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Basic mouse today has 3 buttons: left, middle (wheel), right. Many mouses today have 5 buttons, by adding 2 extra buttons for the thumb. Usually for browser forward/backward.
But many gaming mouses sports 9 or more buttons. Why do you need it?
- 3 standard left/middle/right buttons.
- 2 buttons for browser back/forward.
- 2 buttons for prev/next tab. This is incredibly useful.
- 1 button for closing tab (【Ctrl+w】). Again, extremely useful.
That's 8 buttons already. To be luxurious, you'll also want:
- 2 button to switch window or workspace.
- 1 button to close window. (【Alt+F4】)
Then, there's desire. You desire:
- Side scroll wheel is useful. Saves you from scrolling side-to-side that's sometimes handy. Mouse makes count them as 2 buttons.
- Logitech's flywheel. This is actually critical in Linux, because X11 doesn't support accelerated scroll. Usually, there's a button to toggle this.
- Resolution switch. Usually, there are 2 buttons for this. This is quite important in some games. For example, in military combat games, when you snipe someone far away, reducing resolution helps aiming greatly. See picture here: Xah Combat Aim Radar.
Counting the Buttons: Practical vs Technical
Usually, mouse makers count all things that sends a signal. For example, they count 2 buttons for increase/decrease DPI resolution as programable buttons, and count mouse wheel left/right push as 2 more buttons. And, the standard left/middle/right are also counted as 3 buttons.
That's not a good way to count buttons if you are shopping, because, such buttons have default actions that you wouldn't want to change.
You should count only buttons that can be practically used for your customization.
Best Multi-Button Mouse
The best multi-buttons mouse is this:
Practically 7 extra buttons. Flywheel. Wireless, but rechargeable.
Second best is:
12 buttons on the side, like a keypad, but sculpted, so you can easily feel the right button. Wired. No flywheel.