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rajesh_mbt
New User
Joined: 27 Mar 2006
Posts: 97
Location: India
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| Can any one clarify why we need to add 4 bytes with actual length for variable block file during submission of jcl? |
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enrico-sorichetti
Superior Member
Joined: 14 Mar 2007
Posts: 10873
Location: italy
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how else would tell the block and record lengths
he VB layout is...
four bytes for the BDW bock descripotor word
followed by N tuples of
four bytes for the RDW record description word
the data itself
but anyway the practical reason is ... the manual says so |
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Garry Carroll
Senior Member
Joined: 08 May 2006
Posts: 1193
Location: Dublin, Ireland
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The 4bytes contain the RDW (record descriptor word) which contains each individual record's length. Similarly, an additional 4 bytes are used to contain the size of the block containing the variable records.
Garry. |
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Anuj Dhawan
Superior Member
Joined: 22 Apr 2006
Posts: 6250
Location: Mumbai, India
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Hi,
A variable-length logical record consists of a 4-byte record descriptor word (RDW) followed by the data. The first 2 bytes contain the length of the logical record. The last 2 bytes must be 0 because these are used for spanned records. When using variable-length records on output, you must provide the RDW; for input, the operating system provides the RDW.
Click here, this link would give you a pictorial representation of what goes behind. |
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Aaru
Senior Member
Joined: 03 Jul 2007
Posts: 1287
Location: Chennai, India
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| Quote: |
| The first 2 bytes contain the length of the logical record. The last 2 bytes must be 0 because these are used for spanned records. |
Adding to what Anuj had posted, last 2 bytes are populated with hexadecimal Zeroes. |
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