分时总线、交叉开关和多端口存储器的区别——互连结构

先决条件：详细学习分时总线、交叉开关和多端口存储器互连结构。

介绍 ：
互连结构可以决定整个系统在多处理器环境中的性能。在多处理器系统中，处理器必须能够共享一组主内存模块和 I/O 设备。这种共享能力可以通过互连结构提供。常用的互连结构如下：

1. 分时/公共巴士(之前讨论过)
2. 横杆开关
3. 多端口存储器
4. 多级交换网络(前面讨论过)

5. 超立方体系统

分时/公共巴士：
在多处理器系统中，分时总线互连提供连接所有功能单元的公共通信路径。

多处理器系统中的分时/公共总线

横杆开关：
如果公共总线系统中的总线数量增加，则到达每个内存模块都有可用的单独路径的点。 Crossbar Switch(用于多处理器)为每个模块提供单独的路径。

交叉开关

多端口内存：
在多端口存储器系统中，控制、交换和优先级仲裁逻辑分布在整个交叉开关矩阵中，该矩阵分布在存储器模块的接口处。

多端口存储器

时间共享总线、交叉开关和多端口存储器之间的区别：

	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.