IB Computer Science Paper 1 Topic 2

Components in the CPU

* Control Unit (CU)
* Arithmetic Logic Unit (ALU)
* Memory Address Register (MAR)
* Memory Data Register (MDR)
* Address Bus
* Data Bus

Arithmetic Logic Unit (ALU)

Performs all basic arithmetic and logical operations

Control Unit (CU)

* Obtains data from memory and decodes it into instructions
* Coordinates all the units of the computer

Memory Address Register (MAR)

* Holds the memory of the address data to be used by the ALU
* Holds address of where processed data will need to be stored

Memory Data Register (MDR)

* Holds the data to be used by the ALU
* Holds a copy of the contents of the memory to be transported to other components of the CPU

Address Bus

* Connects MAR to primary memory (RAM)

Data Bus

* Connects MDR and primary memory (RAM)

Two types of primary memory

Random Access Memory (RAM) and Read Only Memory (ROM)

Random Access Memory (RAM)

* Stores data and instructions currently in use - can be overwritten
* Volatile - whenever power is lost its memory is wiped
* Can be written to

Read Only Memory (ROM)

* Stores permanent instructions and data - info is embedded cannot be overwritten
* Non-volatile
* Much smaller than ROM
* Holds the Basic Input / Output System (BIOS)

Cache

* Stores frequently used instructions
* Is used to save time in accessing the RAM, as can be accessed faster than the RAM
* Situated between RAM and CPU, so closer to CPU
* Very small
* Static

Components of the machine instruction cycle

Fetch, decode, execute

Fetch

* CPU sends address from MAR of instruction through the address bus to the primary memory (RAM)
* Instruction in that particular address is sent through the data bus to the CU, stored in MDR

Decode

* CU decodes instruction, fetches any required data from the primary memory

Execute

* ALU executes instruction

Store

* The results of the executed instruction are stored in the accumulator

Secondary memory

* Relatively slow memory that can be written to
* Non-volatile
* Hard drives, USB sticks, Floppy disk

Operating system

Set of software that controls computer’s hardware resources and provide services for programs

Roles of an operating system

* Peripheral communication - communicating directly with hardware (keyboards, mice, printers)
* Memory management - manages how memory is used by applications, ensures one doesn’t interfere with the memory of another
* Data management - accessing and storing data
* Security

Benefits / execution of memory management

* Allocates and deallocates specific sections of memory to each process
* Ensures that a program has sufficient memory to run
* Ensures that the memory assigned to one program is not overwritten

How colour can be represented in a computer

* Split into three components (e.g RGB), and each component is given a specific number of bytes