PURPOSE: To utilize the main storage of a virtual storage type computer system effectively by specifying the maximum number of pages which can be loaded on batch basis for every work set frame.

CONSTITUTION: When page absence occurs in program execution, the control block WSCB of the working set WS frame of a segment descriptor specified by the identifier of the WS frame is read out to obtain the maximum number MXPN of pages. The obtained maximum number MXPN of pages is compared with the last obtained number of pages to use the smaller value as a necessary page. When the number of pages of a segment is smaller than MXPN, all pages in the segment are regarded as pages to be loaded on batch basis. When the MXPN is larger, pages from right before the page absence to the MXPN in precedent page order are regarded as pages to be loaded on batch basis after progress from the page where the page absence occurs to the last page of the following page segment is made.