WBCHSE HS Modern Computer Application cheat sheet

A computer system has input, CPU, main memory, secondary storage, and output units; the CPU contains the ALU, control unit, and registers.

The stored-program von Neumann model keeps instructions and data in the same addressable memory and executes them through fetch, decode, execute, and store stages.

Memory hierarchy from fastest and smallest to slowest and largest is registers, cache, main memory, and secondary storage; cache reduces average access time.

1 byte = 8 bits; 1 KB = 1024 bytes; 1 MB = 1024 KB; 1 GB = 1024 MB; 1 TB = 1024 GB.

CPU clock frequency f gives cycle time T = 1/f; at 2 GHz, one clock cycle lasts 0.5 ns.

RAM is volatile read/write working memory; ROM is non-volatile and retains firmware such as the bootstrap loader.

A bus is a shared set of lines; the address bus carries memory addresses, the data bus carries values, and the control bus carries read/write and timing signals.

An input device supplies data to the computer, an output device presents results, and a storage device retains data; a touchscreen serves as both input and output.

In base b, the value of digits d_n to d_0 is the sum of d_i multiplied by b^i; for example, 1011 in base 2 equals 8 + 0 + 2 + 1 = 11.

Decimal-to-base conversion repeatedly divides by the target base and reads remainders bottom-to-top; binary-to-octal groups 3 bits and binary-to-hex groups 4 bits from the right.

Binary addition rules: 0+0=0, 0+1=1, 1+0=1, and 1+1=10, writing 0 and carrying 1; subtraction uses a borrow of 2.

For n-bit two's complement, represent negative x by inverting x and adding 1; the range is -2^(n-1) to 2^(n-1)-1.

Boolean identities include X+0=X, X·1=X, X+1=1, X·0=0, X+X=X, X·X=X, X+X'=1, and X·X'=0.

De Morgan's theorems are (A+B)' = A'·B' and (A·B)' = A' + B'.

AND outputs 1 only when all inputs are 1; OR outputs 1 when any input is 1; XOR outputs 1 when the inputs differ.

A Karnaugh map groups 1s in blocks of 1, 2, 4, 8, or 16 adjacent cells, including wrap-around edges, to form a minimal sum-of-products expression.

System software includes the operating system, device drivers, and utilities; application software performs user-focused tasks such as word processing.

Operating-system functions include process management, memory management, file management, device management, and providing a user interface.

Process states usually include new, ready, running, waiting, and terminated; only one process per CPU core is running at a given instant.

Batch systems run jobs without interaction; time-sharing systems switch the CPU rapidly among users; real-time systems must meet specified deadlines.

Paging divides logical memory into fixed pages and physical memory into frames; segmentation divides memory into variable-length logical segments.

Virtual memory uses secondary storage to hold inactive pages, allowing programs larger than physical RAM through demand paging.

A file system organizes files in directories and tracks metadata such as name, size, location, and permissions.

BIOS or UEFI firmware performs the power-on self-test and starts the boot process by loading the operating-system loader.

A C program begins execution at main(); statements end with semicolons, and C is case-sensitive, so Total and total are different identifiers.

Common C types are int for integers, char for single characters, and float or double for real numbers; sizeof reports storage in bytes.

printf and scanf format specifiers include %d for int, %c for char, %f for float, %lf for double, and %s for strings.

Integer division truncates toward zero; the % remainder operator works only with integer operands.

if/else selects between alternatives; switch requires an integral controlling expression and uses break to prevent fall-through.

for, while, and do-while repeat statements; break exits the nearest loop or switch, while continue skips to the next iteration.

Arrays use zero-based indexing; a C string is a char array ending with a null character of value zero.

Functions have a return type, name, and parameter list; C passes arguments by value unless pointers are used.

Pointers store addresses: & gives a variable's address and * dereferences a pointer; malloc allocates heap memory and free releases it.

An array stores elements contiguously, giving O(1) access by index; inserting or deleting in the middle costs O(n) shifts.

A stack is LIFO: push adds at the top and pop removes from the top; applications include recursion, expression evaluation, and undo.

