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Tape Blocking<br />
Chapter 2. Magnetic Tape Formats<br />
Tape Blocking<br />
When written to tape, the job file consists of variable-length records that<br />
are grouped into variable-length blocks. Each block on the tape starts with<br />
a 2-byte block-length field. This binary field indicates the length of the<br />
block, in bytes, including the block length field. The first byte in the block<br />
length field is the most significant byte and the most significant bit in each<br />
byte is the hex 80 bit. For example, hex 09 B6 specifies a block length of<br />
2,486 bytes.<br />
The maximum block length is 4,096 bytes. Each block must contain an<br />
integral number of records. Records cannot be divided between blocks<br />
(spanned).<br />
For job files that contain data for multiple RIPs, each block can contain<br />
data for only one RIP. A RIP command, identifying a specific RIP, must be<br />
the first record in each block after the first block. Multiple RIPs are<br />
explained in Chapter 1.<br />
Reference Guide 2 - 5
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