December 2006
Intermediate to advanced
228 pages
6h 20m
English
book
Introduction to the New Mainframe: Large-Scale Commercial Computing
by Mike Ebbers, Pilar Gonzalez Adrados, Frank Byrne, Rodney Martin, Jon Veilleux
Content preview from Introduction to the New Mainframe: Large-Scale Commercial Computing
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112 Introduction to the New Mainframe: Large-Scale Commercial Computing
6.3 Control units
The channel design requires devices to be connected to a control unit.
The function from a control unit is to execute channel commands. The channel
protocol consists of channel command words (CCWs), which represent actions
that the device has to perform. An operation can consist of more than one CCW,
referred to as a
chain. The control unit is responsible for making sure that an
operation is complete before requesting the next CCW in the chain from the
channel.
For example, adding data to the end of an existing file on tape requires the
following operations:
1. Position the tape at the end of the existing data
2. Write the new data
3. Indicate that the writing ...
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