Computer Science: Data Representation, Architecture, and Systems

Comprehensive review flashcards covering data representation (binary, denary, hex, two's complement, sound, and graphics), data transmission, computer architecture (Von Neumann, FDE cycle, buses, memory), system software, and logic gates.

In the hexadecimal system, what are the denary equivalents for the letters A through F?

$A = 10$, $B = 11$, $C = 12$, $D = 13$, $E = 14$, and $F = 15$.

How is the binary number system defined, and what values are used to represent data in it?

The binary number system is a base $2$ number system based on the number $2$. Only the two values $0$ and $1$ can be used in this system to represent all values.

How does the heading method convert the denary number 142 into an 8-bit binary number?

By subtracting the largest possible power of $2$ successively until reaching $0$ ($142 - 128 = 14$, $14 - 8 = 6$, $6 - 4 = 2$, $2 - 2 = 0$), which produces the 8-bit binary number $10001110$.

When converting a denary number into binary, how can the final bit determine if the denary value is even or odd?

If the binary number ends in $0$, the denary number is an even number; if it ends in $1$, it is an odd number.

What is the equivalent denary value of the 8-bit binary number 11101110?

$128 + 64 + 32 + 8 + 4 + 2 = 238$.

How is the binary number 101111100001 converted into hexadecimal?

Split into groups of 4 bits from the right: $1011$ ($B$), $1110$ ($E$), and $0001$ ($1$), giving the hexadecimal value $BE1$.

What step must be taken when grouping a binary number into 4-bit nibbles for hex conversion if the leftmost group contains fewer than 4 bits?

Pad the leftmost group with leading $0$s (e.g., if the leftmost group is $10$, add two $0$s to make it $0010$).

How is the denary number 2004 converted into hexadecimal using the division method?

By successive division by $16$ until $0$ is reached: $2004 \div 16 = 125\text{ remainder } 4$, $125 \div 16 = 7\text{ remainder } 13\text{ (D)}$, $7 \div 16 = 0\text{ remainder } 7$. Reading remainders from bottom to top yields $7D4$.

How is the hexadecimal number 45A converted into denary?

Multiply each digit by its heading power: $(4 \times 256 = 1024)$, $(5 \times 16 = 80)$, and $(10 \times 1 = 10)$, then sum the totals: $1024 + 80 + 10 = 1114$.

What are four common uses of the hexadecimal system in computing?

Error codes, MAC addresses, IPv6 addresses, and HTML colour codes.

What is a Media Access Control (MAC) address?

A number which uniquely identifies a device on a network, taking the form $NN\text{-}NN\text{-}NN\text{-}DD\text{-}DD\text{-}DD$, where $NN$ is the manufacturer code and $DD$ is the device code.

What is bit overflow?

When a binary number is too large to fit in the available number of bits, causing the extra bit(s) to be lost.

What mathematical operations are performed by logical binary shifts to the left and to the right?

Each shift left multiplies the binary number by $2$, and each shift right divides the binary number by $2$.

How is two's complement calculated using the flipping bits method?

Starting from the right (least significant bit), keep all bits the same until the first $1$ is encountered; keep that $1$, and then invert/flip all remaining bits to the left.

How do ASCII, Extended ASCII, and Unicode differ in bit length and character capability?

ASCII uses 7-bit codes; Extended ASCII uses 8-bit codes (adding 128 codes for non-English and graphical characters); Unicode uses unique binary codes to support far more characters, languages (e.g., Chinese, Arabic, Japanese), and emojis.

What are the definitions of sampling rate and sample resolution in digital sound?

Sampling rate is the number of sound samples taken per second (in $\text{Hz}$). Sample resolution is the number of bits per sample.

In sound wave representation, what acoustic properties do amplitude and frequency correspond to?

Amplitude corresponds to loudness (higher amplitude = louder sound; lower amplitude = quieter sound). Frequency corresponds to pitch (higher frequency = higher-pitched sound; lower frequency = lower-pitched sound).

What are the benefits and drawbacks of using a higher sampling rate for sound?

Benefits: larger dynamic range, better sound quality, less sound distortion, and fewer sampling errors. Drawbacks: larger file size, takes longer to transmit/download, and requires greater processing power.

