HD is the term used to differentiate the systems that generate, transmit or support HD content (High Definition) with those of standard definition or low definition (SD).

HD resolutions are usually at least 1280 x 720 pixels by taking the ratio "width x height". Being the height, 720 pixels, which make high resolution.

4G is the next generation of technology that the International Telecommunication Union has created for transferring data via the Internet. The speed is 100 MB/s downstream and 50 MB/s upstream, with a bandwidth of 20 MHz. The idea that used to wield the great value of 4G format that society is consuming more video and heavy images and this will make the mobile phone supports it. A continuación show you a small graphic comparison between 3G and 4G in the most common uses computer-related.

VDC would be the abbreviation for Volt Direct Current which translated would volts direct current. The idea of ??this type is unidirectional current to the load. Direct current is normally produced by batteries, thermocouples, solar cells and a dynamo electric machine type. The direct current can flow in conductors such as wires, but may also flow through semiconductors, insulators ... In the image: 1 - current per pulse 2 - Direct Current (DC) 3 - Alternating Current (AC) 4 - Variable Current