Section One: Components of a computer Flashcards
Chapter One : Processor components
What is the CPU?
Central processing unit
The internal hardware component of the computer that is responsible for executing the instructions of programs
Chapter One : Processor components
What is included in the CPU?
- Control unit
- Buses
- Arithmetic logic unit(ALU)
- Dedicated registers
Chapter One : Processor components
What is a control Unit?
Handles the flow of data and instructions.
It includes all the inputs and outputs required of the CPU.
It also sends commands to the ALU and directs operations on memory.
The Immediate Access Store is the internal memory of the CPU including its registers and caches.
Chapter One : Processor components
What are buses?
A ‘bus’ consists of a number of parallel wires (conductors). And each wire handles a single data bit, so it is either at logic 1 (true) or logic 0 (false).
When the CPU wishes to access a particular main memory location, it sends this address to memory on the address bus. The data in that location is then returned to the CPU on the data bus. Control signals are sent along the control bus.
Chapter One : Processor components
What is a control bus?
The CPU needs to receive and send control information between other parts of the computer. For example there is a control line between the power supply and the CPU that tells the CPU to boot up once the power supply is steady enough. There is another control line that handles external interrupts and so on. Collectively these lines are called the control bus.
Chapter One : Processor components
What is a data bus?
The data bus in a standard (Von Neumann) CPU handles both data and instructions. The purpose of the data bus is to allow data to pass from one area to another. The one above is shifting data between the CPU and main memory. But there are also internal data buses to move information around.
The width of the bus determines how many bits the CPU can handle at once.
Typical widths are 8 bit, 16 bit, 32 bit and 64 bits.
Chapter One : Processor components
What is an address bus?
The CPU must be able to define where the content of the data bus is going to or coming from. And to do this, there is a separate bus called the ‘Address Bus’. The CPU places the location of the data (or instruction) on the address bus. Just like the data bus, each wire in the address bus is a single data bit, so it is at logic 1 or logic 0.
The width of the address bus determines how many locations it can access. For example a 16 bit address bus can access up to 216 locations or 65,536 locations.
Chapter One : Processor components
What is an arithmetic logic unit?
An ALU performs basic arithmetic and logic operations.
Examples of arithmetic operations are addition, subtraction, multiplication, and division.
Examples of logic operations are comparisons of values such as NOT, AND, and OR.
Chapter One : Processor components
What types of Registers are there?
- Accumulator
- Program counter(PC)
- Current instruction register(CIR)
- Memory address register (MAR)
- Memory data register (MDR)
Chapter One : Processor components
What is the role of an accumulator?
A type of register for short-term, intermediate storage of arithmetic and logic data in a computer’s CPU
Chapter One : Processor components
What is the role of an Program counter?
Holds the address of the next instruction to be executed.
Chapter One : Processor components
What is the role of current instruction register(CIR)?
Holds the current instruction being executed, divided into operand and opcode.
Chapter One : Processor components
What is the role of memory address register(MAR)?
Holds the address of the memory location from which data (or an instruction) is to be fetched or to which data is to be written.
Chapter One : Processor components
What is the role of memory data register(MDR)?
Used to temporarily store the data read from or written to memory. It is also sometimes known as the memory buffer register.
Chapter One : Processor components
What is the Fetch-decode-execute cycle?
The sequence of operations involved in executing an instruction can be divided into three phases – fetching, decoding and executing it. This cycle is repeated over and over as each instruction of the program is executed.
Chapter One : Processor components
How the registers are used in the Fetch-Execute cycle?
(Fetch phase)
1. The address of the next instruction is copied from the program counter (PC) to the memory address register (MAR).
2. The instruction held at that address is copied to the memory data register (MDR). Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction.
3. The contents of the MDR are copied to the current instruction register (CIR).
(Decode phase)
4. The instruction held in the CIR is decoded. The instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it. The operand holds either:
- the address of the data to be used with the operation, which is then copied to the MAR, or
- the actual data to be operated on, which will be copied to the MDR
- the data to be operated on may be passed to the ALU/accumulator
(Execute phase)
5. The appropriate instruction/opcode is carried out on the operand.
Chapter Two: Processor performance
What are the factors affecting processor performance?
- Clock speed
- The number of cores, or duplicate processors, linked together on a single chip
- The amount and type of cache memory
Chapter Two: Processor performance
What is Clock speed?
Clock speed is the number of cycles that are performed by the CPU per second. It is measured in hertz — one hertz is one cycle per second
Chapter Two: Processor performance
What are number of core?
The number of cores indicates the number of processing units in a computer. Nowadays, computers can contain two (dual-core), four (quad-core), six, twelve, or even more cores.
Chapter Two: Processor performance
What is cache memory?
Cache memory is a very fast type of memory, which is used to store the instructions and data that are used most commonly. When the CPU has a data request, it checks the cache first, before it accesses the much slower main memory. Therefore, increasing the cache size can increase the chance of retrieving the required data faster, which, in turn, improves the CPU performance.
Adding larger sizes of cache to a CPU makes it more expensive to produce, so there is always a trade-off between cost and speed.
Chapter Two: Processor performance
What is pipelining?
Pipelining is the process of completing the fetch, decode, and execute cycles of three separate instructions simultaneously, holding appropriate data in a buffer in close proximity to the CPU until it’s required. While one instruction is being executed, another can be decoded and another fetched.
Chapter Two: Processor performance
What is an address bus?
Used to transport memory addresses, specifying where data is to be sent to or retrieved from. Increasing the width of the address bus increases the range of addresses that it can specify, hence increasing the computer’s amount of addressable memory
Chapter Two: Processor performance
What is a data bus?
A computer’s data bus sends data and instructions to and from the different components of the computer system. Increasing the width of the data bus increases the volume of data that can be transferred over the bus at any one time.
Chapter Three: Types of processer
What is the von Neumann machine?
Von Neumann architecture was first published by John von Neumann in 1945.
His computer architecture design consists of a Control Unit, Arithmetic and Logic Unit (ALU), Memory Unit, Registers and Inputs/Outputs.
Von Neumann architecture is based on the stored-program computer concept, where instruction data and program data are stored in the same memory. This design is still used in most computers produced today.
Chapter Three: Types of processer
What is the harvard architecture?
Harvard Architecture is the computer architecture that contains separate storage and separate buses (signal path) for instruction and data. It was basically developed to overcome the bottleneck of Von Neumann Architecture. The main advantage of having separate buses for instruction and data is that the CPU can access instructions and read/write data at the same time.
Chapter Three: Types of processer
Von Neumann machine Vs harvard architecture
Von Neumann machine
- It is ancient computer architecture based on stored program computer concept.
- Same physical memory address is used for instructions and data.
- There is common bus for data and instruction transfer.
- Two clock cycles are required to execute single instruction.
- It is cheaper in cost.
- CPU can not access instructions and read/write at the same time.
- It is used in personal computers and small computers.
Harvard architecture
- It is modern computer architecture based on Harvard Mark I relay based model.
- Separate physical memory address is used for instructions and data.
- Separate buses are used for transferring data and instruction.
- An instruction is executed in a single cycle.
- It is costly than Von Neumann Architecture.
- CPU can access instructions and read/write at the same time.
- It is used in micro controllers and signal processing
Chapter Three: Types of processer
What are contemporary processor architecture?
Contemporary Processing Contemporary processors use a combination of Harvard and Von Neumann architecture. Von Neumann is used when working with data and instructions in main memory, but uses Harvard architecture to divide the cache into instruction cache and data cache.
