1. 1.1 The Characteristics of Contemporary Processors, Input, Output and Storage Devices
1.1.2 Types of Processors

2. Types of Processors
There are different types of CPUs in existence. For example, there are the Intel 80x86 processors upon which today’s home computers are based (also known as IBM compatibles and variations thereof). With these types of processors, you can load up operating systems such as Windows and Linux.
Then there are the 680x0 processors upon which Apple Macintosh’s are based. Each type of CPU has its own set of machine code instructions that it can work with. All of the instructions together for any particular CPU are known as the CPU’s 'instruction set'.
One type of CPU will not be able to use the same instruction set as a completely different CPU.
This is one reason why software created for Microsoft Windows does not work on Apple’s Macintosh.

3. CISC
The types of processors on the previous slide are sometimes referred to as CISC, or Complex Instruction Set Computers. These processors can do complex operations, which can be carried out in just one instruction. They have a wide range of instructions that can be used.
For example, a CISC processor might have a 'complicated' instruction designed into the hardware called 'POWER'. This can take one number from a register, find the power of that number, held in a different register, and then store the result in yet a third register. So, 2 to the power 4 would be calculated as 16 and this would be stored in a third register. This would all be done using one complex instruction, which might take about 3 or 4 CPU clock cycles to complete.

4. RISC
There are also CPUs that are known as RISC, or Reduced Instruction Set Computers. RISC processors use a much smaller, simpler set of instructions than CISC processors and so to carry out any particular programming task may take many ‘fetch decode execute’ cycles. RISC processors, however, are much more efficient at processing huge blocks of data than CISC.
In the previous example of calculating 2 to the power 4, a RISC processor would:
first load 2 from memory into a register using a simple instruction
then load 4 into another register using another simple instruction
then the calculation would then be done using another instruction
and finally, an instruction would store the result.

5. CISC Vs. RISC
The RISC processor in the previous example would take 4 instructions compared to the CISC processor, which might take just 1.
This might seem less efficient at first, because you have more instructions and you need more RAM to do the calculation. Each of the instructions in a RISC processor would take just 1 clock cycle by design so overall, the speed of executing the instruction should be about the same as the CISC approach.
However, because RISC processors hardware is far simpler, they can make use of far more general registers for computations, which can speed up processing considerably for blocks of similar data.

6. CISC Vs. RISC
CISC processors use instructions that are designed for the hardware, so relatively little compilation (compiling code) is required. The instructions themselves can include multi-clock cycle instructions and require very little RAM compared to RISC instructions. This means smaller programs.
Writing programs for CISC computers may be easier as the instructions are similar to those found in high level languages. You don't have to include instructions that manipulate registers, for example, as you would need to do in a RISC program.

7. Activity 1 - Video
Watch this video on CISC Vs. RISC processors.

8. Activity 2
Spend 10 minutes carrying out some Internet research to find out the benefits and drawbacks of CISC and RISC processors.
Note down each benefit and drawback down that you find on paper.
You will then be paired up to discuss and share the information you have found out about both types of processors.
On A4 Paper

9. Activity 3 - Exam Question Practice
Q State three features of Complex Instruction Set Computer (CISC) architecture. (3) 1 2 3

10. Activity 3 - Exam Question Practice
Q Explain one disadvantage, other than cost, of a CISC architecture compared with a Reduced Instruction Set Computer (RISC) architecture. (2)
A Type your answer here..

11. Graphical Processing Unit (GPUs)
The CPU is often introduced as the brain of the computer. A lot of the processing that is done by modern computers, mobile phones, tablets and so on, however, is now done by a GPU, or Graphical Processing Unit.

12. Graphical Processing Unit (GPUs)
GPUs were originally designed to process the huge amounts of similar data needed to display images, especially 3D images and moving graphics.
These kinds of tasks are very intensive and if a computer's CPU had to carry them out, the whole system might slow down to unacceptable levels. A GPU can take over this role and ensure that the overall computer system isn't compromised in any way.
These kinds of tasks are very intensive and if a computer's CPU had to carry them out, the whole system might slow down to unacceptable levels. A GPU can take over this role and ensure that the overall computer system isn't compromised in any way.
GPUs cannot do all the things that a CPU can, however. A CPU working together with a GPU often creates the best combination of price, power, efficiency and performance in a computer system.

