1.1 Systems architecture

What is the purpose of the CPU?

• To process data and instructions by constantly repeating the fetch decode execute cycle

Describe the fetch-decode-execute cycle

• Fetch

  • The program counter stores the memory address of the next instruction to be processed

  • This memory address is copied into the MAR

  • The program counter is incremented by 1

  • The CPU checks the memory address in RAM which matches the address held in the MAR

  • The instruction/ data is transferred to the MDR

• Decoded

  • The instruction is decoded by the control unit

• Execute

  • The instruction is executed

  • Any result of an execution is stored in the accumulator

  • The cycle repeats

What is the function of the ALU?

Arithmetic logic unit

• Performs mathematical calculations and logical operations

What is the function of the CU?

Control unit

• Sends control signals to control the flow of data around the CPU

• Decodes instructions

What is the function of cache?

Cache is very small very fast main memory located on or nearby the CPU; it stores frequently accessed data and instructions

• It is slower to access than registers, but faster than RAM

Describe the function/s of the registers

Registers are small amounts of high speed memory used to temporarily store small amounts of data needed during processing

• Program counter

  • Stores the memory address of the next instruction to be fetched from memory

• Memory address register

  • Stores the memory address of the current instruction that is to be fetched from memory, or the address in memory in which data is to be stored

• Memory data register

  • Stores the data/ instruction that has been fetched from memory or is to be written to memory

• Accumulator

  • Stores the result of mathematical calculations or logical operations

Define Vonn Neumann architecture

A computer with Vonn Neumann architecture stores both program instructions and data in the same memory and format (in binary)

Explain the characteristics of CPUs that affect their performance

• Clock speed

  • Clock speed is the number of FDE cycles a CPU can perform per second; the faster the clock speed, the faster the computer can perform the FDE cycle, resulting in better performance because more instructions can be processed per second

• Cache size

  • Increasing cache size allows more frequently used data and instructions to be stored in the cache. This reduces the number of times the CPU has to access slower main memory (fewer cache misses). As a result, the CPU can fetch and execute instructions more quickly, so overall CPU performance increases

• Number of cores

  • Instructions can be executed simultaneously, increasing performance. However, not all programs make use of multiple cores

Give the unconventional factors that affect CPU performance

• Increasing size of RAM

• Graphics card

• SSD

• HDD

What is an embedded system?

A smaller computer system built into a large machine with a defined/ limited function

Give the characteristics of embedded systems

• Low processing power

• Small amount of storage

• Program is stored in ROM

• Limited user interface

Give examples of embedded systems

• Traffic lights

• Dish washers

• Washing machines

• Central heating systems