CPU Architecture, Performance & Embedded Systems Flashcards
All 28 cards in this deck
What is the purpose of the CPU?
To fetch, decode and execute program instructions.
True or false? The fetch-decode-execute cycle repeats until there are no more instructions to process.
True. The cycle runs continuously while instructions are available.
What is the function of the Arithmetic Logic Unit (ALU)?
It performs all arithmetic and logical operations on data, e.g. addition, subtraction and comparisons.
What is the function of the Control Unit (CU)?
It controls the fetching, decoding and executing of instructions, and sends control signals to manage hardware and move data around the system.
What is cache in the CPU, and what is it used for?
High-speed memory built into the processor that temporarily holds data and instructions the processor is likely to reuse, so they can be fetched quickly.
What are registers?
Small amounts of extremely fast temporary memory inside the CPU that hold the data and addresses needed during processing.
Which CPU register holds the instruction that is currently being decoded and executed?
The Current Instruction Register (CIR).
What is a bus in a computer system?
A channel of communication that transports data, addresses and instructions between components. e.g. the address bus carries the address from the MAR to memory.
What is Von Neumann architecture?
A design where data and instructions are both stored as binary in the same primary memory, and are fetched and executed sequentially by the CPU using the ALU, control unit and registers.
What does the Memory Address Register (MAR) hold?
The address of the memory location currently being accessed (read from or written to).
What does the Memory Data Register (MDR) hold?
The actual data or instruction fetched from memory, or data that is about to be written to memory.
What does the Program Counter (PC) hold?
The memory address of the next instruction to be fetched. It is incremented by one after its address is copied to the MAR.
What does the Accumulator (ACC) hold?
The data currently being processed and the results of calculations carried out by the ALU.
True or false? The Program Counter stores the next instruction to be executed.
False. It stores the address of the next instruction; the PC and MAR store addresses, while the MDR, CIR and ACC store data or instructions.
What effect does increasing the clock speed have on CPU performance?
More fetch-decode-execute cycles are carried out per second, so more instructions are processed in a given time.
What effect does a larger cache have on CPU performance?
More frequently used data and instructions are held close to the processor, so it spends less time waiting for them to be fetched, improving speed.
What is a CPU core, and what effect does having more cores have on performance?
A core is a processing unit that can fetch, decode and execute its own instructions; more cores allow more instructions to be processed simultaneously.
True or false? Overclocking a CPU raises its clock speed with no drawbacks.
False. It increases performance but can overheat the CPU and cause long-term damage.
What is an embedded system?
A small computer built into a larger device, which controls that device and usually performs only one or a limited number of tasks.
Give three typical characteristics of an embedded system.
It has a specific purpose (one or a limited number of tasks); it is built within a larger device; its software is in firmware/ROM and is hard to change.
Give three examples of embedded systems.
e.g. a dishwasher, a digital watch and a car engine management system. (Also central heating, GPS, fitness trackers, calculators.)
True or false? A laptop is an embedded system.
False. A laptop is a general purpose computer that can run many different programs chosen by the user.
Give two differences between an embedded system and a general purpose computer.
An embedded system performs only one or a limited number of tasks and is not usually programmable by the user; it uses a cheaper, less powerful processor and needs less power.
What are the steps to decide which of two CPU specifications will perform better for a stated purpose?
e.g. CPU A: 4 cores, 2.0 GHz; CPU B: 2 cores, 3.2 GHz — for video editing software that uses all cores- Compare each characteristic: A has more cores, B has the higher clock speed.
- Match them to the task: video editing splits work across cores.
- Choose and justify: CPU A, as more instructions are processed simultaneously.
True or false? The CPU with the higher clock speed will always be the better performer.
False. Cache size and number of cores also affect performance, so a slower CPU with more cores or a larger cache may perform better.
What is the effect on performance of increasing clock speed, cache size and number of cores together?
The greatest performance improvement: more cycles per second, less waiting for data to be fetched, and more instructions processed simultaneously.
What are the steps to explain why a device in a given scenario is an embedded system?
e.g. the control system inside a washing machine- Say it is built within a larger device: built into the washing machine.
- Give its purpose: dedicated to one/limited task, controlling the wash cycles.
- Add one more characteristic: its software is in ROM/firmware, so it is hard to change.
True or false? A television is not an embedded system because it can do more than one thing.
False. A TV is an embedded system — a microprocessor and built-in software are built into the device to control it and perform a limited set of tasks.