NIELIT BCC flashcards

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

Nyquist channel capacity

For a noiseless channel of bandwidth B hertz using M discrete signal levels, the maximum data rate is C = 2B times log base 2 of M, in bits per second.

Shannon capacity formula

For a channel of bandwidth B with signal-to-noise power ratio S/N, capacity is C = B log2(1 + S/N) bits per second. S/N must be a linear ratio, not decibels.

Decibel to linear ratio

Convert a power ratio in decibels to linear form using ratio = 10 raised to (dB divided by 10). Thus 20 dB equals 100 and 30 dB equals 1000.

Half-duplex transmission

A communication mode in which both stations can transmit but not at the same time. Walkie-talkies are a common example; full-duplex allows simultaneous two-way traffic.

Private IPv4 address ranges

Non-routable address blocks reserved for internal networks: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. Traffic using them needs NAT to reach the public Internet.

Usable hosts in a /24

A /24 IPv4 prefix contains 256 addresses. The all-zero host part is the network address and the all-ones host part is broadcast, leaving 254 usable host addresses.

Bits per QAM symbol

An M-ary modulation scheme carries log2(M) bits per symbol. 16-QAM carries 4 bits, 64-QAM carries 6 bits, and 256-QAM carries 8 bits per symbol.

Modulation purpose

Modulation shifts a baseband information signal onto a higher-frequency carrier so it suits the transmission medium, allows frequency multiplexing, and permits efficient antenna sizes.

Byte and binary prefixes

One byte equals 8 bits. Binary prefixes multiply by 1024: 1 KiB is 1024 bytes, 1 MiB is 1024 KiB, and 1 GiB is 1024 MiB.

Binary to decimal conversion

Sum each bit multiplied by 2 raised to its position, counting positions from 0 at the rightmost bit. For example 1101 equals 8+4+0+1 = 13.

Two's complement negation

To negate an n-bit number, invert every bit and add one. An n-bit signed value ranges from minus 2^(n-1) to 2^(n-1) minus 1.

Hexadecimal digit to bits

Each hexadecimal digit corresponds to exactly four binary bits, so F equals 1111 and A equals 1010. Two hex digits represent one byte.

RAM versus ROM

RAM is volatile read-write memory that loses its contents when power is removed. ROM is non-volatile and normally read-only, holding firmware such as the boot loader.

Full adder outputs

A full adder takes inputs A, B and carry-in. Sum equals A XOR B XOR carry-in, and carry-out is the majority of the three inputs.

ASCII code size

Standard ASCII is a 7-bit character code defining 128 code points. Extended ASCII uses 8 bits and defines 256 code points including accented and box-drawing characters.

Cache memory hierarchy

Fast small memory close to the CPU that stores recently used data. Order by increasing access time: registers, L1, L2, L3 cache, main RAM, then disk storage.

Absolute versus relative reference

In a spreadsheet, A1 is relative and shifts when copied. $A$1 is absolute and stays fixed. $A1 locks the column and A$1 locks the row.

COUNT versus COUNTA

COUNT returns the number of cells containing numeric values in a range. COUNTA counts all non-empty cells, including text and logical values.

Spreadsheet IF function

IF(condition, value_if_true, value_if_false) returns one of two results depending on whether the logical test evaluates to true or false.

Email Cc versus Bcc

Cc adds visible secondary recipients whose addresses all recipients can see. Bcc adds hidden recipients whose addresses are not disclosed to other recipients.

URL component order

A URL is written scheme://host:port/path?query#fragment. The scheme names the protocol, the host names the server, and the fragment identifies a location within the page.

HTTP status code classes

The first digit groups responses: 2xx success, 3xx redirection, 4xx client error such as 404, and 5xx server error such as 500.

Default HTTP and HTTPS ports

HTTP uses TCP port 80 by default and HTTPS uses TCP port 443. A non-default port must be stated explicitly in the URL after a colon.

Spreadsheet #### display

When a numeric or date result is wider than its column, the cell shows hash marks. Widening the column or reducing decimal places reveals the value.

Digital signature guarantees

A digital signature verifies the signer's identity, confirms the message was not altered, and prevents later denial of signing. It does not by itself hide the message content.

Symmetric versus asymmetric keys

Symmetric encryption uses one shared secret key and is fast, as in AES. Asymmetric encryption uses a public and private key pair, as in RSA, and is slower.

Cloud service models

IaaS provides virtualised infrastructure such as servers and storage. PaaS provides a managed runtime for deploying applications. SaaS provides a complete application over the network.

Blockchain hash chaining

Each block stores the cryptographic hash of the previous block, forming an append-only chain. Changing an earlier block invalidates all later hashes, making tampering detectable.

UPI payment interface

The Unified Payments Interface is an instant bank-to-bank payment system run by NPCI in India. A UPI ID takes the form username@bankhandle.

Phishing attack pattern

A social-engineering attack that impersonates a trusted party to trick users into revealing credentials or installing malware. Verifying the sender domain is a basic defence.

Multi-factor authentication

Authentication that combines two or more independent factor types, such as a password plus a one-time code, so a stolen password alone is insufficient to gain access.

Open-source software licence

Software whose source code is published under a licence such as GPL or MIT. The licence defines whether modified versions may be redistributed and under what terms.