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To: Glenn Perry who wrote (3896)	11/25/1998 2:26:00 PM
From: Brian D. Potts	Read Replies (1) \| Respond to of 17679

I'll attempt to decipher it. It sound very similar to the methods of storing information on mainframe direct access storage devices (DASD). The block size is the minimum that can be written or read at any given point in time. It sounds like this is a fixed value (1,199,840 bytes) on the DST drive. The most efficient use of this space would be to break up data ("records") into pieces that are multiples of 1,199,840. For instance , if the data (record) is 160 bytes then you could fit exactly 7,499 records in a block. However if the record was 159 bytes long you would be able to fit 7546 records in a block but would waste 26 bytes in every block that could never be used (7546 * 159 + 26 = 1,199,840). The "software" takes care of breaking the physical block up into the useable record size and vice versa. Finally, if you don't have a fixed data size you may use a variable length "record". It looks like DST does this by specifying a block size of 1 byte. Most likely this is somewhat misleading because the "software" must somehow determine where the end of a record (data block) occurs. It usually does this by adding on a unique string of characters that signifies the end of the record. This end of record indicator also wastes space by adding bytes to each record. What does this all mean? With the amount of storage available on a DST drive, not much. What they're basically saying is the drive and it's software will handle all of this for you. However, this information can be used to optimize the use of the tape and the DST drive. Brian