88 Part 1½ Fundamentals Section 2 ½ The Computer Space
7 K-trunk, concurrency K. The trunk structure can be viewed as a higher-concurrency version of switch 4 or a reduced-cost version of switch 5. A noncomputer example of a trunk switch is the telephone exchange.
9 Cross-point. Analogous to switch 5.
10 K-trunk. Analogous to switch 7.
Processor-Memory Switching
With the advent of multiple processors, memory-processor switching became an important problem. The Mp-P switch is what makes multiple processors possible, and it is a determining factor in both performance and reliability.
The structure of the processor-memory switch for computers that have
multiple memories and multiple processors is a lattice if simultaneous
memory-processor dialogues are allowed. A cross-point switch provides redundancy
and is used to form the lattice structure. To vary from the full-duplex/duplex
switch (for m memories and one processor, or p processors
and one memory) requires more components to be devoted to the switching,
to buffering, and to arbitration control (see Chap. 22). Hence duplex switches
are used on most multiprocessor computers. The processor-memory switching
possibilities can be seen nicely in Fig. 19. The important switch parameters
are the number of memories, the number of processors, and the number of
simultaneous processor-memory dialogues. In current designs P always originates
the dialogue, which is generally taken to mean the