A queue is FIFO: enqueue adds at the rear and dequeue removes from the front; a circular queue reuses slots and avoids false overflow.

A linked list stores nodes containing data and a link; insertion at the head is O(1), but searching is O(n) because nodes are not indexed.

A binary tree has at most 2^h - 1 nodes at height h; level h contains at most 2^(h-1) nodes when the root is at level 1.

In a binary search tree, every left descendant is smaller and every right descendant is larger than the node; inorder traversal gives sorted output.

Tree traversals: preorder root-left-right, inorder left-root-right, postorder left-right-root, and level order breadth-first.

Linear search is O(n); binary search is O(log n) but requires a sorted array and direct access to the middle element.

Bubble, selection, and insertion sort average O(n^2); merge sort and quicksort average O(n log n), with quicksort worst case O(n^2).

A relation is a table with tuples as rows and attributes as columns; degree is the number of attributes and cardinality is the number of tuples.

A primary key uniquely identifies rows and cannot be NULL; a foreign key references a candidate key in another table and enforces referential integrity.

SQL DDL includes CREATE, ALTER, and DROP; DML includes SELECT, INSERT, UPDATE, and DELETE.

SELECT query clause order is SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY; HAVING filters groups after aggregation.

Aggregate functions COUNT, SUM, AVG, MIN, and MAX return one value per group; except for COUNT(*), they ignore NULL values.

INNER JOIN returns matching rows; LEFT JOIN keeps all left-table rows; RIGHT JOIN keeps all right-table rows; FULL JOIN keeps all rows.

Constraints include PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK, and DEFAULT; UNIQUE permits NULL in many SQL systems.

1NF requires atomic column values; 2NF removes partial dependencies on part of a composite key; 3NF removes transitive dependencies on non-key attributes.

DELETE removes selected rows and can be rolled back; TRUNCATE removes all rows quickly; DROP removes the table structure itself.

PAN, LAN, MAN, and WAN describe networks by increasing geographic scope; LANs usually use Ethernet or Wi-Fi.

Topologies: bus shares one backbone, star connects nodes to a central device, ring forms a closed loop, and mesh provides multiple paths.

OSI layers from bottom are physical, data link, network, transport, session, presentation, and application; TCP/IP uses network access, internet, transport, and application.

IPv4 uses 32-bit addresses in dotted decimal; IPv6 uses 128-bit addresses; private IPv4 ranges include 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.

TCP is connection-oriented and reliable; UDP is connectionless and does not guarantee delivery, making it suitable for live streaming and DNS queries.

Common ports: HTTP 80, HTTPS 443, FTP 20/21, SMTP 25, DNS 53, DHCP 67/68, POP3 110, and IMAP 143.

DNS maps domain names to IP addresses; DHCP assigns IP configuration automatically; HTTP transfers web resources between client and server.

A hub repeats signals to all ports, a switch forwards frames by MAC address, and a router forwards packets between networks by IP address.

Circuit switching reserves a dedicated path; packet switching divides data into packets that may travel different routes and be reassembled.

HTML elements use opening and closing tags and may have attributes; the head element holds metadata and the body element holds visible content.

CSS can be inline, internal in a style element, or external in a .css file; external style sheets are reused across pages.

The CSS box model consists of content, padding, border, and margin; width by default applies to content only unless box-sizing is border-box.

JavaScript runs in the browser to add behavior, respond to events, and modify the DOM; server-side code runs on the web server.

Multimedia combines text, graphics, audio, video, and animation; raster graphics use pixels, while vector graphics use paths.

JPEG is lossy and suited to photographs; PNG is lossless and supports transparency; GIF supports up to 256 colours and simple animation.

Common audio formats include MP3 and WAV; common video formats include MP4 and WebM; compression reduces file size for transmission.

HTTP is a request-response protocol; GET sends data in the URL, while POST sends data in the request body.

A URL contains scheme, host, optional port, path, query string, and fragment; the browser uses DNS and HTTP to retrieve the page.