CPU
Central Processing Unit
- function is to process data and execute instructions
- measured in hertz
- 1 Hertz= 1 FDE cycle per second
FDE cycle-fetch
- PC passes an address to MAR
- PC is incremented (goes up by one )
- Address in MAR is passed to memory
- Instruction is fetched from memory
- Fetched instruction is placed in MDR
FDE cycle-decode
-Instruction is passed to CIR and decoded
FDE cycle-execute
- The decoded instruction is then executed
- The process is repeated
What is Von Neuman Architecture?
FDE cycle
factors that affect CPU performance-Cores
- Cores are where FDE cycles take place
- Single core can only execute one FDE at once
- Multiple cores can execute multiple FDEs at the same time
factors that affect CPU performance-Clock Speed
- Measure in Hertz (normally measured in gigahertz-1 billion)
- A measurement of the number of FDE cycles that can be completed in one second
factors that affect CPU performance-Cache
- Stores frequently used data and instructions
- It’s faster to transfer to and from cache than it is from RAM
- This makes the CPU more efficient
what else can affect performance of CPU?
RAM, HDD, SSD
optional-graphics card (GPU)
Embedded System
A computer system built into another device and has a specific purpose e.g.
- Microwave
- Sat-Nav
- Dishwasher
- DVD player
Describe RAM
Random Access Memory
- Volatile- needs power to retain data
- Stores currently used data and instructions and memory
- 1024MB=1GB
Describe ROM
Read Only Memory
- Non-volatile-doesn’t need power to retain data
- Stores the boot up instructions
Secondary Storage
To store data and progress e.g. operating system
-Secondary storage is persistent (Data is saved even when the power is turned off)
-Magnetic
Cheap per MB/GB (cheapest)
Large Capacity
Sensitive to movement (fragile) due to moving parts
Relatively slow to access
-Solid State
No moving parts, therefore not sensitive to
movement
Portable ,lightweight and requires less power
Relatively expensive per MB/GB
Smaller capacities than magnetic
Faster access due to no moving part
Virtual Memory
- Use of secondary storage as RAM
- Stores contents of RAM
- When there isn’t enough physical space in RAM
Developments in memory
- Memory clips have become physically smaller
- Whilst increasing their capacity
- Memory has become faster to access
- Memory has become cheaper per byte/kB/MB
