| 摘要 |
PURPOSE:To shorten a searching time and to reduce the conversion into scraps with a hierarchical bit map by controlling the idle state with plural pairs of bits defined as a unit. CONSTITUTION:For the bit map 21 of level 0, the bits (x01-x0n) have the 1:1 correspondence to the areas (y1-yn) of fixed sizes forming an external memory 1 respectively with a bit defined as a unit. The bit values (0)2 and (1)2 means the presence and absence of an idle area respectively. The bit maps 22 and 23 of levels 1 and 2 define two bits as a unit and each of bits (x11-x1m and x21-x2l) corresponds to two units of the bit map of a level lower by 1 step. Then the bit values (00)2, (01)2, (10)2 and (11)2 mean that all areas are idle, an idle area exists at a level lower by 1 step, an idle area exists at a level lower by 2 steps and all areas are busy respectively.
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