A-Level Computer Science - Advanced Analysis & Problem Solving

Front

Explain the precision loss incurred when subtracting two similar floating-point numbers (catastrophic cancellation).

Back

When two nearly equal floating-point numbers are subtracted, the most significant bits cancel out, leaving only the least significant bits which hold fewer bits of precision. Since floating-point normalization shifts the result, the relative error of these remaining small bits becomes massive. Example: In a low-precision system, (1.00001 - 1.00000) might yield 0.00000 due to insufficient mantissa bits to represent the tiny difference, resulting in a complete loss of significance.

Front

Differentiate between 'latency' and 'jitter' in network performance analysis.

Back

Latency is the total time taken for a data packet to travel from source to destination (Round Trip Time). Jitter is the variance in latency over time; it measures the inconsistency of packet arrival times. High latency causes delays, while high jitter causes irregular packet delivery, severely impacting real-time applications like VoIP or gaming where ordered, timely data processing is critical.

Front

Why is RLE (Run-Length Encoding) potentially ineffective for compressing analog-to-digital converted sound?

Back

RLE relies on consecutive repeated data values. Analog sound waves rarely produce long, exact repeating sequences when digitized because sampling captures continuous variations; adjacent samples usually differ slightly. Furthermore, high bit-depth audio increases the range of values, making exact repetition statistically improbable. Using RLE might even increase the file size if the run-length headers add overhead without matching runs of data.

Front

Analyze the security risk of 'Directory Traversal' in web applications.

Back

Directory Traversal (or Path Traversal) occurs when an attacker manipulates variables referencing files with '../' sequences to escape the web root folder and access restricted system directories. If an application does not sanitize user input (e.g., 'filename=../../etc/passwd'), the server may execute the request, exposing sensitive configuration files or source code. Mitigation involves strict input validation and using a whitelist of permitted files.

Front

Compare 'Circuit Switching' vs. 'Packet Switching' regarding bandwidth efficiency during silence.

Back

In Circuit Switching, a dedicated physical path is established for the duration of the session. If no data is transmitted (silence), the circuit remains open and occupies the bandwidth, leading to waste. In Packet Switching, data is divided into packets and sent only when necessary; resources are shared, and bandwidth is used only when actual packets are transmitted, making it significantly more efficient for bursty traffic but prone to congestion.