Argument on keyboards with the max number of keys presses being registered is a technical limitation confined to keyboards.
Keyboards were never ever meant for gaming. At least not the hard core gaming we do.
There is a stat for keyboards known as** Key Rollover**. Key Roll Over is how many keys can be pressed and still be understood by the keyboards on keyboard encoder and the computers.This number can be anywhere from 1 key plus 1 modifier to 6 keys + all modifiers, to Infinite keys + all modifiers.
The MAX for USB Keyboards set by the the limitations of the keyboard protocols are 6 character/ fuction keys + all 4 modifiers.Or a Rollover of 6 keys+ 4 Modifiers.
A Modiffier key would be Shift, Alt, Crtl and Super (known on a Windows PC as the Windows Key, the Apple Key on a Mac). There are other modifiers but they are unused on a modern Windows/ Linux / Mac OS. (such as the Fn key)
If you keyboard has a round ps/2 plug (not to be confused with Sony’s PS2), depending on the quality of the encoder inside there no limit to the key roll over. Often called Infinite or N Key Roll Over, although the actual limit is 120-140 keys plus all 4 modifiers (the number of keys on a keyboard). Each key is scanned individually and not by any technological limits.
It also depends how the interface works too.
USB works on a Polling protocol, where the Keyboard must wait its turn till the Computer us ready for its input (time measured in a few Micro seconds)
This isn’t a issue of they keyboard is the Sole device on a USB Port. But it becomes a issue if used with a hub connected to other devices.
ps/2 works on a interrupt protocol. Pretty much it tell the computer you have no choice but accept this input or else.
For PC gaming, a PS/2 keyboard encoder with n key rollover or a USB Gaming HID device encoder. USB Keyboards are limited to 6 keys.
If you ask me, Unless you are part of the (very) Old-school MAME crowd, there no reason to use a keyboard encoder for a stick. Go for a USB HID Game controller (human interface device). They function with out drivers and are plug and play.
A Gaming HID USB device include but not limited to Cthulhu, Dual Strike, Paewang ect…
Some online stores that cater to the MAME crown have encoders that can carry the functions of both players on a PC as a USB gaming HID device.
Technically Xbox 360 controllers are not HID devices, since they are not Driver-less. But they still are a better option than a keyboard encoder.