Topic 2 - Computer Organization

CPU

CPU

(Central Processing Unit) Using the Control unit, arithmetic logic unit and RAM it performs the machine instruction cycle to execute machine code instructions in a program.

ALU

Arithmetic and Logic Unit - part of CPU that executes the instruction through mathematical calculations and logical decisions

Register

A register is a file that acts as a slot in the CU of the CPU where you can store bits.

CU

Control Unit - part of the CPU which performs decoding. obtains the data/instructions from memory; interprets/decodes the instruction into commands/signals. It then controls the transfer of data and instructions among other units of the CPU. Also manages/coordinates all the units of the computer (MAR, ALU, MDR, etc.)

MAR

Memory Address Register - is a register(memory location) in the CPU that stores the address of the next instruction to be read/written to from RAM

MDR

Memory Data Register - is a register(memory location) in the CPU that holds the data which is most recently read from the RAM.

RAM

volatile memory that is erased when power is switched off. It has fast access speed (faster than hard drives/secondary memory). The data/instructions of programs currently running can be read from and written to RAM. Memory in RAM can be overwritten and it's size is limited.

Secondary Memory

A type of memory that allows a user to store data and programs for as long as desired, in, for example, a hard disk drive. \n \n Non-volatile, persistent storage that is significantly slower than primary memory.

Machine Execution Cycle

Fetch, Decode, Execute, Store

Fetch

Address bus is used to specify the address to which obtain instructions from. Address register contains the address necessary. Processors transfers instructiosn through data bus from RAM. Data register now contains necessary data.

Decode

Control unit obtains instructions from register and decodes them into commands/steps. Controls and transfer data to ALU for execution.

Execute

ALU executes instructions using data in data register.

Store

Once execution is finished, address bus is used to set writing address. Processors uses data bus to transfer data to the appropriate address in primary or secondary memory. Data is then stored and next instruction is fetched.

Bus

collection of electrical conduits carrying bytes of information

Address Bus

a physical connection that transfers data to-from the CPU. When the processor needs to fetch an instruction from memory it uses the address bus to specify the physical address block it needs to access. The data is then transfered by the data bus. One the results of the execution are ready, the process uses the address bus to set the writing address. The data bus then transfers the data to memory locations.

Data Bus

bus is defined as a physical connection that transfers data to-from the CPU. The data bus enable a processor to communicate with the primary memory. When fetching an instruction the computer processor places the data on the data bus, which carries the data to the processor. once the instruction is executed, the processor dfates data to be written to emmory on the data bus to be carried to primary/secondary memory.

Cache

memory that is located between the processor and RAM. It is fast, more smaller in capacity, than RAM. It is used to save time in accessing RAM.

Operating System (OS)

Software used to control the computer and its peripheral equipment.

Features of Software Applications

Toolbars, menus, dialogues, and GUI's

Range of Different Software Applications

Word Processor \n Spreadsheet \n Database \n Email \n Database management systems \n Web Browser \n CAD

bit

single binary value, 1 or 0

byte

8 bits = 1 byte, every letter, number, or special character on the keyboard is represented by 1 byte

Binary

The binary number system is base 2, using only bit values 0 and 1.

Hexadecimal

A base-16 number system that uses sixteen distinct symbols 0-9 and A-F to represent numbers from 0 to 15.

Ways data is represented

Colors: RGB or Hexadecimal \n Text: ASCII or UTF-8

ROM

permanent memory that is used by the computer to save instructions and data that won't change and can't be overwritten. It is used to store instructions that the computer needs in order to boot up.

Persistent storage

Persistent storage is needed to store data in a non-volatile device during and after the running of a program.

Operating Systems functions

1. Memory allocation

2. Memory availability management

3. Virtual Memory Management

4. Security

Memory Allocation by OS

The operating system assigns block of memory to the program when a program requests a block of memory. When the program no longer needs the data in previously allocated memory blocks, they become available for reassignment.

Memory availability management by OS

Ensures the availability of adequate memory from data structures/objects of each running program at all times by allocating the memory portions to programs after freeing the space of the computer memory.

Virtual memory management by OS

The memory management units in the OS uses virtual memory which provides secondary memory for a program that doesn't have enough space in RAM for execution. After execution of a program memory is reallocated/freed

Security provided by OS

OS prevent programs from accessing data/instructions without appropriate permissions.