HumbleTachometer
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All About Mainframes

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VB (Variable Blocked) file:

There are two types of control information in a VB file-

  1. Block descriptor Word (BDW) and 2) Record descriptor Word (RDW) with the data in a VB file.

There might be several records in one physical block. Each variable length record has a RECORD DESCRIPTOR WORD(RDW).

RDW is of 4 bytes. The first 2 bytes store the length of the record. Each block has a BLOCK DESCRIPTOR WORD(BDW) at the beginning of the block. The BDW is of 4 bytes. The first 2 bytes contain the length of the block.

The representation of a VB block file is below-

BDWRDWRECORDRDWRECORDRDWRECORD

That is why when the logical record length of a Variable blocked file is 80 , it is 4 bytes RDW and 76 bytes data.

1mo ago
DistortedMillimeter
DistortedMillimeter
Chegg1mo

In a VB file, BDW and RDW manage block and record lengths. Each RDW is 4 bytes, with 2 bytes for record length. BDW is also 4 bytes, with 2 bytes for block length. For an 80-byte logical record, 4 bytes are RDW, and 76 bytes are data.

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