Topic 3 - Computers Flashcards
What is a CPU for?
A processing unit to decode and execute program instructions fetched from memory one at a time.
What is the input and output for?
Input and output mechanisms to input programs and data and output the results of processing.
What is the main memory for?
A memory unit into which program instructions and data are loaded prior to being processed.
Describe the features of a main memory unit.
- It is short-term, working memory.
- It only holds the program instructions and data that the CPU is currently using.
- The contents of the main memory are continually changing.
- It consists of a collection of storage locations, each with its own unique address.
- A storage location can hold a program instruction or item of data.
- It is often referred to as RAM
Is the main memory short-term or long-term?
Short-term working memory. It only holds the program instructions and data that the CPU is currently using. The contents of the main memory are continually changing.
What does the main memory consist of?
It consists of a collection of storage locations, each with its own unique address. A storage location can hold a program instruction or item of data.
What is the main memory often referred to as?
RAM (random access memory). Because storage locations can be read from and written to in any order.
Why is the main memory classed as primary storage?
Because the CPU has fast, direct access to it.
Why is it described as volatile?
It needs power to retain its contents. When the computer is switched off, its main memory is completely wiped.
What is the CPU?
The hardware component that decodes and executes program instructions.
What are the names of the three busses in the CPU components?
- Address bus
- Data bus
- Control bus
What do the three buses do?
They work together to transfer data between the CPU, main memory and input/output devices such as the keyboard and screen.
What does the control unit do (in the CPU)?
Fetches program instructions from main memory one at a time, decodes them and directs the operations of the other parts of the system to execute them.
What are the seven components of the CPU?
- Address bus
- Data bus
- Control bus
- Clock
- Control unit
- Arithmetic logic unit
- Registers
What does the clock do (in the CPU)?
Synchronises the actions of the CPU.
What does the ALU do (in the CPU)?
Performs arithmetic and logic operations on data.
What does the register do (in the CPU)?
Direct-access storage for instructions, intermediate results and data within the CPU. Some are general purpose. Others, such as the Program counter and the Instruction register, have specific functions.
What is the clock?
A tiny quartz crystal that vibrates at a constant rate. Each tick of the clock triggers the CPU to carry out one action.
What is the clocks speed measured in?
Cycles per second: 1 hertz = 1 cycle per second.
What is a bus?
A collection of wires that is used to transfer data between components of a computer system.
What does the control bus do?
Carries signals between the CPU and other parts of the computer system.
What does the address bus do?
Holds the address of the memory location that the CPU will read from or write to. The number of wires in the address bus (its bandwidth) determines how much addressable memory there is.
What does the data bus do?
Transfers program instructions and data between memory and the CPU.
What is the fetch-decode-execute cycle?
It is the sequence of steps carries out repeatedly by the CPU when a program is being executed. Instructions are fetched one at a time from memory into the CPU, where they are decoded and executed.
What are the three stages of the fetch stage?
- The CPU places the memory address of the next instructions on the address bus
- The CU within the CPU sends a read signal along the control bus to memory
- The content of the specified memory location is transferred along the data bus to the CPU. On arrival, it is stored in one of the CPU’s registers
Explain the decode stage.
The CU looks up the instruction in the CPU’s instruction set.
Each CPU has its own unique instruction set - a list of all the operations that it can carry out.