BGCSE Computer Studies 0597 cheat sheet

CPU cycle: fetch → decode → execute → store; clock speed in hertz sets cycles per second.

Von Neumann architecture stores instructions and data in the same main memory, sharing one bus.

RAM is volatile and holds running programs; ROM is non-volatile and holds firmware such as the bootstrap loader.

Cache sits between CPU and RAM: L1 fastest and smallest, L3 slower and larger; hit rate raises performance.

Primary storage is directly addressable by the CPU; secondary storage (HDD, SSD, optical) needs transfer into RAM first.

Input devices convert physical signals to digital data; output devices convert digital data to human-perceivable form.

SSD uses flash memory with no moving parts: faster access, lower power, but limited write cycles and higher cost per GB.

Buses carry data, addresses and control signals; wider data bus and higher clock rate increase throughput.

System software (OS, utilities, drivers) manages hardware; application software performs user tasks.

OS functions: memory management, process scheduling, file management, device management, user interface, security.

Compilers translate the whole source program before execution; interpreters translate and execute line by line.

Assemblers convert assembly language to machine code; each mnemonic maps to one machine instruction.

Utility programs include backup, antivirus, disk defragmentation, compression and file management tools.

Open source software publishes source code for modification; proprietary software restricts copying and modification by licence.

GUI uses windows, icons, menus and pointers; CLI requires typed commands and suits automation.

Device drivers are OS-specific translators between the OS and a particular hardware peripheral.

1 byte = 8 bits; 1 KiB = 1024 bytes; 1 MiB = 1024 KiB; 1 GiB = 1024 MiB.

Binary place values double leftwards: 128 64 32 16 8 4 2 1 for one byte.

Hex digit = 4 bits; two hex digits = 1 byte, so hex is shorthand for binary.

Denary to binary: repeatedly divide by 2 and read remainders bottom to top.

Unsigned 8-bit range 0–255; two's complement 8-bit range −128 to +127.

Two's complement: invert all bits and add 1 to negate a value.

ASCII uses 7 bits (128 characters); Unicode uses variable encoding to cover all world scripts.

Bitmap image size in bits = width × height × colour depth; sound file size = sample rate × bit depth × duration × channels.

LAN covers one site; WAN spans large distances and typically uses third-party links.

Star topology: central switch, single cable failure isolated, but switch failure halts the network.

Bus topology: one backbone cable, terminators at both ends, collisions rise with traffic.

TCP is connection-oriented and retransmits lost packets; UDP is connectionless with no delivery guarantee.

IP addresses identify hosts; DNS resolves domain names to IP addresses.

Circuit switching reserves a path for the whole call; packet switching routes independent packets by best path.

Protocols: HTTP/HTTPS for web, SMTP send mail, POP3/IMAP retrieve mail, FTP transfer files.

Bandwidth is capacity in bits per second; latency is delay; both affect perceived network speed.

The Internet is the global network of networks; the World Wide Web is a service running over it via HTTP.

URL parts: protocol, domain name, path, and optional query string.

Search engine stages: crawling, indexing, ranking; Boolean operators AND, OR, NOT narrow or widen results.

Cloud computing delivers IaaS, PaaS or SaaS over a network; data resides on remote servers.

IoT connects embedded sensors and actuators to networks, generating continuous data streams.

AI systems learn patterns from data; machine learning outputs depend on training data quality.

Blockchain is a distributed append-only ledger where each block hashes the previous block.

Virtual reality immerses the user in a simulated environment; augmented reality overlays digital content on the real world.

Flat file: one table, data duplication; relational database: linked tables sharing key fields.

Primary key uniquely identifies a record; foreign key is a primary key stored in another table to create a link.

Field = column (attribute); record = row (entity instance); table = file of related records.

Data types constrain input: text, number, date/time, currency, Boolean, and lookup.

Validation checks data on entry (range, type, presence, length); verification confirms accuracy (double entry, visual check).

DBMS functions: storage, querying, updating, reporting, concurrency and access control.

SQL SELECT retrieves fields from tables; WHERE filters rows; ORDER BY sorts results.

Data redundancy wastes space and risks inconsistency; normalisation splits data to remove repetition.

Three control structures: sequence, selection (IF/CASE), iteration (FOR count-controlled, WHILE condition-controlled).

Algorithm design tools: pseudocode and flowcharts; flowchart symbols: oval terminal, parallelogram input/output, rectangle process, diamond decision.

Variable holds a changeable value; constant is fixed once assigned.

Data types: integer, real, Boolean, character, string; type mismatch causes runtime or logic errors.

Syntax error breaks language rules and prevents compilation; logic error runs but gives wrong output.

Test data: normal, boundary and erroneous; dry run or trace table follows variable values step by step.

Subprogram (procedure or function) groups reusable code; parameters pass data, return values send results back.

Linear search checks each item in turn; binary search halves a sorted list each step and is faster on large data.

SDLC stages: analysis, design, development, testing, implementation, maintenance.

Fact-finding methods: interview, questionnaire, observation, document analysis, record sampling.

Feasibility checks: technical, economic, legal, operational, schedule.

DFD shows processes, data stores, external entities and data flows; context diagram is level 0.

Implementation methods: direct changeover, parallel running, phased conversion, pilot running.

Requirement types: functional (what the system does) and non-functional (performance, usability, security).

Entity relationship diagram shows entities, attributes and relationships with cardinality (1:1, 1:M, M:N).

Documentation: user documentation for operation, technical documentation for maintenance and future developers.

Malware types: virus (attaches to files), worm (self-replicates over networks), trojan (disguised), spyware, ransomware.

Phishing deceives users into revealing credentials; pharming redirects to fake sites via DNS or host file changes.

Encryption converts plaintext to ciphertext with a key; symmetric uses one key, asymmetric uses a public/private pair.

Firewall filters traffic by rules; proxy server intermediates requests; VPN encrypts traffic over public networks.

Authentication factors: something known (password), something held (token), something inherent (biometric).

Backup protects availability; antivirus detects known signatures; patching closes known vulnerabilities.

Copyright protects original works; software licence terms define permitted copying and installation.

Data protection principles: collect lawfully for stated purposes, keep accurate and secure, retain no longer than needed.

Automation raises productivity and can displace jobs while creating roles in maintenance and data work.

Teleworking reduces commuting but blurs work boundaries and needs reliable connectivity.

Digital divide separates those with access, skills and affordability from those without.

E-commerce lowers overheads and widens markets but raises concerns over fraud and delivery costs.

Social media enables rapid sharing but spreads misinformation and can reduce face-to-face contact.

ICT in banking enables mobile payments and online transfers but increases exposure to fraud.

Rapid hardware change creates e-waste; recycling and responsible disposal reduce environmental harm.

Health and safety: repetitive strain injury, eye strain and back pain are addressed by ergonomic furniture, breaks and correct posture.