1.1 Characteristics of Contemporary Processors

What is the function of the arithmetic logic unit (ALU)?

Performs arithmetic calculations such as addition and subtraction on floating point numbers and boolean logic

What is the function of the Control Unit (CU)?

Controls and coordinates the activities in the CPU

Decoding instructions

Uses control signals to enable data to be read and written to and from main memory

Name the CPU's registers and their function

Program counter (PC) - holds the address of the next instruction to be executed

Accumulator (ACC) - stores the results of the ALU

Memory address register (MAR) - temporarily holds the address of the instruction being read or written

Memory data register (MDR) - temporarily holds the data being read or written

Current instruction register (CIR) - holds the current instruction being executed

What are the 3 buses in the CPU?

Address bus - transmits the memory address of an instruction

Data bus - transports data to and from components

Control bus - transmits control signals to internal and external components

Describe the fetch stage of the FDE cycle

PC copies address of next instruction to MAR

Instruction held at the address is copied to the MDR by the data bus

PC is incremented by 1

The contents of the MDR is copied to the CIR

Describe the decode stage of the FDE cycle

The contents of the CIR and split into operand and opcode

How does clock speed affect CPU performance?

The higher the clock speed, the greater the number of instructions that can be carried out per second

What are the factors affecting CPU performance

Clock speed

Number of cores

Cache size

How does the number of cores affect CPU performance?

The more cores, the more FDE cycles can occur per second

What is cache memory?

Stores the most frequently used instructions and data

What is pipelining?

The process of completing the fetch, decode and execute of three separate files simultaneously.

Describe the Von Neumann architecture

Processor containing registers in which a shared data bus is used for both data and instructions

Describe the Harvard architecture

Separate memory locations for data and instructions

No registers

Normally used in embedded systems

Advantages of Von Neumann Architecture

Cheaper to develop as the control unit is easier to design

Programs can be optimised in size

Advantages of Harvard Architecture

Quicker execution as data and instructions can be fetched in parallel

Memories can be different sizes, which can make more efficient use of space

What is contemporary processing?

Combination of VN and Harvard. VN is used when working with data/instructions, Harvard is used to divide cache into instruction cache and data cache

What is a RISC processor?

Small instruction set

Executes in one line of machine code

What is a CISC processor?

Large instruction set

Try to execute instructions in as few lines of code as possible

Replaced by RISC

What is a GPU?

Processing unit containing multiple processors which work in parallel

Good at performing repetitive tasks such as image processing or machine learning

Optical storage

Optical devices are read using lasers, binary information is either in pits or lands. The laser light scatters when there is a pit, pits represent a 0 and lands represent a 1.

Examples of optical storage

• CD (compact discs) - easily damaged, low capacity, portable

• DVDs - higher capacity than CDs

• Blu ray - 5x more capacity than CDs

Magnetic storage

Devices that use magnets to reprent binary information - if a portion of the magnetic material is polarised, the data can be read as a 1 by the head. If it is unpolarised it cant be read = 0.

Hard disk drive

• High capacities (500GB - 5TB)

• Slow transfer speeds

• Fragile due to moving parts

Solid state / flash storage

• Uses electrical charges to represent either binary 1s or 0s.

• Large capacity

• Portable

• Robust

• Expensive

• Non-volatile

Example of flash storage

Solid state drives (SSD) - very large capacity, portable, no moving parts, expensive

Read only memory (ROM)

• Non volatile

• Contents cannot be changed

• Contains the bootstrap instructions for the computer

Random access memory (RAM)

• Main memory that temporarily stores the programs the computer is using

• Volatile

• Faster than secondary storage

Virtual storage

Storing data over the internet on a cloud server rather than on a physical storage device

• Convenient

• “limitless” amount of storage

• Data can be shared

• Requires internet access

• Expensive