1.1
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Explain what happens in the ‘fetch’ stage of the FDE cycle?
• CU signals for address of an instruction in the PC is loaded into the MAR • The data in that memory address is fetched from memory and stored in the MDR • PC is incremented to point to the address of the next instruction
Explain what happens in the ‘decode’ stage of the FDE cycle?
• Instruction is decoded by the control unit
Explain what happens in the ‘execute’ stage of the FDE cycle?
• Fetching data from memory • Jumping to another instruction • Writing data back to RAM • Calculation is performed • Whole FDE process is repeated
What is clock speed?
• The number of FDE cycles executed per second • Measured in GHz • Faster = more instructions can be executed
What is cache?
• Small amount of very fast memory that temporarily stores recently used instructions • Level 1 is the fastest but it has the smallest capacity
What are cores?
• A complete copy of CPU (processing unit) • More cores = more tasks can be executed at once (but requires communications and some softwares are not designed to make use of multicores therefore does not equal to double speed)
What are the factors affecting the speed of the CPU?
• Clock speed • Number of cores • Cache size • RAM size
What is the control unit?
• Decodes and executes instructions • Sends signals to control how data moves around the CPU
What is the arithmetic logic unit?
• Performs mathematical calculations • Makes logical comparisons
What are registers?
• Tiny and super fast memory holding a single instruction/address
What are the four registers?
• Accumulator • Memory Address Register • Memory Data Register • Program Counter
What is the accumulator?
• Holds results of calculations performed by the ALU
What is the memory address register?
• Stores the address of current instruction/data to be fetched from or stored in memory
What is the memory data register?
• Stores the data which has been fetched from or is to be written to memory
What is the program counter?
• Stores address of next instructions to be run • Once instruction is fetched, value is incremented by one
What is an embedded system?
• Has limited functions • Built into a larger machine • Cannot be modified once manufactured (read only) • Program controlling them is stored in ROM
Give some examples of an embedded system
• Washing machine • Smart watch • Air conditioning • Alarm clocks
What are the benefits of embedded systems?
• Highly efficient as firmware has very close control over the hardware • Easy to design because less components are required • Cheap to produce • Low in power consumption due to limited tasks to be executed • Compact in size
State the purpose of the CPU
• To process instructions requested by the user • To fetch, decode and execute them
Explain what is meant by a computer system
• An electronic device that takes input, processes data and delivers output
What is the name of the computer architecture that is the basis of most digital computer systems?
• Von Neumann architecture
What is the FDE cycle?
• Fetch decode execute • Complete process of retrieving an instruction, decoding it and carrying it out