Microsoft Knowledge Base

Microsoft File uses disk space in the following manner:

If the new field is not of fixed length, such as a text field, no space is initially added to each existing record for that field. When information is added to that field in new or existing records, the field takes up disk space. A fixed-length field, such as a date field, does not immediately take up space on the disk, but space is allocated for it in new records and updated records even if no information has been entered in that field.

When data is added to a record and the record no longer fits in its allotted disk space, File searches the existing data file for enough free space to move the record to. Free space within the data file is created by deleting information. If there is not enough free space in the data file, the record is moved to the end of the data file.

When you choose Save Records As from the File menu, all records are updated. If you have added a fixed-length field, space is allocated in all records for the field. Also, all areas within the data file that were unused are closed up in the new file.