Computer Organization (IB HL CS)

CPU

• Central processing unit

• Uses arithmetic and logic operations to process input and output useful information

ALU

• Arithmetic logic unit

• Performs all basic arithmetic, logic, and I/O operations

CU

• Control unit

• Retrieves/decodes instructions for CPU

• Directs data flow for ALU

MAR

• Memory address register

• Connected to address bus

• Contains RAM address of the next instructions

MDR

• Memory data register

• Connected to data bus

• Holds data that will be written to/was read from RAM

CPU Diagram

RAM

• Random access memory

• Also known as primary memory

• General-purpose storage, can be overwritten

• Directly accessible by CPU

• Stored in binary

ROM

• Read only memory

• Stores instructions/data

• Cannot be overwritten

Address bus

• Connects MAR to ALU

Data bus

• Connects MDR to RAM

Differences between RAM and ROM

RAM is volatile memory used for temporary storage, while ROM is non-volatile memory that stores permanent instructions.

DRAM

• Dynamic RAM

• Preferred for the main RAM of a computer system

SRAM

• Static RAM

• Faster, more expensive

• A small amount is placed between RAM and processor

• AKA the cache

Cache memory vs RAM

Cache memory is a smaller, faster type of volatile memory located between the CPU and RAM, used to temporarily store frequently accessed data for quick access, whereas RAM provides larger temporary storage for active applications and data.

Machine instruction cycle

• Fetch: CPU sends address to primary memory through address bus. Data bus copies this address’ instruction and sends it to CU.

• Decode: CU decodes instructions and fetches required data from primary memory. Data’s addresses are placed into memory bus and data is received by CPU through data bus.

• Execute: CPU executes the instructions.

• Store: CPU stores the result of instructions in primary address through buses then checks for the next instruction.

Persistent storage

• AKA secondary memory

• Can be written to, is non-volatile

• Hard drive, USB, floppy disk, ZIP drive, etc.

Virutal memory

A memory management technique that uses disk space to extend RAM by swapping data in and out as needed, allowing for larger applications to run on limited physical memory.

• AKA using secondary memory as a backup for primary memory

Primary vs secondary memory

Primary = small amount, volatile, expensive, faster, directly accessed by CPU

Secondary = large amount, retains data when powered off, inaccessible by CPU

Operating system

• Provides a user interface

• Does memory management

• Does peripheral management

• Allows multitasking

• Provides security

Word processors

Programs for storing, manipulating, and formatting text-input from keyboard then providing a printout

Spreadsheets

Program to arrange data in rows/columns and can be manipulated for calculations

DBMS

• Database management systems

• Systematic way to create, retrieve, update, and manage data

CAD

Computer aided design

1 byte (B)

8 bits (b)

Negative binary

Decimal binary

Different data types take up more space

NAND, NOR

NOT and, NOT or

XOR

One or the other, but not both

Common symbols for logic gates