Example: Record format *VS

This is an example of record format *VS, which consists of graphics with explanations.

Variable-length, deblocked, spanned (*VS).

Figure 1. Variable-length, deblocked, spanned (*VS)
This graphic depicts three
blocks, with all three in a flowing order. Block 1 consists of XX YY, VV WW,
and 1st segment of Record A. Block 2 consists of XX YY, VV WW, and Middle
segment of Record A. Block 3 is made up of XX YY, VV WW and the Last segment
of Record A.

This graphic depicts three
blocks, with all three in a flowing order. Block 1 consists of XX YY, VV WW,
and 1st segment of Record A. Block 2 consists of XX YY, VV WW, and Middle
segment of Record A. Block 3 is made up of XX YY, VV WW and the Last segment
of Record A.

XX and YY make up the BDW for each data block. XX is the length of all records in each block plus the length of the BDW (4 bytes). YY represents currently reserved fields and must be 00. XX should be the actual length of the data block that is written.

Note that logical record A spans over three actual data blocks on the tape.

By breaking down each piece of record A, you can see that each segment has its own characteristics.

Figure 2. Segments of record A
In this diagram, the first
segment of Record A is TT CC and the 1st part of Record A data. The second
segment of Record A is TT CC and the middle part of Record A data. The last
segment of Record A is TT CC and the last part of Record A data.

In this diagram, the first
segment of Record A is TT CC and the 1st part of Record A data. The second
segment of Record A is TT CC and the middle part of Record A data. The last
segment of Record A is TT CC and the last part of Record A data.

Note that the actual mapping of the entire block 3 is shown in the following figure:

Figure 3. Mapping of block 3
This diagram shows block
3, which contains 4 parts. From left to right is XX YY, VV WW, TT CC, and
the last part of Record A.

Each segment of record A has its own by mapping by including the SDW. TT and CC make up the SDW. TT is the length of the record plus the length of the SDW (4 bytes). CC is the segment control character. The first byte of the CC defines which part of the record the segment is. The values of the control character can be:

00 binary - Complete logical record
01 binary - First segment of a multi-segment record
10 binary - Last segment of a multi-segment record
11 binary - Middle segment of a multi-segment record

The second byte of the control character is reserved, and should be 0. TT should be the actual length of record data segment plus the length of the SDW (4 bytes).

From a user's point of view, a logical view of record A is the same as other records defined above.

Figure 4. Logical view of record A
This record is comprised
of VV WW and the 1st, middle, and last portions of Record A data, concatenated.