13. Graphical Processing Unit (GPUs)
CPUs were not designed to process huge blocks of similar data in the way the GPUs were designed. CPUs were designed to carry out a whole range of more general purpose tasks. CPUs have a limited number of individual processors within them, called cores. Each core in a quad core processor, for example, can work on part of a program and speed things up compared to a single core CPU.
GPUs by contrast typically have hundreds of cores and work far faster than any CPU can. In addition, GPUs typically use less power than CPUs and cost less to produce.

14. Activity 4 - Video
Watch this video on GPUs and their uses.

15. Activity 5 - Exam Question Practice
Q State two advantages a GPU has over a traditional CPU when processing large amounts of similar data. (2)
A Type your answer here..
Q State one disadvantage of a GPU over a traditional CPU. (1)
A Type your answer here..

16. Parallel & Multicore Architectures
Parallel Processors
Rather than have one processor executing programs, you could have more than one. This is sometimes referred to as a Supercomputer. This would greatly increase the speed that programs could be executed – a major advantage of this kind of processing.
Different parts of the same program could be executed simultaneously, each processor dealing with a particular task. Of course, this assumes that the original program was designed to have parts of it executed at the same time. Most programs are not designed in this way and this adds an extra degree of complexity to writing software – a disadvantage of parallel processing.

17. Parallel & Multicore Architectures
Parallel Processors
When programs are written to use parallel processing, however, great improvements in the speed of processing are seen, for example, in weather forecasting because this requires a lot of mathematical processing. One possible layout for a parallel processing system is shown in the diagram.

18. Parallel & Multicore Architectures
Parallel Processors
In this system, there are a number of CPUs working together, sharing the same memory. The processing that all these CPUs do will greatly increase the demands on the data bus - each CPU needs to get data to and from memory and only one CPU can use the data bus at any one time.
To help reduce the time one processor waits for access to the data bus, each CPU has its own cache. Data and instructions can then be transferred to it in one go and the CPU can get on with processing it without constantly requiring memory access.
Now a CPU will be waiting much less than before. The provision of a data bus for each CPU will further improve performance because the CPUs will not have to wait for access to the only available bus.

19. Parallel & Multicore Architectures
Pipeline Processors
In the conventional Von Neumann architecture, an instruction is fetched, then decoded and finally executed. This happens in sequence. It would be nice if an instruction could be fetched and then, while it is being decoded, another instruction is fetched, and while the decoded instruction is being executed, other instructions are being fetched and others still decoded - all at the same time.
A processor that is designed to do just this is known as a pipeline processor. As with parallel processing, programs need to be written to take full account of this capability.

20. Parallel & Multicore Architectures
Array Processors
An array processor is designed to allow a single machine instruction to operate on lots of different data sets at the same time. If you have lots of data that all have to be processed in the same way, than this can be a very fast way of carrying out processing.
An array processor is known as a Single Instruction Multiple Data computer (SIMD). Weather forecasting and airflow simulations around planes, for example, are very good examples where array processors might be useful.

21. Parallel & Multicore Architectures
Maths Co-Processors
Another kind of processor is a Maths co-processor. This is a specialised processor that works in addition to the main processor. It has large registers and specialist functions that can manipulate big floating-point numbers easily. Whilst it is doing this, the main CPU is free to work on other things.
Maths co-processors reduce the time that CPUs have to spend working on floating-point numbers, a task which they can do but not in one go – they are not specifically designed for that.

22. Parallel & Multicore Architectures
Multicore Processors
A CPU traditionally had one core but processors these days might be dual-core or quad-core, for example. A core is actually a processor with its own cache. So a dual-core CPU has not one but two processors. A quad core CPU has four processors. Two brains (or four brains) are better than one.
Each processor can be working on different parts of a program at the same time and so this speeds up the overall CPU's performance.

23. Activity 6 - Video
Watch this video on multicore and parallel processor architectures.

24. Activity 7
Use this website to create a crossword. It should feature the five types of processors you have learnt about on the previous slides.
You need to come up with a clue for each processor type.
Once completed, paste your crossword into the box on the next slide below along with the clues.
You can then swap crosswords with someone else in the class and complete each others.

25. My Crossword
Paste your crossword and clues in the box below.

26. Activity 8 - Exam Question Practice
Q State two advantages of each processor in a parallel processor each having their own cache and buses. (2)
1 Type your answer here..
2 Type your answer here..
Q Describe what is meant by and give an advantage of a multicore processor. (2)
A Type your answer here..