2.3: The Multicore and Multiprocessor Segments

Introduction

This section introduces the learner to the multicore and multiprocessor. It also highlights why computer architecture is moving towards multiprocessor architecture

Activity details

Central Processing Unit is what is typically referred to as a processor. A processor contains many discrete parts within it, such as one or more memory caches for instructions and data, instruction decoders, and various types of execution units for performing arithmetic or logical operations.

Multicore: is a type of architecture where a single physical processor contains the core logic of two or more processors.

A multicore CPU has multiple execution cores on one CPU. This can mean different things depending on the exact architecture, but it basically means that a certain subset of the CPU’s components is duplicated, so that multiple “cores” can work in parallel on separate operations.

This is called CMP, Chip-level Multiprocessing.

A multiprocessor system contains more than one such CPU, allowing them to work in parallel. This is called SMP, or Simultaneous Multiprocessing. That is Multi-processing simply means

putting multiple processors in one system.

For example, a multicore processor may have a separate L1 cache and execution unit for each core, while it has a shared L2 cache for the entire processor. That means that while the processor has one big pool of slower cache, it has separate fast memory and arithmetic/logic units for each of several cores. This would allow each core to perform operations at the same time as the others.

Single-core CPU Chip

Figure 1 below illustrates the single-core CPU chip. it has the components register files, ALU, bus interface and the system bus. The figure also shows the single core clearly marked out

Figure 1

Multi-core architectures

The cores fit on a single processor socket, also called CMP (Chip Multi-Processor)

Multicore System:

A Multicore system usually refers to a multiprocessor system that has all its processors on the same chip. It could also refer to a system where the processors are on different chips but use the same package (i.e., a multichip module). Multicore systems were developed primarily to enhance the system performance while limiting its power consumption. It consists of

1. General - purpose programmable cores,

2. Special - purpose accelerator cores,

3. Shared memory modules,

4. NoC (interconnection network), and

5. I/O interface.

Figure 2 below illustrates the Multi-core CPU chip

Figure 2

In Figure 2 all processors are on the same chip. The Multi-core processors are MIMD, i.e. different cores execute different threads (Multiple Instructions), operating on different parts of memory (Multiple Data). Also Multi-core is a shared memory multiprocessor, i.e. all cores share the same memory

NB

The main reason for which computer architecture is moving towards multicore systems is scalability. That is, as we increase the number of processors to enhance performance, multicore systems allow limiting power consumption and interprocessor communication overhead. A Multicore system can be scaled by adding more CPU cores and adjusting the interconnection network. More system programming work has to be done to be able to utilize the increased resources. It is one thing to increase the number of CPU resources. It is another to be able to schedule all of them to do useful tasks.

Multiprocessor

Multiprocessor. is the use of two or more central processing units (CPUs) within a single computer system.

Multiprocessor System

A multiprocessor system has its processors residing in separate chips and processors are interconnected by a backplane bus. Multiprocessor systems were developed to enhance the system performance with little regard to power consumption. A multiprocessor system has good performance and its constituent processors are high - performing processors.

Main Differences between Multicore Systems and Multiprocessor Systems:

The differences are as expressed in Table 4

Table 4

	Multiprocessor system	Multicore system
Integration level	Each processor in a chip	All processors on the same chip
Processor performance	High	Low
System performance	Very high	High
Processor power consumption	High	Low
Total power consumption	Relatively high	Relatively low

Conclusion

This section introduced the main reason why computer architecture is moving towards multicore systems which is scalability. It enables an increase in the number of processors.

This has enhanced performance, multicore systems allow limiting power consumption and interprocessor communication overhead

Assessment

Distinguish the multicore and multiprocessor architectures

A CPU, or Central Processing Unit, is what is typically referred to as a processor. A processor contains many discrete parts within it, such as one or more memory caches for instructions and data, instruction decoders, and various types of execution units for performing arithmetic or logical operations.

A multiprocessor system contains more than one such CPU, allowing them to work in parallel. This is called SMP, or Simultaneous Multiprocessing.

A multicore CPU has multiple execution cores on one CPU. Now, this can mean different things depending on the exact architecture, but it basically means that a certain subset of the CPU’s components is duplicated, so that multiple “cores” can work in parallel on separate operations.

This is called CMP, Chip-level Multiprocessing.