1.1.2 Types of CPU

Question 1

CISC features (6)

Answer 1

Complex instruction set computer

• Larger instruction set
• Each instruction can take multiple FDE cycles to execute
• CISC difficult to pipeline
• More complex circuitry / more transistors (Expensive + more power consumption)
• Many addressing modes available
• Compilers do less work
• Instructions take up less space in memory

Question 2

RISC features (6)

Answer 2

Reduced instruction set computers

• Smaller instruction set
• Each instruction takes one clock FDE cycle to execute
• RISC easier to pipeline
• Fewer addressing modes
• Less complex circuitry / more transistors (Cheaper + less power consumption)
• Compilers do more work
• Instructions take up more space in memory

Question 3

Instruction set architecture

Answer 3

• Includes specification of the set of opcodes implemented by a particular processor - diff processors have different instruction sets so means code is specific.
• Composed by all the instructions a processor can execute
• Group of bytes the CPU can understand

Question 4

GPU’s

Answer 4

CPU - general purpose, GPU - designed for specific task e.g. Graphics

• Thousands of cores to perform single instruction on multiple pieces of data at a time in parallel
• Built in circuitry / instructions for common graphics operations
• Great for graphics and other highly parallelisable problems where large quantities of data need to be processed and task can be broken down
• Great at processing a Single instruction on multiple data items at the same time (SIMD)

Examples :
- Physical Modelling
- 3D Rendering / Modelling
- Data Mining
- Machine Learning

Advantages
- Speed : Through Parallel processing as multi-core processors can handle many tasks simultaneously which speeds up completion
- Efficiency : GPU’s can perform more calculations per unit of power consumed compared to CPU’s when it comes to parallel tasks.

Question 5

Co - processor

Answer 5

Extra processor to supplement functions of primary processor

E.g. Math’s co-processor has large registers so good for FP arithmetic but has otherwise limited functions.

Question 6

Parallel processing

Answer 6

Execute multiple different instructions at the same time across the multiple different independent processing units (cores for multi core or cpus for distributed).

Question 7

Parallel and Multi core architectures Advantages and Disadvantages

Answer 7

Advantages:
- Program split - different parts of the program executed at the same time by different independent cores - shortens time to complete
- Large complex problems can be solved more easily.
- Allows for multitasking on different tasks where multiple applications open and processing of background instructions (Multicore)

Disadvantages:
- Some instructions cannot be run in parallel - dependent on other instructions to complete.
- Program must be designed to have parts executed at same time and to make use of multiple cores- increased complexity
- Overheads in communication between cores