teach me like i know nothing, COMPUTER SCIENCE 047... Flashcards

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Chapter 4

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Heading in the TERM2 revision worksheet that lists questions for Chapter 4. The document shows numbered items with placeholders labelled 'ANS' where students are expected to write answers, indicating a template-style revision sheet.

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Chapter 10

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Heading in the TERM2 revision worksheet corresponding to Chapter 10 content and questions. The sheet uses 'ANS' placeholders for responses, implying students must supply answers based on the syllabus topics.

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Binary conversion

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Methods to convert denary (decimal) numbers into binary include breaking the number into sums of powers of two or using successive division by two and reading remainders in reverse. For example, converting $59$ by either method yields the 8-bit binary $00111011$, illustrating both subtraction of powers of two and division-remainder techniques.

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Hexadecimal

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A base-$16$ number system using digits $0$–$9$ and letters $A$–$F$ (where $A=10$ to $F=15$). Each hex digit maps to four binary bits, making conversion between binary and hex straightforward; for example, binary $11011111$ converts to hex $DF$, and hex is commonly used in MAC addresses, IPv6 and HTML colour codes.

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Binary addition

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Binary addition follows the same carry rules as decimal addition but with base $2$, generating carries when sums exceed $1$. Adding two $8$-bit numbers can produce a ninth carry bit, indicating an overflow error because unsigned $8$-bit values are limited to $255$, so any result above $255$ cannot be stored in $8$ bits without overflow.

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Logical shift

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A logical shift moves all bits in a binary number left or right, inserting zeros into the vacated positions; left shifts multiply the value by $2$ for each shifted place and right shifts divide by $2$ (ignoring fractions). Excessive shifting can discard significant bits and cause data loss or zeroing when operating within a fixed bit width.

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Two's complement

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A binary representation for signed integers where the most significant bit indicates the sign ($1$ for negative, $0$ for positive) and negative numbers are formed by inverting bits and adding $1$. For example, an $8$-bit two's complement range is $-128$ to $+127$, and the format simplifies arithmetic and hardware implementation of subtraction.

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ASCII

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A character encoding standard using $7$-bit codes to represent basic Latin characters, digits and control codes, with an extended $8$-bit set to include additional symbols. ASCII is simple and compact but cannot represent the many characters required for worldwide languages.

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Unicode

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A comprehensive character encoding standard that supports a vast range of scripts and symbols from many languages, using variable-length encodings up to four bytes per character. Unicode enables internationalisation and consistent text representation across platforms and applications.

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Sampling rate

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The number of audio samples taken per second, measured in hertz (Hz), which determines how accurately an analogue sound wave is captured; higher sampling rates give better frequency representation. Increasing the sampling rate improves audio quality but also increases file size and processing requirements.

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Sampling resolution

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Also called bits per sample, sampling resolution is the number of bits used to record each audio sample and affects dynamic range and precision. Higher resolution (more bits) captures finer amplitude detail, improving quality but increasing file size proportionally.

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Pixel

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The smallest addressable element in a bitmap image, representing a single colour value at a specific position in a grid. Images are formed from many pixels arranged in rows and columns, and total detail depends on the number of pixels (resolution) and each pixel's colour depth.

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Color depth

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The number of bits used to represent the colour of a single pixel; with $n$ bits per pixel you can represent $2^{n}$ different colours. Higher colour depth produces more accurate and rich images but increases the amount of storage required per pixel.

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Image resolution

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The dimensions of an image given by its width and height in pixels, for example $4096 \times 3072$, where larger resolutions provide more detail. Higher resolution increases file size and demands more storage and bandwidth to transmit or display.

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Data units

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Digital information is measured in bits and bytes; one byte equals $8$ bits and larger units include kilobytes, megabytes, gigabytes and terabytes. There is a distinction between decimal (SI) prefixes and binary (IEC) measurements, which can cause differences in reported storage sizes.

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Run-Length Encoding

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A simple lossless compression technique that replaces sequences of repeated values with a single value and a count, reducing storage for data with long runs of identical elements. RLE is effective for simple images and texts with repetition but less effective for noisy or complex data.

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Lossy compression

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A compression approach that permanently removes some data to achieve much smaller file sizes, exploiting perceptual limitations (e.g., JPEG for images, MP3 for audio). While lossy formats greatly reduce storage and bandwidth needs, they lose fidelity and cannot be restored to the original bit-for-bit state.

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Bandwidth

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The maximum data transfer rate of a network link, typically measured in kilobits per second (kbps) or megabits per second (Mbps). Higher bandwidth allows more data to be transmitted per unit time, improving download and streaming performance subject to other factors like latency and congestion.

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Parity check

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An error-detection technique that adds a single parity bit to a data byte to make the count of $1$ bits either even (even parity) or odd (odd parity). Parity can detect single-bit errors but cannot locate or correct errors and fails to detect errors that flip two bits.

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Asymmetric encryption

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A cryptographic system using key pairs: a public key for encryption and a private key for decryption, enabling secure messages without sharing a secret key. For example, Jane generates a public/private key pair and gives Tom her public key so he can encrypt a confidential document that only Jane can decrypt with her private key; asymmetric encryption scales well for many senders and supports digital signatures.