GB1444228A - Data structure processor - Google Patents

Abstract

1444228 Data processing NATIONAL RESEARCH DEVELOPMENT CORP 18 Sept 1973 [3 Oct 1972] 45494/72 Heading G4A A data processing system includes an addressable primary store and an address translator including address storage means and arranged in response to an applied address to provide an associated, translated address to the primary store, the address translator being arranged to change the association between applied and translated addresses without the transfer to the address storage means of further addresses. A sixteen word primary store 13 is addressed by four bits from register 19 via translator 14. The translator, Fig. 2a, includes four groups E-H each of two single bit registers, and operates only on the two most significant bits of the address to address one of four groups A-E of words, each group containing four words. The two most significant bits are applied to a decoder which produces one out of four outputs α 0 -α 3 to gate via gates 27-34, the contents of the corresponding group of registers to the address inputs of store 13. Further gates 35-42, and 51-66 together with two groups K, L of buffer registers are provided to exchange the contents of pairs of groups of the registers E 2 - H 3 whereby the association between an address applied to the decoder and the address supplied by the translator is changed. Further address modification is provided by exclusive-ORing, at 18, a flag bit (1 or 0) with the address in register 19 to provide a modified address which is then supplied to the translator as above. Assuming block A in store 13 is addressed with an address whose two most significant bits are 0, 0 and block B by an address 0, 1, then by exclusive-ORing a flag 1 with the second address bit an applied address 0, 0 produces an address 0, 1, and an applied address 0, 1, an address 0, 0. Thus blocks A and B are effectively interchanged. A similar modification, at 17, may be performed on the least significant address bit to effectively exchange words within a group. The arrangement is said to be of use in a data processing system providing a graphical output, e.g. on a CRT. The arrangement is also of use when processing mathematical expressions in that it enables a parameter in the expressions to be changed without necessarily requiring the whole expression to be recalculated. This is achieved using so called "plexes" which are groups of four words defining an operand or an operator. The plexes are stored in respective groups of words A-C in store 13 and the system is arranged to operate on operands stored in plexes in groups A and B in accordance with an operator in a plex stored in group C. Exemplary programs are described for calculating, for adding entries to and removing entries from a list, each plex in the list referring to the next, and using circular lists; address modification being used to effectively "move" plexes within store 13 without actually having to physically move data.