Tamil Nadu HSE First Year Computer Science flashcards

38 cards. Read the term and the definition here. The deck at the top of this page is optional.

IPO cycle

Input-Process-Output: the fundamental model of computing in which data enters the system, is transformed by the processor under program control, and leaves as information, with storage supporting each stage.

Two's complement

A signed binary representation obtained by inverting all bits of a number and adding 1. For n bits the representable range is -2^(n-1) to 2^(n-1) - 1.

Universal gate

A gate from which every other logic function can be built. NAND and NOR are universal because each can produce NOT, AND and OR when wired appropriately.

De Morgan's theorems

Two Boolean identities: the complement of a sum equals the product of the complements, (A+B)' = A'B', and the complement of a product equals the sum of complements, (AB)' = A'+B'.

Half adder

A combinational circuit adding two single bits, producing Sum = A XOR B and Carry = A AND B. It cannot accept a carry-in, so full adders chain it for multi-bit addition.

Floor division operator

Python's // operator divides and rounds the result down to the nearest integer, so 7 // 2 is 3 and -7 // 2 is -4. The / operator always returns a float.

Indentation in Python

Leading whitespace defines statement blocks in Python instead of braces. Consistent indentation is syntactically required, and mixing tabs and spaces raises errors.

Loop else clause

Python allows an else block after for or while. It executes only when the loop ends normally, and is skipped when the loop exits through break.

Recursion base case

The condition in a recursive function that returns without calling itself again. Without a reachable base case, recursion continues until a RecursionError occurs.

List versus tuple

Lists are mutable, written with square brackets, and support item assignment. Tuples are immutable, written with parentheses, hashable when their items are, and usable as dictionary keys.

Dictionary get method

d.get(key, default) returns the value for a key, or the default when the key is absent. Unlike d[key], it never raises KeyError for missing keys.

Fetch-decode-execute cycle

The instruction cycle in which the CPU fetches the instruction addressed by the program counter, decodes its opcode, executes the operation, and stores any result.

Cache memory

A small, fast memory between the CPU and main memory that holds recently used instructions and data, exploiting locality of reference to reduce average access time.

Round robin scheduling

A preemptive CPU scheduling algorithm giving each ready process a fixed time quantum in turn. It is fair and responsive, but a very large quantum degenerates to FCFS.

Simplex transmission

A data communication mode in which signals travel in one direction only, such as keyboard-to-computer input or a television broadcast. Half duplex and full duplex allow two-way traffic.

Phishing

A social-engineering attack in which a fraudulent message impersonates a trusted entity to trick the recipient into revealing passwords, OTPs or card details, or into opening malicious links.

Digital signature

A cryptographic value created with the sender's private key and verified with the public key. It provides authentication, integrity and non-repudiation, but not confidentiality by itself.

Flowchart decision symbol

The diamond symbol in a flowchart. It represents a yes/no question, has one entry and two exits, and controls which branch of the algorithm executes next.

Binary search precondition

Binary search repeatedly halves the search interval and requires the data to be sorted. It runs in O(log n) comparisons, far fewer than linear search's O(n).

File open modes

Python open() modes: 'r' reads an existing file, 'w' writes and truncates, 'a' appends, and adding 'b' selects binary mode. Omitting the mode defaults to 'r'.

try except finally

Python's exception handling structure. try holds risky code, except handles named errors, else runs when none occurred, and finally always runs, typically for cleanup.

Module import forms

import math loads the module and uses math.sqrt; from math import sqrt binds the name directly; import math as m renames it. A package is a directory of modules with __init__.py.

random randint versus randrange

random.randint(a, b) returns an integer including both endpoints. random.randrange(start, stop, step) excludes stop, matching the behaviour of the range function.

Class and instance attributes

Class attributes are defined in the class body and shared by all instances. Instance attributes are set on self, usually in __init__, and belong to one object only.

Generator yield

A function containing yield returns a generator that produces values lazily, one per next() call, remembering its state. It is exhausted after one complete pass.

String slicing

s[start:stop:step] returns a new string from index start up to but excluding stop, taking every step-th character. Negative indices count from the end, and s[::-1] reverses.

String immutability

Strings cannot be changed after creation, so assigning to an index raises TypeError. All string methods return new strings, leaving the original object unchanged.

Set operations

Sets hold unique hashable items. Union (|), intersection (&), difference (-) and symmetric difference (^) combine them, and membership tests run in constant average time.

Shallow versus deep copy

A shallow copy duplicates only the outer container, so nested objects remain shared. copy.deepcopy recursively duplicates nested structures, giving a fully independent object.

Hexadecimal to binary

Each hexadecimal digit corresponds to exactly four binary bits, so D6 becomes 1101 0110. Conversion between binary, octal and hexadecimal passes through bit grouping.

Multiplexer

A combinational circuit with several data inputs, select lines and one output. The select lines choose which data input is routed to the output, earning the name data selector.

Truthy and falsy values

In Python conditions, zero, 0.0, empty strings, lists, tuples and dictionaries, None and False are falsy. Every other value, including negative numbers, is truthy.

TCP versus UDP

TCP is connection-oriented and reliable, acknowledging and retransmitting segments. UDP is connectionless, with no delivery guarantee, but has lower overhead for streaming and queries.

DNS

The Domain Name System translates human-readable domain names into IP addresses through a distributed hierarchy of name servers, letting browsers reach servers by name.

Ransomware

Malicious software that encrypts a victim's files or locks the system and demands payment for the key. Offline backups are the most reliable recovery defence.

Multi-factor authentication

Authentication requiring two or more independent factors, such as a password plus a one-time code or biometric. It limits damage when a password alone is stolen.

Cloud service models

IaaS provides virtual machines and storage, PaaS provides a managed runtime and tools for developers, and SaaS delivers complete applications over the internet on a subscription basis.

Blockchain

A distributed ledger of hash-linked blocks replicated across nodes, where consensus replaces a central authority. Records are append-only, making tampering detectable across the network.