Computer Organization (IBCS SL; original broken)

original set in study hub broken

What is the CPU?

The Central Processing Unit — the central element of a computer system. It contains the circuitry necessary to fetch program instructions from RAM, decode them, and execute them.

What is the Control Unit (CU)?

A component of the CPU that loads and decodes commands, and directs the flow of data and the operation of the ALU.

What is the ALU?

The Arithmetic Logic Unit — performs all arithmetic operations (e.g. addition, subtraction) and logical operations (e.g. AND, OR). Sometimes called a "core"; dual-core means two ALUs for parallel processing.

What is the MAR?

The Memory Address Register — connected to the address bus. It holds the RAM address of the next instruction the CPU wants to fetch.

What is the MDR?

The Memory Data Register — connected to the data bus. It holds data to be written to RAM or data read from RAM. The MAR provides the address; the MDR holds the corresponding data.

What are buses in a computer system?

Connecting wires that link the CPU to other devices, carrying instructions to/from components. Usually integrated into the motherboard. Types: Data Bus, Control Bus, Address Bus.

What does the Data Bus do?

Links RAM to the CPU via the MDR — carries actual data values.

What does the Control Bus do?

Links RAM to the CPU via the CU — carries control signals.

What does the Address Bus do?

Links RAM to the CPU via the MAR — carries memory addresses.

What is RAM?

Random Access Memory — volatile primary memory that stores modules needed for applications, supports multitasking, and provides temporary storage for programs loaded since booting. Data is lost when power is off.

What is ROM?

Read Only Memory — non-volatile memory that contains the BIOS and startup operations. Data is retained when power is off and cannot be written to or changed.

What is Cache Memory?

A small, high-speed memory inside the CPU that holds frequently used data so the CPU needs to access the much slower RAM less often, resulting in faster processing speeds.

What are the steps of the Fetch-Decode-Execute cycle?

1. FETCH: PC points to next instruction; CU sends address to memory; instruction loaded into IR; PC incremented. 2. DECODE: CU reads and decodes instruction; identifies opcode and operands. 3. EXECUTE: ALU performs operations; results written back; status register updated. 4. REPEAT.

What is the Program Counter (PC)?

A register that holds the address of the next instruction to be executed. It is incremented after each fetch so the CPU knows where to fetch next.

What is the Instruction Register (IR)?

A register that holds the instruction currently being decoded and executed by the CPU.

What is an opcode?

The operation code part of an instruction — specifies what operation the CPU should perform (e.g. Load, Add, Halt).

What is an operand?

The data or memory address part of an instruction that the opcode acts upon.

What is the Status Register (Flags Register)?

A register updated after execution of an instruction. It records the outcome by setting flags such as zero, carry, and overflow.

What is persistent storage and why is it needed?

Storage that permanently retains data even when the computer is off. Needed because RAM is volatile — without it, all data would be lost on shutdown.

List the history of storage in order.

1. Selectron Tube (32-512 bytes) 2. Punch Cards 3. Punched Tape 4. Magnetic Drum Memory (~10 kB) 5. Hard Disk Drive (~5 MB in 1956, later 2.52 GB+)

What is the difference between primary and secondary storage?

Primary storage (RAM, Cache) is directly accessible by the CPU and is volatile. Secondary storage (Hard Drive) is non-volatile. Off-line storage (CD-RW, USB, Tape) is removable secondary storage.

What is an Operating System (OS)?

A group of computer programs that coordinates all activities among computer hardware devices. It is the first program loaded by the boot program and always remains in memory.

What are the 5 key functions of an Operating System?

1. User Interface (UI) 2. Memory Management 3. Peripheral Management 4. Multitasking 5. Security

What is a cold boot vs a warm boot?

Cold boot: turning on a computer that was completely off. Warm boot: using the OS to restart a computer that is already on.

What is a GUI?

Graphical User Interface — a user interface featuring icons, windows, and menus. Part of the WIMP model: Windows, Icons, Menus, Pointers.

What is a CLI?

Command Line Interface — requires the user to type text commands directly. Advantage: fast, low memory/CPU use. Disadvantage: requires detailed command knowledge; errors cause failure.

What is a NLI?

Natural Language Interface — allows the user to interact with the computer by speaking or writing in natural language.

What is a MBI?

Menu Based Interface — presents the user with a selection of options to choose from rather than requiring typed commands.

What is memory management in an OS?

The OS manages RAM by allocating/deallocating memory to processes, using virtual memory (disk space as extended RAM), and segmentation and paging for efficient use.

What is peripheral management in an OS?

The OS controls peripheral devices (keyboard, mouse, printer, etc.) using device drivers — software that acts as translators between hardware and the OS.

What is multitasking in an OS?

The OS allocates CPU time between programs based on time and priority. Each task gets a time slice. Higher-priority tasks get more or longer slices. Uses process scheduling and context switching.

