Abstract: With respect to input/output requests; a microprogram controls collection of data according to the data format; data accessing divides the requests for every recording medium and performs asynchronous processing; an on-line process is carried out in view of the processing priority order of the requests; parallel accessing sets requests for each medium; buffer control assures a block buffer and a page address list before receiving requests; data accessing sets a list of CCHHR codes in response to a continuous characteristic of the stored state in the recording medium; and mode deciding judges the two data transfer modes, a page search mode and a data search mode, in response to the requests.

Abstract: A controller with a buffer is provided between a main memory and an external storage. This controller supplies a given request for access to the external storage and issues a preload request for a retrieval extent of the next access request by the time when data associated with this first access request is completely transferred to the buffer memory or to the main memory. Moreover, the controller stores the preloaded data in the buffer and, for the next access request, it transfers the data stored in the buffer to the main memory. Therefore, even when the host side (CPU) is processing, the access to the external storage can be made simultaneously, thus the response time and the operating ratio of the computer system being improved.

Abstract: A set of sorted columns of one table stored in a DB machine are binary-searched by a hardware in synchronism with data transfer when another table is read from a disk unit, to select a row to be joined. Where a key word sequence to be searched is stored in ascending or descending order, determination of a maximum address in an area in which key words smaller than a search key are stored and determination of a maximum address in an area in which the key words smaller than or equal to the search key are stored are parallelly executed to determine the store range in one searching.

Abstract: A skip table is prepared from which a state of a subsequent symbol string and an address of one or plural symbols to be subsequently inputted can be readily determined by making reference to a set of a current symbol string search state and one or plural symbols to be subsequently inputted of the symbol string. When executing searching for the symbol string, data stored in the skip table are looked up to assure the symbol string search by inputting only a minimized number of necessary characters of the symbol string. Necessity of inputting all the characters of the symbol string for searching is eliminated and the processing speed can be increased considerably. A plurality of symbol strings may be searched for.