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FlashcardsWhat is a Computer?
A computer is an electronic device which takes input, processes data, and delivers output.
What does CPU stand for?
CPU stands for Central Processing Unit.
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71 Terms
What is a Computer?
A computer is an electronic device which takes input, processes data, and delivers output.
What does CPU stand for?
CPU stands for Central Processing Unit.
How does a computer carry out its functions?
A computer carries out its functions through the Fetch-Decode-Execute Cycle.
What is the Fetch stage of the FDE cycle?
In the Fetch stage of the FDE cycle -
The CPU fetches the next instruction from the main memory.
What is the Decode stage of the FDE cycle?
In the Decode stage of the FDE cycle -
The CPU inspects the instruction and works out what it is that needs doing.
What is the Execute stage of the FDE cycle?
In the Execute stage of the FDE cycle -
The CPU carries out the instruction.
What is Clock Speed? What is it measured in?
Clock Speed is the speed at which the FDE cycle is done. It is measured in hertz.
The CPU is often referred to as the … of the computer system?
The CPU is often referred to as the brain of the computer system.
What does the ALU stand for and what does it do?
The Arithmetic Logic Unit is responsible for carrying out arithmetic calculations and making logical decisions.
What does the CU stand for and what does it do?
The Control Unit sends signals to control how data moves around the CPU.
What does the Cache do?
The cache provides fast access to frequently used instructions and data. It is a small amount of very fast memory.
What are the Registers?
The Registers are tiny, super fast pieces of onboard memory inside the CPU. They each have a very specific purpose -
Accumulator
Program Counter (PC)
Memory Address Register (MAR)
Memory Data Register (MDR)
What is a fixed program computer?
A fixed program computer doesn’t have changeable programs.
Calculators - only for mathematics, can’t do anything else.
What is a stored program computer?
Stored program computers have changeable programs.
Who designed the first stored program computer? What name was given to this way of programming computers?
John Von Neumann designed what became known as the Von Neumann Architecture.
What are the key characteristics of the Von Neumann Architecture?
The VNA:
CPU
CU
ALU
Onboard Cache
Internal Clock - provides a pulse at a constant rate to synchronise components.
What does the Program Counter (PC) do?
The PC holds the address of the next instruction to be executed in memory.
What does the Memory Address Register (MAR) do?
The MAR holds the address of where data is to be fetched from or stored into.
What does the Memory Data Register (MDR) do?
The MDR holds any data which has been fetched from memory or is about to be written to memory.
What does the Accumulator do?
The accumulator holds the results of calculations performed by the ALU.
What is the Fetch stage of the cycle? Use the registers in your answer.
Fetch -
The PC is checked as it holds the address of the next instruction to be executed.
This address is used by the MAR to fetch the instruction needed from the main memory and bring it to the MDR.
The address in the PC is incremented to point at the next instruction.
What is the Decode stage of the cycle? Use the registers in your answer.
Decode -
The CU decodes the instruction to see what has to be done.
What is the Execute stage of the cycle?
Execute -
The instruction has now been executed.
What is done to execute it depends on the instruction itself.
What does the processing power of a CPU depend on?
The processing power of a CPU depends on -
Clock Speed
Number of Cores
Cache Size
What is clock speed measured in?
Clock speed is measured in hertz.
(number of cycles per second)
What clock speed do modern processors operate at?
Modern processors operate at Gigahertz (GHz)
What is the cache?
The cache is a temporary storage of data and instructions being read to and written from the main memory.
Every time this happens, a copy of the data is kept in the cache.
Where is the cache located?
The cache is located on the board or very near to the CPU.
Why is the cache important?
It is much quicker to get items from the cache than from RAM, therefore CPUs try to avoid getting instructions from RAM as much as possible as it costs time.
What is a core in a CPU in simple terms?
A core is a complete copy of the CPU.
How many processing units would a quad core processor have?
A quad core processor would have 4 separate processing units - each with own:
Registers
ALU
CU
Etc.
More cores = …?
More cores = More power
Why do more cores cost time and efficiency?
Because CPU cores must communicate with each other.
Does doubling the number of cores directly double the power of the CPU?
No. Doubling the number of cores doesn’t directly double the power of the CPU.
What effect would increasing:
The number of cores
The cache size
The clock speed
have on a CPU?
The CPU would be faster, more efficient, and more powerful. However, it would likely be more expensive.
What are embedded systems?
