GB1534290A - Computer system with data base instructions - Google Patents

Abstract

1534290 Data processing HONEYWELL INFORMATION SYSTEMS Inc 23 Dec 1975 [23 Dec 1974] 52581/75 Heading G4A Data is recorded in the form of sets of records each set having an owner record and at least one member record, each record forming one line of a page, Fig. 16a, and including a pointer sequence providing pointers to one or more records of the set. Each page includes a table 1602 correlating line numbers of records and their offsets within the page. The pointer sequence of a member record may include pointers to the next record, the previous record and the owner record of the set (Fig. 15c, not shown) whereas the pointer sequence of an owner record may include pointers to the first and last member records of the set (Fig. 15d, not shown). Each page is addressed by a page descriptor (Fig. 16b, not shown) providing the respective area (file) and page numbers and pointers to the previous and following descriptors in a chain of the page descriptors relating to the pages in main memory. When a page is requested a control pointer (Fig. 16c, not shown) is an extension to a system base 1215, Fig. 12, provides a G-number which is the number of a segment pointed to by an entry in a G-table 1212 and a displacement within that segment at which is the beginning of the chain of page descriptors. The chain of page descriptors is then searched to determine whether the requested page is in the main memory or the backing store; an address in the form of segment and address within the segment is then generated. Each page, Fig. 16a, includes a page header 1601 describing the length of the page and the number of records in the page and, for each record, an offset 1603 and a two-bit field 0 which indicates whether the record is inactive, logically deleted (it contains no information but occupies memory space), physically deleted or active. Records may be virtual memory records, used for internal operating procedures, and including pointers to addresses in the form of segments and address within the segment, or data base records, generally used by user programs, and including pointers to addresses in the form of area, page, line. Set and record descriptors (Figs. 18a, 18b, not shown) describe the properties of a given set and record respectively. The system base 1215, Fig. 12, accessed by a base address register 1202, provides the base addresses of G-table 1212 and a J-table 1204 and the job step (J) number of the currently operating process which accesses a J-table entry 1217 which provides the base address of a P- table 1205. The process group (P) number of the currently operating process from system base 1215 accesses, 1217, from the P-table the address of the process control block 1206 of the currently operating process which acts as a temporary storage area for information necessary to start or restart that process. One of two address space words ASW0 or ASW1 in the process control block 1206 is selected by part of the contents of a base register 1201 and points to a segment table word array 1207 or 1208 which together with base register 1201, selects a segment table 1209 or 1210; a segment descriptor is then derived from the segment table as addressed by part of the contents of base register 1201 and accesses a user segment 1211. The system base 1215 also provides an internal processor queue word which points to the head of a queue of processes waiting for resources, 1213, in the GO segment pointed to by the zero G-number in G-table 1212; such processes are queued on semaphores, queues of resources waiting for processes and free semaphores also being provided in the GO segment (Fig. 9, not shown).