ENVS 1200 Lecture Notes - Lecture 8: Opcode, Ieee 1394
13 May 2018
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ENVS 1200 Lecture 8 Notes – Blurring the Line
Introduction
• Sense (used to determine the status of a device)
• Transfer in channel (equivalent to a JUMP instruction)
• Although these instructions are used specifically for I/O, in other respects they are
similar to other computer instructions.
• Each instruction has its own op code and address field.
• Each instruction results in the execution of a fetch-execute cycle by the channel
subsystem.
• A simple channel program appears
• This program performs a disk read operation.
• The channel control word instructions are designed in such a way that a single I/O
operation can transfer a number of blocks.
• The blocks do not have to be contiguous on the disk or tape, nor do they have to be
contiguous in memory.
• This feature provides a lot of flexibility.
• Physically, the channel subsystem is connected to the CPU by a bus, and the various
control units and I/O devices are also connected by buses.
• Conceptually, the channel architecture is very different
• However, and the buses connecting the various parts of the I/O system are not
identified as such.
• It is worth observing that there has been a recent significant blurring of the line that
distinguishes between I/O buses, I/O channels, and networks.
• PCI-Express, USB and FireWire are all examples of recent I/O buses that have many of
the characteristics of networks.
• PCI-Express uses a switch similar to that found in Ethernet networks to connect lanes
together.
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