Lets start with what a gamer peripheral is or better yet ARE since its not just one thing in general. It can be anything that enhances the gamers experience that is connected to the computer to enhance the gamers experience. Since this enhances your Gaming experience I call it the Gamers Gear. this ranges all over the place from the mouse and keyboard to headsets and game pads.
While not of this stuff is really needed much of it is desired do to it enhancing the way you can play.
Lets take the Mouse for instance it has a simple enough design. It allows the pointer to move around and normally has 3 buttons one of which is also the scroll wheel. It gets the job done, how ever if your a gamer and you get a gaming mouse you will have many more buttons allowing you to play at a much higher rate than those who do not.
The same thing goes with Keyboards, some keyboards are designed to allow gamers to have additional options that a normal keyboard just will not allow. making some things much easier. Example of this would be a key combo of 3 different keys, put onto a macro key for a single push button.
Headsets while not differing much on what there used for, have different things there better for some are really good for music while others are better at voip (stuff like Skype, Teamspeak, Ventrillo). Then there are all types of usb or using the jacks. the there is the range of frequencies, craziness.
Keypads are one of the more useful gamer peripherals out there it acts as the keyboard does (just not the typing) and puts all the essential buttons in the reach of one hand, which includes movement, along with a bunch of extra buttons for easy programing for things you want want to do more quickly.
Controllers or Gamepads, These are great for many games, and especially great for games that where designed for a console, or even for friends who are use to console games and haven't got the hang of keyboard and mouse. Many games will have a option for this peripheral, and since its the standered Xbox/ PlayStation type controller most players will have no problem using them
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