IBM 4381 Manual page 65

Data Streaming Mode
Data streaming mode of operation is standard for all the block multiplexer channels
present in a 4381 Processor. Data streaming mode enables certain 4381 block
multiplexer channels to handle faster data rates and all 4381 block multiplexer
channels to handle a longer channel-to-control-unit cable length. Specifically, a
maximum channel-to-control-unit cable length of approximately 122 meters (400
feet) is supported for control units that are capable of operating in streaming mode
and a data rate of up to 3 Mb/sec can be achieved for this cable length for
channels 1 through 4 in uniprocessor 4381 model groups.
When a block multiplexer channel is capable of data streaming, both data
streaming and nonstreaming control units can be attached to the block multiplexer
channel. Control units that are capable of streaming must be set by the customer
engineer to operate in streaming or nonstreaming mode for each
1/0
interface to
which they are attached. In addition, control units set to operate in streaming
mode must be allocated UCWs (for System/370 mode of operation) that are
assigned streaming mode. Nonstreaming control units connected to a channel that
is capable of streaming are still subject to their normal maximum
channel-to-channel -unit cable length and operate at their usual rated speed.
The following can be set to operate in data streaming mode:
• 3880 Storage Control (all models)
3848 Cryptographic Unit with the appropriate EC installed
• 3838 Array Processor with the optional Data Streaming feature installed (to
permit operation at 3 Mb/sec)
• 3088 Multisystem Channel Control Unit
For a 3880 unit, the use of streaming or nonstreaming mode is set for each channel
to which the two storage directors are attached. Thus, when no channel-switching
feature is installed, a storage director always operates in the mode, streaming or
nonstreaming, set for the channel to which it is connected. When channel
switching is installed the mode of operation, streaming or nonstreaming, is set for
each channel to which the storage director is attached, and the storage director can
operate in streaming mode for some channels and nonstreaming mode for others, if
necessary.
For a 3380 Model 1 or 2 with 3330-series, 3340/3344, 3350, 3370, or 3375 drives
attached, each storage director can be set to operate in streaming or nonstreaming
mode. The maximum channel-to-control-unit cable length for a 3880 Model 1 or 2
with 3330-series, 3340/3344, or 3350 drives attached is 122 meters (400 feet) for
both streaming and nonstreaming mode of 3880 operation when the 3380 is
attached to a 4381 Processor.
The maximum channel-to-control unit cable length for a 3880 Model 1, 2, or 4
with 3370 or 3375 drives attached is 61 meters (200 feet) for nonstreaming mode
and 122 meters (400 feet) for streaming mode of 3880 operation when the 3880 is
attached to a 4381 Processor.
A 3880 Model 2 or 3 storage director with 3380 devices attached must be attached
to channel with a 3 Mb/sec data rate in a 4381 Processor and operate in data
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A Guide to the IBM 4381 Processor
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