The BLOB files that are part of a logical table in DBISAM are based upon a default block size of 512 bytes. However, this block size may be changed when creating a new table and at any time by simply altering the structure of a table. The valid block sizes are 64 bytes to 64 kilobytes. Because the block sizes are fixed, it is very well possible to have slack space in the blocks. For example, a memo field that contains 400 bytes will consume 512 bytes on disk if the block size were left at the default of 512 bytes. The ideal blob block size that minimizes the amount of slack space is essentially an average of the sizes of all of the blob fields for the table.