Page "Virtual Storage Access Method" Paragraph 9
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Wikipedia
When records are inserted into a control interval, they are placed in the correct order relative to other records.
This may require that records have to be moved up the control interval.
Conversely, when a record is deleted, later records are moved down so that the free space remains contiguous.
If there is not enough free space in a control interval for a record to be inserted, the control interval is split.
Roughly half the records are stored in the original control interval while the remaining records are moved into a new control interval.
The new control interval is taken from a pool of free control intervals within the same control area as the original control interval.
If there is no remaining free control interval within that control area, the control area itself is split and the control intervals are distributed equally between the old and the new control areas.
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