On Thu, Jan 17, 2008 at 11:26 AM, in message <[EMAIL PROTECTED]>, Clark Morris <[EMAIL PROTECTED]> wrote: >VSAM is already FBA Sort of. A VSAM file, once loaded, consists of blocks of all the same size, but VSAM allows more than one block size (e.g., 4K and 8K). FBA, to me, means that all blocks are always the same size. In a message dated 1/17/2008 6:47:55 P.M. Central Standard Time, [EMAIL PROTECTED] writes: >FBA is what the media is. All of IBM's "CKD" devices have in one sense already been FBA for several decades. Each new device has not necessarily had the same block size, however. The block size I am talking about here is the size of the segment of consecutive bytes that the controller allocates whenever any new piece of data is to be written onto a track. E.g., if you try to write a record with a one-byte-long data field onto a 3390, the controller uses an entire segment, consisting of around thirty bytes (31? 32? 37?) to hold the one byte in the data field. These extra bytes are in addition to the gaps in between records and pieces of records on the track. Whenever a skip displacement has to be assigned, the size of the area to be skipped is always an integral number of these segments. The two FBA devices that IBM allowed to be used by VM and VSE, the 3310 and 3370, have physical block sizes of 512 bytes. At least the software must assume so. But what the controller really writes onto a 3310 and 3370 track may be something different, as it is for a 3390. Bill Fairchild Franklin, TN
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