Basic Uniprocessor architecture:
A typical uniprocessor architecture consists of three major components: the main memory, the Central Processing Unit (CPU) and the Input/Output subsystem.
We identify parallel processing mechanisms in the following six categories:
- Multiple functional units:
Many of the functions of the ALU can be distributed to multiple functional units which can operate in parallel. - Parallelism and pipelining with the CPU:
Parallel adders using carry-save and carry-lookahead instead of the bit-serial adder. The use of multiple functional units is a form of parallelism within the CPU.
Various phases of Instruction execution are now pipelined using Instruction prefetch and data buffering techniques. - Overlapped CPU and I/O operations:
I/O operations can be performed simultaneously by using separate I/O controllers, channels or I/O processor. DMA(direct-memory-access) to provide direct information transfer between main memory and I/O devices. - Use of hierarchy memory systems
A hierarchical memory system can help in speeding up memory access.
- Balancing of subsystem BandWidths
As CPU is fastest with processor cycle tp of tens of nanoseconds, the main memory has cycle time tm of 100s of nanoseconds and I/O devices with average access time td of few milliseconds.td>tm>tpBandwith of a system is no. of operations performed per unit time. Let W be no. of words delivered per unit time, then B=W/t.
So, the speed gap between CPU and memory can be closed up by using fast cache memory in between them.
I/O channels with different speeds can be used between the slow I/O devices and memory to speed up. - Multi Programming and Timesharing
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