Gigabyte (GB)

Represents a measurement unit for the storage capacity, equivalent with 1 million bytes. Although it's generally rounded at 1 million, one gigabyte actually contains 1,073,741,824 bytes or 1024 Megabytes.

GPS

Global Positioning System – the term defines the technology used for determining a set of geographical coordinates with the help of a system of artificial satellites that orbit around the Earth. The GPS system includes 2 major components: the satellites (launched, controlled and managed by the US Department of Defense), and the GPS receivers (either standalone, or included in various mobile devices). The GPS technology allows said receivers to determine their own geographical position (latitude, longitude and altitude) by comparing the signals broadcast by several satellites via microwaves. The GPS system is used mainly for navigation purposes, but also for surveying and mapping tasks In the same time, the global positioning system provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks.

GPS Receiver

It's the electronic device (usually portable) used for receiving the microwave broadcasts transmitted by the satellites from the GPS system. In order to be able to constantly determine their position (latitude, longitude and altitude), the GPS receivers measure the distance towards at least three satellites (although the most advanced devices of this type can receive up to 20 or even 24 satellites in parallel). This is achieved by measuring the time delay between the transmission and the reception of each GPS microwave signal, because the value of the signal's speed is a constant (the speed of light). After determining the relative position with respect to the three satellites, the receiver can compute its own position, via a trilateration process. Moreover, the devices track more satellites than they're actually required to, due to the fact that they need to permanently correct their own clock errors with the help of the satellites' atomic clocks.

GPS Satellite

represents the space vehicle used within the GPS system for determining a receiver's coordinates. The 31 GPS satellites currently in service rotate around the Earth at an altitude of around 20,200 kilometers (12,600 miles) and have an orbital radius of 26,600 km. Each satellite orbits the Earth at least twice each day, which means that it passes over the same location on Earth once 24 hours. The satellite's orbits are established in such a manner as to allow at least six satellites to always be within line of sight from almost everywhere on Earth's surface, thus allowing for an optimum functioning of the GPS system.

GSM

Global System for Mobile Communications – is the most widespread mobile communications system in the world. It is formed out of a cellular-type radio network, the receivers/transmitters (mobile handsets) connecting to the closest available cell. The GSM networks operate in 4 different frequency ranges: 850,900,1800 and 1900 Mhz, although in certain areas (Scandinavia) there are still some networks that operate on the 400-450 Mhz frequencies. The main reason behind the success of the GSM standard is represented by the fact that it assures digital quality voice calls, associated communication methods (SMS), as well as the possibility to carry out various data transfers (EDGE, GPRS). The first GSM network has been launched in Finland, in 1991, by a company called Radiolinja.