Topic 2 Flashcards
Computer Organization
What is the Centeral Processing Unit
Component of a computer system which interprets/ processes and executes program instructions.
What is the ALU?
Performs arithmetic and logical calculations/operations
What is the Control Unit?
It handles the loading of new commands into the CPU and the decoding of these commands.
Also, it directs the data flow and the operation of the ALU. Decodes the instructions fetched from memory
What are registers?
1) Small, very fast circuits that temporarily store values from calculations or instructions inside the CPU.
2) Hold small amounts of data needed as part of the fetch-execute cycle
What are buses?
Buses - Components within the CPU and wider computer system are connected by buses
A bus is a set of parallel wires through which data/signals are transmitted from one component to
another
There are 3 types of bus:
- Address - unidirectional, carries location data (addresses), data is written to/read from
- Data - bidirectional, carries data or instructions
- Control - bidirectional, carries commands and control signals to tell components when they should be receiving reads or writes etc..
What is primary memory? (3)
1) Primary memory is the computer’s main memory and stores data temporarily.
2) Primary memory is the only storage that is directly accessible by the CPU
3) The primary memory stores instructions.
What is RAM? (6)
1) This memory can be written to, and instructions and data can be loaded into it.
2) Contains the data and instructions the computer has loaded since starting up and everything the user has opened or loaded.
3) The RAM is where instructions, and values are stored at runtime
4) The RAM can be accessed a lot faster than secondary storage
5) It is Volatile - All data and instructions are lost when the power is turned off (volatile).
6) Allows storage and random access to data and instructions
7) High speed
8) RAM is smaller than secondary memory
What is ROM?
ROM – Read Only Memory - Read only memory
1) You cannot delete, or edit
2) Permanent memory - All the system instructions are stored in ROM.
3) The operating system gets saved on ROM.
4) ROM is a non-volatile memory that permanently stores instructions for your computer
5) It stores BIOS
What is the fetch execute cycle?
The basic operation of a computer is called the ‘fetch-execute’
cycle (also called the ‘machine cycle’).
The computer fetches the instruction from its memory and then executes it.
This is done repeatedly from when the computer is booted up to when it is shut down.
Memory Address Register (4)
1) Holds the memory address of where data or instructions are to be fetched from memory.
2) MAR is connected to the address bus.
3) MAR contains a memory address.
4) MAR’s sole function is to store the address in memory (RAM or ROM) that the CPU needs to access, whether for fetching instructions or data.
Steps in the fetch execute cycle
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Fetch
PC
The address of the next instruction is copied onto the MAR from PC
RAM
The Data is fetched using the address from the MAR and sent to the MDR
MDR
The instruction is stored in the
MDR which is then copied into the CIR
CIR
Decode
CU
Execute
ALU
The instructions are then sent to the CU which makes changes to the ALU. The ALU then executes the instruction and stores them in the Accumulator if needed.
Store
ACCUMALTOR
The
Accumulator stores the results of the executed instruction.
What is the purpose of BIOS?
BIOS (basic input/output system) is the program a computer’s microprocessor uses to start the computer system after it is powered on.
Outline one difference between ASCIl and UNICODE representation.
1) ASCII uses 7 bit + check bit / parity bit = 8 bits;
Unicode extends it to 8/16/32 bit;
UNICODE has bigger character set so requires more disk space;
2) ASCII encodes only 128 characters by assigning numbers;
Unicode may use different and more sophisticated representation;
3) ASCII American English alphabet+ control;
Unicode tries to include all possible existing alphabets;
What is Cache Memory? (3)
1) Small and high speed memory, it is faster than RAM as it is coser to the CPU.
2) It stores the most frequently used data and instructions so CPU has to access the slower RAM less often and performance speeds up.
3) It stores frequently accessed data and instructions to reduce the time the cpu spends waiting for data from the slower main memory.
Secondary Memory (persistent memory) (2+examples)
1) Computer memory that is non-volatile, persistent and not immediately accessible by a computer or processor.
2) Secondary storage devices are used to store data and programs that are not currently being used or accessed by the computer’s CPU (Central Processing Unit).
3) Examples - Hard disk drives (HDD) , Solid-state drives (SSD), Optical discs (CD, DVD, Blu-ray), USB flash drives
Why do we need storage?
There would be no physical place to store data memory. The RAM has space for memory but that is only meant to be for short-term memory, not long-term. The hard drive or SSD drive is where the computer stores it’s physical data. You always need at least some storage device, otherwise, the computer has no place .
What is a program counter
Holds the memory address of the next instructions to be executed
Memory Data Register (4)
1) MDR stores the data or instruction which has been fetched from memory.
2) MDR temporarily holds the data that is being transferred to or from the memory.
3) MDR is connected to the data bus.
4) MDR holds data that will be written to the RAM or
that was read from RAM.
Relationship between MAR & MDR
The MAR gives the address the data of the MDR will be read from or written to.
Current Instruction Register
Stores the instruction the CPU is currently decoding or executing
Accumalator
Stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU)
What are buses (2)
1) Components within the CPU and wider computer system are connected by buses
2) A bus is a set of parallel wires through which data/signals are transmitted from one component to
another
Types of buses (3)
1) Data bus (links RAM to CPU via MDR)
2) Control bus (links RAM to CPU via CU)
3) Memory bus (links RAM to CPU via MAR)
