PURPOSE:To improve the using efficiency of a physical segment by dividing the physical segment constituting a main storage device into plural logical segments with fixed length and assigning the logical segments to a sub-program. CONSTITUTION:A logical segment management table 22 for dividing a physical segment 30 into plural logical segments 31 with fixed length and managing respective logical segments 31 is prepared. In the case of registering a sub-program 40, areas with a small size are assigned to the segments 31 by a segment size judging means 11, a logical segments acquiring means 12 and a logical segment registering means 13. In the case of deleting the contents of the sub-program 40, logical segments 31 having been not used are deleted by a logical segment retrieving means 14 and a logical segment deleting means 15.
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