Embedded systems are systems which are dedicated to a specific task.
Since embedded systems are dedicated to a specific task, what does that mean the design engineers can do?
Design Engineers can optimise the systems to -
Reduce the size of the product
Reduce the cost of the product
Increase the reliability for the given task.
Embedded systems are usually mass produced, therefore…?
Embedded systems are usually mass produced, therefore we can get further benefits from economics of scale.
What are the properties of embedded systems compared to general purpose systems?
Properties of embedded systems compared to general purpose systems -
Low power consumption
Small size
Rugged Operating System
Low cost per unit
More difficult to program and interact with (limited processing resources)
What are some examples of embedded systems?
Examples of embedded systems -
Apollo Guidance Computer for moon missions (one of the earliest examples)
Hospital instruments
Car engine management systems
Digital clocks
What percentage of all processors are manufactured as components of embedded sytems?
98% of all processors are manufactured as components of embedded systems.
CPU
central processing unit, contains ALU, CU, registers and cache, controls all the processing.
ALU
arithmetic logic unit. completes all calculations and performs logical operations, contains the accumulator.
cache
stores regularly used data so CPU can access it, slower than register faster than RAM, low capacity and expensive.
program counter (PC)
tracks RAM address of next instruction.
memory data register (MDR)
stores the data that is transferred from RAM to the CPU
memory access register (MAR)
tracks RAM address of data that is currently being accessed.
accumulator
stores the result of executions in the FDE cycle
FDE cycle
fetch ——> decode ——> execute
memory address held in the PC is copied into the MAR.
address in PC is then increased by one.
processor sends a signal along the address bus to the memory address held by MAR.
instruction/ data held in that memory address is sent along the data bus to the MDR.
data in MDR copied into CIR.
data in MDR is decoded then executed. results are stored in ACC.
cycle returns to step one.
current instruction register (CIR)
stores instructions that have been fetched from RAM.
embedded system
computers built into other devices that are dedicated to a single task, used as control systems monitoring and controlling machinery to achieve a desired result.
clock speed
measure of how quickly a CPU can process instructions, the faster the clock speed the quicker the instructions are processed.
cores
each processor has a core in which instructions are executed, each core completes instructions independently.
GPU
graphics processing unit, improves quality of graphical content.
virtual memory
computers have a limited amount of RAM , as applications are opened RAM fills up with data, it needs somewhere else to put the data, it will be moved to secondary storage e.g hard drive.
RAM
random access memory, main memory in a computer, volatile (memory wiped when power goes off) when a computer boots up its copied from secondary storage to RAM.
ROM
read only memory, non-volatile, can only be read not written to, on a small factory made chip on the memory board, contains all the instructions needed to boot a computer up.
von neumann architecture
what a general purpose computer is based on, CPU runs programs stored in memory, instructions + data stored in memory address.
Central Processing Unit (CPU)
Processes data and instructions, and controls the computer’s hardware.
Control Unit (CU)
Decodes instructions which are received from memory, executes instructions in the right order, and sends and receives signals from hardware.
Arithmetic Logic Unit (ALU)
Carries out logical (booleans), arithmetic, and shift (shifting binary) operations.
Memory Address Register (MAR)
Holds the address of the memory location where data/instructions are to be fetched/stored.
Memory Data Register (MDR)
Holds the data/instruction that has been fetched or will be stored in memory.
Current Instruction Register (CIR)
Holds the current instruction to be executed.
Program Counter (PC)
Register that holds the memory location address of the next instruction to be fetched, and increments after each instruction is fetched.
Accumulator (ACC)
Register that holds the results of calculations or operations carried out by the ALU.
Cache
Temporarily holds data/instructions that the CPU will likely reuse, as cache is faster to access than RAM.
Fetch-Decode-Execute Cycle
The address of the next instruction to be fetched is copied from the PC to the MAR. The PC increments. The instruction is copied from the MAR to the MDR, and then to the CIR. The CU decodes the instruction in the CIR, and then sends signals to the hardware that is needed. The instruction is executed by the components.
Clock speed
The number of fetch-execute cycles the CPU can do in a second, measured in Hertz (Hz).
CPU performance
Factors:
Clock speed
Number of cores
Cache size
Embedded system
Systems that are built into another device, with a limited range of functions, to control the device. They are usually small, with a single microprocessor, cheap, reliable, require little power, and have their system printed onto one board. Examples are a dishwasher, GPS and digital watch.