BSEH SS Computer Science flashcards

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

Von Neumann bottleneck

The limitation on throughput caused by the single shared bus between CPU and memory, since instructions and data cannot be transferred at the same time.

Cache memory

Small, fast memory between CPU and RAM that stores recently or frequently used data; L1 is smallest and fastest, L3 is largest and slowest.

Firmware and POST

Firmware such as BIOS or UEFI is stored in ROM and runs the power-on self-test, checking hardware before handing control to the bootloader.

Two's complement range

For n bits, two's complement represents values from negative two to the power n minus one up to two to the power n minus one, minus one.

Hexadecimal to binary

Each hexadecimal digit maps to exactly four binary bits, so 2F in hex becomes 0010 1111 in binary; grouping by four is the conversion rule.

Signed overflow condition

In two's complement addition, overflow occurs only when two operands of the same sign produce a result of the opposite sign.

UTF-8 encoding

A variable-length Unicode encoding using one to four bytes per character; ASCII characters use one byte, which makes it backward compatible with ASCII.

Process state transition

A process moves from new to ready, then running when scheduled, to waiting on I/O, back to ready, and finally terminated.

Absolute versus relative path

An absolute path starts at the root directory, while a relative path is resolved from the current working directory using dot and dot-dot.

Virtual memory and page fault

Virtual memory uses disk space to extend RAM; a page fault occurs when a referenced page is not in memory and must be loaded.

Deadlock four conditions

Deadlock requires mutual exclusion, hold and wait, no preemption and circular wait simultaneously; removing any one condition prevents deadlock.

Flowchart decision symbol

A diamond shape represents a decision in a flowchart; it has one entry and two exits, typically labelled yes and no.

While versus do-while

A while loop tests its condition before each iteration and may run zero times; a do-while tests after the body and runs at least once.

Dry run or desk check

Manually tracing a program's variables line by line using sample input to verify logic and find errors without executing the code on a computer.

Algorithm properties

A valid algorithm is finite, has definite unambiguous steps, produces output from input, and every step is effectively executable.

Floor division in Python

The double-slash operator returns the quotient rounded down to the nearest integer, so 7 // 2 gives 3 and -7 // 2 gives -4.

Python mutable versus immutable

Lists and dictionaries are mutable and can be changed in place; strings, tuples and numbers are immutable, so operations return new objects.

Python range function

range(start, stop, step) generates integers from start up to but excluding stop, advancing by step; range(5) yields 0,1,2,3,4.

Python with statement

The with statement opens a file as a context manager and closes it automatically when the block ends, even if an exception occurs.

Stack LIFO operations

A stack inserts and removes items at one end only, the top, so the last item pushed is the first popped; peek views the top without removing it.

Circular queue wrap-around

A circular queue reuses freed slots by computing the next index as rear plus one modulo the array size, avoiding wasted space.

Binary search precondition

Binary search requires the data to be sorted; it halves the search interval each step, giving logarithmic time complexity.

Primary versus foreign key

A primary key uniquely and non-nullably identifies each row; a foreign key is a column referencing another table's primary key to enforce referential integrity.

WHERE versus HAVING

WHERE filters individual rows before grouping, while HAVING filters groups after GROUP BY and typically tests aggregate results.

Third normal form

A table is in 3NF when it is in 2NF and has no transitive dependency, meaning non-key attributes depend only on the key.

TCP versus UDP

TCP is connection-oriented and reliable with acknowledgements and retransmission; UDP is connectionless, faster, and does not guarantee delivery or ordering.

DNS and DHCP roles

DNS translates domain names into IP addresses, while DHCP automatically assigns IP addresses and network settings to devices joining a network.

OSI transport layer

Layer four of the OSI model provides end-to-end delivery, segmentation, flow control and port addressing; TCP and UDP operate here.

HTML image alt attribute

The alt attribute on an img tag supplies alternative text shown when the image fails to load and read by screen readers.

CSS box model

Every element is a box made of content, padding, border and margin; width by default covers content only unless box-sizing is border-box.

Ransomware defence

Ransomware encrypts files and demands payment; offline or versioned backups, patching and restricted user privileges are the main defences.

Symmetric versus asymmetric encryption

Symmetric encryption uses one shared secret key for both encryption and decryption; asymmetric uses a public key to encrypt and a private key to decrypt.