OGE Informatics cheat sheet

Information is any data that reduces uncertainty; data become information when interpreted in context.

Informatics studies the structure, storage, processing and transmission of information, with or without computers.

Information properties: objectivity, reliability, completeness, relevance, value, clarity - subjective properties depend on the receiver.

Signals are continuous (analog) or discrete (digital); a discrete signal takes finitely many values from a finite alphabet.

Information processes: collection, storage, processing, transmission, and output of information.

A computer performs only four basic operations on data: input, storage, processing, output; control coordinates them.

Hardware is the physical devices; software is the set of programs controlling the hardware.

Bit is the smallest unit of data (0 or 1); a byte is 8 bits and can encode one of 256 values.

Powers of two: 2^10 = 1024 (K), 2^20 = 1 048 576 (M), 2^30 (G), 2^40 (T); in computing prefixes usually mean powers of 1024.

1 byte = 8 bits; 1 KB = 1024 B; 1 MB = 1024 KB; 1 GB = 1024 MB.

Binary to decimal: sum digit × 2^position, positions counted from 0 at the right. Decimal to binary: divide repeatedly by 2 and read remainders bottom-up.

Octal and hexadecimal convert via binary groups of 3 or 4 bits; hex digits are 0–9 and A–F.

Arithmetic in base p: addition carries when the digit sum reaches p; subtraction borrows p.

Number of different codes of length k over an alphabet of size n is n^k.

Hartley formula: N = 2^i, so one symbol carries i = log2 N bits when all N outcomes are equally likely.

Information volume of text = number of characters × bits per character (e.g. 8 bits for a one-byte encoding, 16 for Unicode).

Image volume = width × height × bits per pixel; sound volume = sampling rate × bit depth × time × channels.

A model is a substitute object preserving the properties essential for the task; models can be material or information (sign-based).

Model types: descriptive, verbal, mathematical, tabular, graphic, simulation; a model is never a complete copy of the object.

Algorithm properties: discreteness, determinacy (definiteness), finiteness (termination), mass character, and effectiveness.

Algorithm forms of representation: verbal, flowchart, pseudocode, program; a flowchart uses oval (start/end), parallelogram (input/output), rectangle (process), rhombus (condition).

Basic structures: linear (sequence), branching (if/else), loop (with precondition, postcondition, or with a counter).

Loop with counter executes the body exactly n times for a counter running from 1 to n inclusive.

Tracing rule: maintain a table of variable values after each step; a loop body is executed while the condition holds.

Variable is a named memory cell; its type determines allowed values and operations (integer, real, string, Boolean, character).

Assignment changes the variable's value; the right side is evaluated first, then stored in the left side.

Integer division div discards the fractional part; mod gives the remainder; for positive a and b, a = (a div b)·b + (a mod b).

Boolean operators: not (highest), and, or (lowest); comparison operators return True/False.

Conditional: if condition then statement else statement; the else branch runs only when the condition is False.

Loops: for i := a to b executes b−a+1 times when a ≤ b; while condition executes while the condition is True (check first).

Array indexing usually starts at 1 in school pseudocode; element access a[i], length n, last element a[n].

Swap of two variables requires a temporary variable: t := a; a := b; b := t.

Von Neumann architecture: CPU (ALU + control unit), memory, input/output devices; programs and data share memory.

CPU executes instructions in a cycle: fetch, decode, execute; clock speed measured in GHz, bit width in bits.

RAM is volatile and fast; ROM is non-volatile; long-term storage: HDD (magnetic) and SSD (flash).

Software classes: system (OS, drivers, utilities), application (editors, browsers, games), and programming tools.

The OS manages files, memory, devices and processes, and provides the user interface.

File name = proper name + extension; extension (e.g. .txt, .doc, .bmp, .exe) suggests the format and the program that opens it.

Full file path = logical drive letter + chain of folders + file name, e.g. C:\SCHOOL\INFO\test.txt; folders form a tree.

File attributes include name, size, creation date, read-only, hidden, system.

A computer network is a set of computers connected by communication channels for exchanging data; a node is any device on the network.

Topologies: star (central hub), bus (shared cable), ring (closed loop); local network (LAN) vs global network (WAN).

Server provides resources and services; client requests them; the client–server model underlies most Internet services.

IP address identifies a device (IPv4: four numbers 0–255); DNS translates a domain name into an IP address.

URL structure: protocol://server/ path /file, e.g. https://site.ru/page.html; http/https are web protocols.

Email address: mailbox@server; the @ separates user name from server name; email needs a mail client or web interface.

Internet services: WWW, email, file transfer (FTP), instant messaging, streaming; a browser requests pages via HTTP and renders HTML.

Data transfer volume = transfer rate × time; e.g. at 1024 bit/s a 2048-bit file takes 2 s.

Threats: malware (viruses, worms, trojans), phishing, spam, social engineering, unauthorized access.

Antivirus software detects and removes malware but must be updated; it cannot replace safe behaviour.

Strong password: length ≥ 8–12 characters, mix of letters, digits and symbols, not a dictionary word, unique per service.

Phishing signs: unexpected urgency, requests for passwords or card data, mismatched or look-alike domain names, suspicious attachments.

Personal data (name, address, phone, passport, health) must not be published openly; privacy settings limit visibility.

Safe rules: do not open unknown attachments, verify links before clicking, use HTTPS sites, log out on shared computers.

Backups protect data from loss (failure, ransomware); legal aspects include copyright and prohibition of software piracy.

Spreadsheet cell reference: column letter + row number (B3); absolute reference $B$3 does not change when copied, relative B3 does.

Formula starts with =; operators + − * / ^ and comparison; functions SUM, AVERAGE, MIN, MAX, COUNT, IF, ROUND.

Copying a formula shifts relative references by the same offset as the copy; $ fixes the row and/or column.

Chart types: bar/column for comparing categories, pie for parts of a whole, line for trends over time.

Text processing: character formatting vs paragraph formatting (alignment, indents, spacing); find/replace, spell check, tables.

Search query operators: AND (both terms), OR (either term), NOT (exclude), quotes for an exact phrase; AND narrows, OR broadens.

Database: table = records (rows) × fields (columns); key uniquely identifies a record; queries filter by condition, sort orders records.

Sorting changes the order of records; a filter/query selects records but keeps all fields of matching rows.