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:
- 分时/公共巴士(之前讨论过)
- 横杆开关
- 多端口存储器
- 多级交换网络(前面讨论过)
-
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。
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。
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。
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. |