What formulas calculate the file size of mono and stereo sound files?

Mono: $\text{sample rate (in Hz)} \times \text{sample resolution (in bits)} \times \text{length of sample (in seconds)}$. Stereo: mono file size $\times 2$.

What is the formula used to calculate the file size of a bitmap image?

$\text{image resolution (in pixels)} \times \text{colour depth (in bits)}$.

What are the main distinctions between bitmap images and vector images?

Bitmap images are grids of individual pixels suitable for realistic photographs but pixelate when enlarged. Vector images are defined mathematically by shapes, lines, and curves, and can be scaled without losing quality.

How does Run-Length Encoding (RLE) compress data?

It is a lossless compression method that counts repeated consecutive data values and stores them as one value followed by the number of times it repeats (e.g., AAAAABBCCC becomes 5A 2B 3C).

How do lossy and lossless compression compare in data retention, file size, and typical formats?

Lossy compression permanently removes data to create a smaller file size but reduces quality (e.g., JPEG, MP3). Lossless compression reduces file size without losing any data, allowing the original to be restored with no loss of quality (e.g., PNG, ZIP).

What are the three components of a data packet in packet switching?

Header (contains source address, destination address, and packet number), Payload (contains the actual data being sent), and Trailer (contains error-checking data to detect transmission errors).

What is the difference between simplex, half-duplex, and full-duplex data transmission?

Simplex: data travels in one direction only. Half-duplex: data travels in both directions but not at the same time. Full-duplex: data travels in both directions at the same time.

What are the advantages and disadvantages of serial data transmission compared to parallel transmission?

Serial is cheaper (fewer wires), suited for long distances, and has less interference, but transmits only 1 bit at a time and can be slower. Parallel sends multiple bits at once over multiple wires (faster over short distances), but is more expensive, suffers from crosstalk/interference, and can suffer from skew.

How does fibre optic cable differ from copper cables (USB, coaxial, twisted pair) in transmission medium and properties?

Fibre optic carries data using light pulses through glass/plastic fibres; it provides very high speed over very long distances, is not affected by electrical interference, but has a high cost.

How does Automatic Repeat reQuest (ARQ) ensure accurate data transmission?

It uses acknowledgements and timeouts; if an error occurs or no acknowledgement is received within the timeout period, the packet is automatically resent.

What are the definitions and uses of checksum and check digit?

A checksum is a calculated value sent with data to check if network packets have been corrupted. A check digit is an extra digit added to a number (such as a barcode or ISBN) to verify it was entered correctly.

What is the key difference between symmetric and asymmetric encryption?

Symmetric encryption uses one single shared secret key to encrypt and decrypt data (faster). Asymmetric encryption uses two keys: a public key to encrypt and a private key to decrypt (slower, but provides secure communication without sharing private keys).

In asymmetric encryption, what distinct functions do the public key and private key perform?

The public key can be shared with anyone to encrypt messages for the owner or verify a digital signature. The private key is kept secret by the owner to decrypt received messages or create digital signatures.

What are the three main system buses in Von Neumann architecture and what are their directions?

Data Bus (carries data/instructions, bidirectional), Address Bus (carries memory addresses, unidirectional from CPU to memory), and Control Bus (carries control and timing signals like READ and WRITE).

What are the functions of the PC, MAR, MDR, and ACC registers in the CPU?

PC (Program Counter) holds the address of the next instruction; MAR (Memory Address Register) holds the address being accessed; MDR (Memory Data Register) holds data/instructions read from or written to memory; ACC (Accumulator) temporarily stores intermediate calculation results from the ALU.

What are the sequential steps of the Fetch–Decode–Execute cycle?

$1.$ PC holds next address $\rightarrow$ $2.$ Address copied to MAR $\rightarrow$ $3.$ PC incremented by $1$ $\rightarrow$ $4.$ Instruction fetched from memory $\rightarrow$ $5.$ Instruction copied to MDR $\rightarrow$ $6.$ Control Unit decodes instruction $\rightarrow$ $7.$ Instruction recognised using instruction set $\rightarrow$ $8.$ Instruction executed by ALU/CU $\rightarrow$ $9.$ Result stored in ACC/register $\rightarrow$ $10.$ Cycle repeats.

