Example: Record format *VS
Here is an example of record format *VS.
Variable-length, deblocked, spanned (*VS). Figure 1. Variable-length, deblocked, spanned (*VS)
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
Note that the actual mapping of the entire block 3 is shown in the following figure: Figure 3. Mapping of block 3
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
