Registers
This register holds the instruction that is currently being executed by the CPU.
CIR (Current Instruction Register)
What's the purpose of the CPU?
The purpose of the CPU is to process data and instructions by constantly repeating the fetch - decode - execute cycle.
What is an F-D-E cycle?
The essential idea of the F-D-E cycle is that instructions are fetched from RAM, to be decoded (understood) and executed (processed) by the CPU.
What 3 main factors affect the performance of the CPU?
Cache Memory, Clock Speed, Number of Cores
Say two things about primary storage
Very quick because it is directly accessed by the CPU. Typically smaller in storage size.
Sometimes called ‘main memory’.
Includes RAM and ROM.
This register holds the address of the location in memory where data or instruction can be retrieved or stored.
MAR (Memory Address Register)
What are the 4 main components of the CPU?
ALU, CU, Cache, Registers
Where is the instruction in the MDR copied into?
The instruction in the MDR is copied into the Current Instruction Register (CIR).
How does cache memory improve performance?
Cache memory is closer to the CPU than RAM, meaning that it can provide data and instructions to the CPU at a faster rate.
A computer with more cache memory (e.g. 8GB instead of 4GB) should have a higher performance because repeatedly used instructions can be stored and accessed faster.
Say two things about secondary storage
Slower because it is not directly accessed by the CPU.
Typically larger in storage size.
Used for the long-term storage of data and files because it is non-volatile.
Includes magnetic, optical and solid state storage.
This register stores information that is being sent to or received from the memory along the bidirectional data bus.
MDR (Memory Address Register)
What's the purpose of the Cache?
Cache memory is used to temporarily store data that is frequently accessed.
Where is any result of an execution stored in the CPU?
Any result of an execution is stored in the Accumulator (ACC) register.
What is clock speed?
Clock speed is the measure of how quickly a CPU can process instructions. A typical desktop computer might have a clock speed of 3.5 GHz. This means it can perform 3.5 billion FDE cycles a second.
Explain what volatile storage is and give an example
Volatile storage is temporary - data is lost whenever the power is turned off.
Example: RAM
This register is connected to the internal address and is used to store the address to access memory.
PC (Program Counter)
What changed with the Von Neumann architecture?
This architecture is named after John von Neumann who developed the concept of a stored program computer. Before being able to store programs in memory, instructions had to be manually input by a human.
A computer with Von Neumann architecture stores both program instructions and data in the same memory (RAM).
Say one thing that happens before the CPU checks the address in RAM which matches the address held in the MAR
The Program Counter (PC) register displays the address in RAM of the next instruction to be processed.
This value is copied into the Memory Address Register (MAR).
The PC register is increased by 1.
This prepares the CPU for the next instruction to be fetched.
Why might having more cores not always result in better performance?
If one core is waiting for another core to finish processing, performance may not increase at all.
Some software is not written to make use of multiple cores, so it will not run any quicker on a multi-core computer.
Explain what non-volatile storage is and give an example
Non-volatile storage saves the data even when not being powered. Data can be stored long-term and accessed when the computer is switched on.
Example: ROM
This register is used to store data that is being worked on by the ALU and is the key register in the data section of the CPU.
Accumulator
When was the Von Neumann architecture invented?
In the 1940s
What happens after the PC register displays the address in RAM of the next instruction to be processed and that is copied into the Memory Address Register (MAR).
The PC register is increased by 1.
Why don't all computers have much more cache since it's so fast and efficient?
Cache memory is costly, so most computers only have a small amount.
What is ROM and what is stored in it?
ROM is non-volatile storage that cannot be changed.
ROM stores the boot program / BIOS for when the computer is switched on. The BIOS then loads up the operating system to take over managing the computer.