What are the definitions of system clock, cache, core, and clock speed?

System Clock generates pulses to synchronise components; Clock Speed controls instruction processing speed (measured in $\text{Hz}$/$\text{GHz}$); Cache is small, high-speed memory inside/near the CPU holding frequently used data; Core is an individual processing unit within a CPU capable of executing instructions.

What is an embedded system, and what is its operational sequence?

A computer system built into a larger device dedicated to one specific task. Its sequence is: Sensor $\rightarrow$ Signal/Data $\rightarrow$ Processor $\rightarrow$ Decision $\rightarrow$ Output signal $\rightarrow$ Actuator $\rightarrow$ Action $\rightarrow$ Feedback.

What are the specific functions of OMR, OCR, and MICR optical/magnetic reading hardware?

OMR (Optical Mark Recognition) detects marks in specific positions (e.g., exam answer sheets); OCR (Optical Character Recognition) converts scanned text into editable digital text; MICR (Magnetic Ink Character Recognition) reads characters printed in magnetic ink on bank cheques.

What are the differences between RAM and ROM?

RAM is volatile, temporary memory that holds programs and data currently in use and loses its contents without power. ROM is non-volatile, permanent memory that retains startup/firmware instructions when power is turned off.

What are the primary differences between SRAM and DRAM?

SRAM (Static RAM) uses flip-flops, does not require refreshing, is faster, more expensive, and is used for CPU cache. DRAM (Dynamic RAM) uses capacitors, requires regular refreshing, is slower, cheaper, has higher density, and is used for main memory.

What is virtual memory, and what are disk thrashing and the thrash point?

Virtual memory uses secondary storage to compensate for a physical RAM shortage. Disk thrashing is excessive data swapping in and out of an HDD causing high head movements. The thrash point is when program execution halts because the system spends all its time moving data rather than executing code.

What is the function of defragmentation software on a hard disk drive (HDD)?

It reorganises fragmented file pieces to store them in contiguous locations and organises free space, reducing read/write head movement and improving file access speed.

How does an interrupt signal get processed by the CPU?

CPU completes current instruction $\rightarrow$ saves current state/registers $\rightarrow$ identifies interrupt and priority $\rightarrow$ executes corresponding Interrupt Service Routine (ISR) $\rightarrow$ restores previous state $\rightarrow$ resumes original program.

What are the differences between a compiler and an interpreter?

A compiler translates the entire high-level program into machine code at once to produce an executable file before execution (executes faster). An interpreter translates and executes high-level instructions one by one (executes slower, but provides immediate step-by-step error reporting).

Which logic gate is shown in this diagram, and what is its truth table output condition?

NOT gate. The output $X$ is $1$ if input $A$ is $0$. Logic notation: $X = \text{NOT } A$; Boolean algebra: $X = \overline{A}$.

Which logic gate is shown in this diagram, and what is its truth table output condition?

AND gate. The output $X$ is $1$ only if both inputs $A$ and $B$ are $1$. Logic notation: $X = A \text{ AND } B$; Boolean algebra: $X = A \cdot B$.

Which logic gate is shown in this diagram, and what is its truth table output condition?

OR gate. The output $X$ is $1$ if either input $A$ or $B$, or both, are $1$. Logic notation: $X = A \text{ OR } B$; Boolean algebra: $X = A + B$.

Which logic gate is shown in this diagram, and what is its truth table output condition?

NAND gate. The output $X$ is $1$ if input $A$ and input $B$ are NOT both $1$. Logic notation: $X = A \text{ NAND } B$; Boolean algebra: $X = \overline{A \cdot B}$.

Which logic gate is shown in this diagram, and what is its truth table output condition?

NOR gate. The output $X$ is $1$ if neither input $A$ nor input $B$ is $1$. Logic notation: $X = A \text{ NOR } B$; Boolean algebra: $X = \overline{A + B}$.

Which logic gate is shown in this diagram, and what is its truth table output condition?

XOR gate. The output $X$ is $1$ if (input $A$ is $1$ and input $B$ is $0$) OR (input $A$ is $0$ and input $B$ is $1$). Logic notation: $X = A \text{ XOR } B$; Boolean algebra: $X = (A \cdot \overline{B}) + (\overline{A} \cdot B)$.