PS/2 is the connector used since IBM Personal System/2 to connect mouses and keyboards to popular computers.

it has largely replaced usage of older DE-9 (aka serial port) for those devices, and is mostly replaced with USB on modern devices. However, due to it's simplicity compered to USB, it's still popular in hobbyist OS and hardware development, as a USB HID driver is much more complex than a PS/2 driver.

%25width=200px lfloat%25 Attach:PS2.svg

||border=1 class="sortable simpletable"

||# Pin ||# Description (single) ||# Description double ||

|| 1 || data || data (keyboard) || 

|| 2 || not connected || data (mouse) || 

|| 3 || ground || ground ||

|| 4 || +5v || +5v ||

|| 5 || clock || clock (keyboard) ||

|| 6 || not connected || clock (mouse) ||

note maximum recommended amount of current over vcc is 100mA, but it's also possible to go over 275mA.

in PS/2, like serial mouse and unlike USB, devices sends information to system using interrupts, 

which means device sends a signal for change made to cpu, however in USB, system pulls changes done by device

every once in a while.

[more info](/http://www.burtonsys.com/ps2_chapweske.htm)