Difference between Time Shared Bus, Crossbar Switch & Multiport Memory – Interconnection structure
Interconnection structure can decide the overall system’s performance in a multi-processor environment. The processors must be able to share a set of main memory modules & I/O devices in a multiprocessor system. This sharing capability can be provided through interconnection structures. The interconnection structure that are commonly used can be given as follows :
- Time shared / Common Bus (Discussed earlier)
- Cross bar Switch
- Multiport Memory
- Multistage Switching Network (Discussed earlier)
Time shared / Common Bus :
In a multiprocessor system, the time shared bus interconnection provides a common communication path connecting all of the functional units.
Cross bar Switch :
A point is reached at which there is a separate path available for each memory module, if the number of buses in common bus system is increased. Crossbar Switch (for multiprocessors) provides a separate path for each module.
Multiport Memory :
In Multiport Memory systems, the control, switching & priority arbitration logic are distributed throughout the crossbar switch matrix which is distributed at the interfaces to the memory modules.
Difference between Time Shared Bus, Crossbar Switch & Multiport Memory :
|Time Shared Bus||Crossbar Switch||Multiport Memory|
|1.||Lowest cost for hardware & least complex.||Cost-effective for multiprocessors only as a basic switching matrix is required (to assemble functional units.)||As most of the control & switching circuitry is in the memory unit, it is expensive.|
|2.||System Expansion will degrade performance.||System Expansion can improve performance.||It is difficult to expand the system(design).|
|3.||Overall, system capacity limits the transfer rate & if the bus fails, the whole system will fail.||Transfer rate is high but more complex.||Potential for a very high total transfer rate.|
|4.||Modifying the hardware system configuration is easy.||Limited expansion of system, only by size of switch matrix.||Lots of cables & connectors are required.|
|5.||We cannot have transfers from all memory modules simultaneously.||We can have transfers from all memory modules simultaneously.||We can have transfers from all memory modules simultaneously.|
|6.||Lowest Efficiency & suitable for smaller systems only.||Functional Units are the simplest & cheapest.||Functional units permit low-cost-uniprocessor.|