Multi-core processors have multiple processing units (cores) on a single chip to improve performance over single-core processors. As clock speeds became limited, chip designers added multiple cores to allow simultaneous execution of instructions. This achieves performance gains without increasing heat and power consumption. However, multi-core processors introduce new challenges around cache coherence and ensuring software is optimized for parallel execution across multiple cores. Future multi-core designs may include heterogeneous cores specialized for different tasks to further improve efficiency.

1. Multi-core Processors
A COMPARATIVE ANALYSIS BETWEEN SINGLE CORE AND MULTI-CORE
PROCESSORS

2. Outline
1. Introduction
2. Single Core Performance
3. Problems with Single Core
4. Multi-core Solutions
5. Multi-core Advantages
6. Other Incentives
7. Cache Memory in Multi-core Architecture
8. Problems
9. Future of Multi-core

3. What is a Core ?
◦ A Basic Computational Unit of a CPU.
◦ A Core receives instructions, work on it and give results.
◦ A Core is a collection of components such as ALU ( Arithmetic and Logic
Unit ), Registers and Cache memory.
◦ It can run a single thread at a single time. ( Unless it is a Multithreaded Core,
which we'll see in a bit ).
◦ A thread is a small group of instructions with its own PC ( Program Counter ).

4. Single Core Processors
◦ Before the multi-core era, all the processors used to consist of a single core.
◦ A single Core processor is a microprocessor with a single core on the CPU chip.
◦ It can run a single thread at any one time. ( unless Multithreaded ).
◦ With the passage of time the processors became smaller in size, faster and more
efficient.

6. Single Core Performance
◦ Back in that time performance comparisons were based on the clock speeds
of the processors.
◦ Performance gains were achieved by increasing the clock rate of the
processor.
◦ Higher the clock speed faster the execution of instructions.
◦ Apart from clock speed execution optimization and cache were also major
areas of performance gains in single core processors.
◦ Several execution optimization techniques were introduced such as pipelining
and multithreading.
◦ This trend continued for many years.

7. Single Core Performance contd.
◦ Pipelining was introduced for execution optimization.

8. Single Core Performance Contd.
◦ Another technique that was introduced was Multithreading.
◦ Multithreading involves execution of two separate threads.
◦ Time is divided and interlaced between the two threads in order to simulate
simultaneous execution.

9. Single Core Problems
◦ In order to execute tasks even faster you must increase the clock speed but
there is a problem.
◦ The clock speed has reached its limit.
◦ Increasing clock speeds too high increases power consumption and heat
dissipation to extremely high levels.
◦ Different designs are needed which is risky and time consuming.
◦ Cost is also a major factor.

10. Multi-core Architecture

11. Multi-core Processors
◦ The solution came with the introduction of multicore processors.
◦ When increasing the clock speed was no longer an option the chip designers came up with
the idea of incorporating more than one core on a CPU chip to improve performance.
◦ Creating two cores on a single chip increases performance by keeping clock rates at an
efficient level.
◦ A processor with 2 cores and an efficient clock rate can execute instruction with similar
speed to a single core processor running at twice the clock rate.
◦ The processor with two cores will consume less energy.

14. Advantages of Multi-core
◦ Simultaneous Execution
◦ Higher Performance
◦ Instruction Level Parallelism
◦ Lesser Heat Generation
◦ Multithreaded Applications
◦ Thread Level Parallelism

15. Cache memory in Multi-core
Architecture
◦ The first Level ( L1 ) cache is always dedicated to all cores, because it
needs to be accessed quickly.
◦ The Last Level of cache is shared between all the cores. ( Usually they
are L2 or L3 ).
◦ Middle Level Caches can either be shared or merged.

17. Problems and Challenges
◦ Memory / Cache coherence problem. Because we have separate
caches for separate core, how to keep data consistent across caches ?
◦ Multithreading is also a problem, because the software running may
not be designed to take advantage of multicore processor.
◦ This means that a single core does most of the work and the processor
is running no more efficient than a single core processor.

18. The Cache Coherence Problem

24. Future of Multi-core Processors
◦ The Future Multi-core Processors may be Heterogeneous.
◦ Which means all the cores on the chip could be of different types.
◦ Having different cores that specialized in different tasks increases complexity but
has the potential of being much more efficient in speed and power consumption.
◦ If an application only needs to run on a specific kind of a core, performance will be
better.

25. Thank You.