NIELIT ECC flashcards

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

Hexadecimal digit weight

Each hexadecimal digit represents four binary bits, so a byte is written as exactly two hex digits ranging 00 to FF, covering decimal 0 to 255.

Two's complement range

For n bits, signed two's complement spans −2^(n−1) through +2^(n−1) − 1. An 8-bit signed byte therefore covers −128 to +127.

Universal logic gates

NAND and NOR are called universal because either one alone can implement AND, OR and NOT, and therefore any Boolean function, without other gate types.

De Morgan's theorems

The complement of a product equals the sum of complements, and the complement of a sum equals the product of complements: (A·B)′ = A′+B′ and (A+B)′ = A′·B′.

XOR gate behaviour

The exclusive-OR output is 1 only when the two inputs differ. It acts as a controlled inverter and as a parity generator for odd-parity checks.

Karnaugh map grouping rule

Adjacent cells differing in one variable may be grouped in sizes of 1, 2, 4, 8 and so on. Larger groups yield simpler product terms with fewer literals.

JK flip-flop toggle state

When both J and K inputs are high, the JK flip-flop toggles: the next output is the complement of the present output, removing the invalid state of the SR flip-flop.

D flip-flop function

The D flip-flop transfers the value on its data input to the output at the active clock edge, giving a one-bit storage element used in registers and shift registers.

Multiplexer versus demultiplexer

A multiplexer selects one of many inputs onto a single line using select bits; a demultiplexer routes one input to one of many outputs. Both are combinational circuits.

Half adder outputs

A half adder adds two bits and produces Sum = A⊕B and Carry = A·B. A full adder adds a carry-in and is built from two half adders plus an OR gate.

Ripple versus synchronous counter

In a ripple counter each flip-flop clocks the next, accumulating propagation delay; in a synchronous counter all flip-flops share one clock, so outputs change together.

Shannon channel capacity

Capacity in bits per second equals bandwidth times log base 2 of (1 + signal-to-noise ratio as a power ratio), giving the maximum error-free data rate.

Nyquist sampling theorem

A band-limited signal must be sampled at more than twice its highest frequency component to be reconstructed without aliasing; the minimum rate is 2B samples per second.

SNR in decibels

Signal-to-noise ratio in decibels equals ten times the base-10 logarithm of the signal power divided by the noise power, both measured in the same units.

AM versus FM

Amplitude modulation varies carrier amplitude and is prone to noise; frequency modulation varies carrier frequency and offers better noise immunity at the cost of wider bandwidth.

QAM bits per symbol

Quadrature amplitude modulation combines amplitude and phase states. The number of bits per symbol equals log base 2 of the constellation size, so 16-QAM carries 4 bits.

OSI reference model layers

Seven layers from bottom: physical, data link, network, transport, session, presentation, application. Each layer provides services to the layer directly above it.

TCP versus UDP

TCP is connection-oriented with acknowledgements, sequencing and retransmission, giving reliable delivery. UDP is connectionless with low overhead, used for streaming and DNS queries.

IPv4 address classes

Class A starts with 0 (1–126), Class B with 10 (128–191), Class C with 110 (192–223). Class D (224–239) is multicast and Class E is reserved.

Private IPv4 ranges

Non-routable private blocks are 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Address translation typically maps these to a public address at the gateway.

Subnet mask function

A subnet mask has network bits set to 1 and host bits set to 0. A /24 mask 255.255.255.0 leaves 8 host bits, giving 254 usable host addresses.

MAC address structure

A 48-bit hardware address written as six hexadecimal octets. The first three octets identify the manufacturer (OUI) and the last three are assigned per interface.

Circuit versus packet switching

Circuit switching reserves a dedicated path for the whole session, as in telephony. Packet switching sends independently routed chunks that share links, as in IP networks.

Modem function

A modem performs modulation, converting digital data to an analog carrier for transmission, and demodulation, recovering digital data from the received analog signal.

Optical fibre advantage

Fibre carries data as light through a glass core, giving very high bandwidth, immunity to electromagnetic interference, low attenuation and no electrical crosstalk between strands.

Twisted pair cable

Two insulated copper conductors twisted together to cancel induced noise. Unshielded twisted pair is graded into categories, with Cat 5e and Cat 6 used for Ethernet.

Hamming code error correction

Redundant parity bits are placed at power-of-two positions. The number of parity bits r must satisfy 2^r ≥ m + r + 1 for m data bits.

Parity bit limitation

A single parity bit detects any odd number of bit errors but cannot detect an even number of errors, and it cannot locate or correct the error.

CRC principle

Cyclic redundancy check treats data as a polynomial, divides it by a generator polynomial using modulo-2 arithmetic, and appends the remainder as check bits.

Cache memory locality

Cache exploits temporal locality (recently used data reused soon) and spatial locality (nearby addresses used soon) to reduce average access time below main memory latency.

RISC versus CISC

RISC uses a small set of fixed-length simple instructions with many registers and pipelining. CISC offers complex variable-length instructions that may take multiple cycles.

RAM versus ROM

RAM is volatile read-write memory losing contents on power loss, used for working data. ROM is non-volatile and retains programmed contents, used for firmware and boot code.