30:20 Support Processor Subsystem; 30:25 Channels; General Description - IBM 4381 Manual

Operation of the entire high-speed buffer for an instruction processing function
cannot be disabled in a 4381 Processor. However, utilization of an individual
buffer block can be disabled by turning on the malfunctioning bit in the associated
directory entry, as is done when reconfiguration is not possible.
30:20 Support Processor Subsystem
Components and Functions
30:25 Channels
General Description
The support processor subsystem provides basic operational functions for 4381
Processors and is the primary maintenance tool for diagnosing hardware
malfunctions. It is designed to maximize total system availability and to provide
rapid fault location and repair, where possible.
The components of the support processor subsystem are the support processor,
support bus adapter, local channel adapter, console attachment adapter and
attached devices, power adapter, power information panel, common
communications adapter for the Remote Support Facility, and two system diskette
drives and associated adapters.
The support processor subsystem in 4381 Model Groups 14 and 3 is functionally
like that in uniprocessor 4381 model groups as described in Section 20: 15.
Note that in a 4381 Model Group 14 or 3 Processor, the natively attached primary
console and up to three additional displays and/ or printers attach only to byte
multiplexer channel 0 for instruction processing function 0 via the local channel
adapter. Thus, if a malfunction prevents operation of instruction processing
function 0, the 4381 cannot be used in uniprocessor mode with only instruction
processing function l operating unless an alternate console is connected to a
channel in the group for instruction processing function 1.
The 4381 Processors implement advanced channel functions like those
implemented in 4341 Processors, such as block multiplexing and data streaming,
and also offer more channels and higher aggregate channel data rates than do 4341
Processors.
Two standard channel groups, one for each instruction processing function, are
provided for 4381 Model Group 14 and 3 Processors. Each standard channel
group consists of one byte multiplexer channel, addressed as channel 0, and five
block multiplexer channels, addressed as channels 1 through 5, providing twelve
standard channels in the configuration. Channel 5 in each channel group can be
configured as a byte, instead of a block, multiplexer channel.
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A Guide to the IBM 4 3 81 Processor