What is security in an OS?

The OS prevents unauthorized access through usernames, passwords, access control, encryption, firewalls, and antivirus. It protects files from unauthorized reading or writing.

What is a Word Processor?

Application software for storing, manipulating, and formatting text. Functions: text editing, spell/grammar checking, inserting images/tables, saving in various formats. Examples: Google Docs, LibreOffice Writer.

What is a Spreadsheet application?

Software where data is arranged in rows and columns. Functions: organise data, perform calculations, create charts, use formulas. Examples: Google Sheets, LibreOffice Calc.

What is a DBMS?

Database Management System — software for creating and managing databases. Functions: data storage/retrieval/updating, query processing, data integrity, multi-user access. Examples: MySQL, PostgreSQL.

What is CAD software?

Computer-Aided Design software — used to create, modify, and optimise designs. Functions: 2D/3D modelling, technical drawings, stress/heat simulation, blueprint generation. Examples: AutoCAD, SolidWorks.

What is graphic processing software?

Software for manipulating visual images. Functions: edit images, create raster/vector graphics, apply filters/effects, work with layers. Examples: Adobe Photoshop, GIMP.

What is a bit?

The smallest unit of data a computer can store. Represented as either 1 (true) or 0 (false). Short for binary digit.

What is a nibble?

A group of 4 bits.

What is a byte?

A group of 8 bits. Example: 11101001. A single typed keyboard character takes up one byte of storage.

What is the denary (decimal) number system?

The base-10 number system using digits 0-9. Used in everyday life. Examples: 5, 24, 316, 8715.

What is hexadecimal?

A base-16 number system using digits 0-9 and letters A-F (A=10, B=11, C=12, D=13, E=14, F=15). Used in programming as it is easier to remember than binary and faster than denary.

How do you convert decimal to hexadecimal?

1. Convert the decimal number to 8-bit binary. 2. Split into two 4-bit groups. 3. Convert each 4-bit group to denary. 4. Replace any value 10-15 with its hex letter (A-F).

How do you convert binary to denary?

Assign place values (128, 64, 32, 16, 8, 4, 2, 1) left to right. Add up the place values where the bit is 1. Example: 01100101 = 64+32+4+1 = 101.

How do you convert hexadecimal to denary?

Convert each hex digit to its 4-bit binary equivalent, combine into an 8-bit binary number, then convert to denary. Example: 5F = 0101 1111 = 95.

What does the AND gate do?

Output is TRUE only when BOTH inputs A and B are TRUE. Truth table: (1,1)=1 (1,0)=0 (0,1)=0 (0,0)=0. Real-world example: Fire alarm — smoke AND heat both detected.

What does the OR gate do?

Output is TRUE when A is true, B is true, or BOTH are true. Truth table: (1,1)=1 (1,0)=1 (0,1)=1 (0,0)=0. Real-world example: Car interior light — either door open.

What does the NOT gate do?

Unary operator — output is the OPPOSITE of the input. Truth table: 1=0, 0=1. Real-world example: Microwave stops (0) when door is open (1).

What does the XOR gate do?

Exclusive OR — output is TRUE when either A or B is true, but NOT when both are true. Truth table: (1,1)=0 (1,0)=1 (0,1)=1 (0,0)=0. Real-world example: Two light switches in one corridor.

What does the NAND gate do?

NOT AND — output is TRUE when NOT both inputs are true (opposite of AND). Truth table: (1,1)=0 (1,0)=1 (0,1)=1 (0,0)=1. Real-world example: Security system disengages only when both correct code AND ID are scanned.

What does the NOR gate do?

NOT OR — output is TRUE only when NEITHER input is true (opposite of OR). Truth table: (1,1)=0 (1,0)=0 (0,1)=0 (0,0)=1. Real-world example: AC turns on only when both windows A and B are closed.

What is Q = NOT (A AND B) in logic gate form?

An AND gate takes inputs A and B, and its output feeds into a NOT gate to produce Q. Equivalent to a NAND gate. Written as: (A AND B)'

What is Q = NOT A NOR B in logic gate form?

Input A passes through a NOT gate, then NOT A and input B feed into a NOR gate to produce Q. Written as: NOT A NOR B.

What is Q = C AND (A OR B) in logic gate form?

Inputs A and B feed into an OR gate. The OR output and input C feed into an AND gate to produce Q. Written as: C AND (A OR B).

What are the WIMP components of a GUI?

Windows: rectangular areas where apps run. Icons: pictures representing apps or files. Menus: lists of commands/options. Pointers: moveable symbols (e.g. arrow cursor) for interacting with screen elements.

What is the difference between OS-provided and application-specific UI features?

OS-provided: standard elements like menu bars and buttons ensuring consistency across apps. Application-specific: customised icons, pictures, and unique functionalities defined by each individual app.