1.1.2 Types of Processors

CISC

Complex Instruction Set Computer

Tries to reduce the number of instructions that a program has by combining many simple instructions into a single complex one.

Attributes of CISC

- Large instruction set
- Complex instructions
- Clock ticks slightly slower
- Each instruction make take many cycles and so program runs slower
- Less use of RAM
- Variable number of bytes and so instructions are larger than size of word
- Hardware is more complex and bigger
- More transistors so consumes more power and requires heat sink/fan
- More transistors = more cost
- Used in desktops, PCs and Laptops

RISC

Reduced Instruction Set Computer

They have more instuctions, but they reduce the number of cycles that an instruction takes to perform

- Programs run faster due to smaller instructions
- Small instruction set

Attributes of RISC

- Limited number of instructions
- Simple processor design
- Each instruction takes one cycle so program runs quicker
- Heavy use of RAM
- Fixed number of bytes
- Hardware is simpler and smaller in design
- Used fewer transistors, so doesn't get as hot
- less transistors = less cost
- Used in smartphones and tablets

Concurrent

At the same time

Pipeline

SISD
Inside CPU
Overlaps the Fetch-Decode-Execute cycle
Can't be done with branching statements and things that require human input

SISD

Single Instruction Single Data
1 instruction on one piece of data

Array processor

SIMD
Graphics cards, games consoles
A single instruction is issued by the control unit and is applied to a number of data sets at the same time

SIMD

Single Instruction Multiple Data
Same instruction to lots of pieces of data

Multi-core

MIMD
Super computers, modern multi-core chips

MIMD

Multiple Instruction Multiple Data
Lots of different instructions to lots of different pieces of data

Advantages of parallel processing

-Faster when handling large amounts of data, with each data set requiring the same processing (array and multicore methods)
-Not limited by the bus transfer rate (no von-Neumann bottleneck)
-Can make maximum use of CPU (pipeline method) in spite of the bottleneck

The GPU does not speed up the CPU, but it takes some of the calculations away from the CPU so that it can do other calculations, speeding up the system

Disadvantages of Parallel Processing

-Only certain types of data are suitable for parallel processing. Data that relies on the result of a previous operation cannot be made parallel, for parallel processing, each data set must be independent of each other.
•More costly in terms of hardware - multiple processing blocks needed, this applies to all three methods

Co-Processor

Especially designed to carry out floating point calculations extremely quickly and works with the CPU on the motherboard.
Advantage:
Calculation (and hence performance) is much faster.
Disadvantages:
- more expensive,
- requires more motherboard space
- takes more power.
- only has a limited range of functionS

GPU

Graphics Processing Unit which is designed to handle graphics and video much faster than the CPU itself
They have instruction sets which relate specifically to graphics processing
Has 1000s of cores designed for handling multiple tasks at the same time
Used as a co-processor

Co-Processing VS Parallel Processing

• Both involve more than one processor working together to perform a single job with each job being split into smaller tasks.

• Parallel processors can use any processor for a task -whereas co-processors only perform specific types of task e.g. floating point calculations. The task is only completed more quickly in a co-processor if it is a suitable task.

• Parallel processors need a more complex OS than co-processors as it needs to control how tasks are broken down and spread across all available cores

GPU disadvantages

• expensive.
•do not improve CPU performance on all tasks, only ones related to graphics and video.
•use a lot of power needs a more powerful power supply.
• need a cooling fan = noisy .

Three types of parallel processing

Pipelining, array processor, multicore