Computer Time Synchronization and Network Time Protocols

A comprehensive vocabulary review of computer timekeeping concepts, operating system time representations, clock deviations, and the hierarchical NTP architecture.

File Timestamping

The recording of the time when a file was created, modified, accessed, or otherwise changed.

Ticket Expiration

A security use of time in which authentication or access tickets become invalid after a defined time.

Time Zone

A local representation of time based on geographic or administrative location.

UTC

Coordinated Universal Time; a common reference time used across systems.

GMT

Greenwich Mean Time; often discussed alongside UTC as a common reference.

Zulu Time

Another term commonly used to represent UTC time.

Daylight Saving Time

A seasonal adjustment applied to local clock time in some regions.

UNIX Epoch

00:00:00 January 1, 1970.

UNIX Time

The number of seconds elapsed since the UNIX Epoch.

UNIX 2038 Problem

The condition where traditional UNIX time representations can overflow on January 19, 2038 if not corrected.

Real-Time Clock (RTC)

The hardware clock that keeps time in BIOS, continues running when the computer is powered off, and is notoriously inaccurate.

System Time

The time maintained by a process running inside the operating system, which depends on consistent processor timing.

PDC FSMO Role

The Windows Active Directory role that acts as the domain time authority to which domain members synchronize.

SNTP

Simple Network Time Protocol; a protocol where a single transaction sets the clock at that moment, allowing drift between synchronization events.

NTP

Network Time Protocol; a protocol designed to keep system clocks continuously synchronized and accurate using UTC and leap-second handling.

Marzullo's Algorithm

An algorithm referenced in the lecture that accounts for transmission duration when using time data.

Clock Skew

A difference between the local system clock and the reference clock.

Clock Drift

The gradual tendency of a clock to gain or lose time.

Drift File

A file used by NTP to record clock drift information so the system can better correct itself.

Stratum 0

A highly accurate underlying reference source, such as an atomic clock or GPS receiver, that is not normally client-facing.

Stratum 1

A time server directly connected to a Stratum 0 reference source that typically services other time servers rather than ordinary end clients.

Stratum 2

A time server that synchronizes to at least two Stratum 1 servers and may peer with other Stratum 2 servers.

Stratum 3

A time server that synchronizes to multiple Stratum 2 servers, may peer with other Stratum 3 servers, and commonly provides time to organizational clients.

NTP Stratum Rule

The rule stating that a machine is one stratum higher than the time server to which it synchronizes.

NTP Pool

A group of publicly available NTP servers that are geographically organized to theoretically reduce transmission delay.

NTP Timestamp

A 64-bit structure consisting of a 32-bit seconds field and a 32-bit fractional seconds field, reaching an accuracy of approximately 0.233 nanoseconds and wrapping every 136 years (next in 2036).