storing a key word and a section storing the address Bo to Bu of its associated record. The key words are found by incrementing address Go with the number of words in the record. When memory 35 is full the micro-programme store 45 commences an operation fetch the next lowest Key word. A key word is read into a register 38 and transferred to register 40 while a further word enters register 38. The words are compared using comparator 39b and the lowest word is transferred to or remains in register 40 while another word is entered and compared and the process continues until all words have been compared. The address Bo of the lowest key word is then stored at address Po of area 12 and the keyword is stored in register 38. The word in register 38 is incremented by 1 and the words in store 35 are searched for equality using comparator 39a. The key word is successively i ncremented until equality occurs wherein the new word is used as a base word in register 38 and its address Bo-Bu is stored in address Pi of area 12. The process is continued until area 12 is full. The list in area 12 is used to store records from area 11 in ascending order of the employee number on magnetic tape and more records may then be read in and sorted. Several resulting strings of data may then be sorted and merged.