ZIF is an acronym for "Zero Insertion Force". A normal integrated circuit socket requires the IC to be pushed into sprung contacts which then grip by friction. For an IC with hundreds of pins, the total insertion force can be very large (the equivalent of several kilograms), leading to a danger of damage to the device. To avoid this problem, the ZIF socket was invented. Before the IC is inserted, a lever or slider on the side of the socket is moved, pushing all the sprung contacts apart so that the IC can be inserted with very little force. The lever is then moved back, allowing the contacts to close and grip the pins of the IC. One alternative to ZIF sockets are slots in which the contacts are in a line.
ZIF sockets are used for expensive ICs such as microprocessors, which are likely to be upgraded or replaced several times during the lifetime of the socket. They are also used in chip-testing and programming equipment, when the same socket will be used to test or program hundreds of chips.
ZIF sockets are much more expensive than standard IC sockets, so they are only used where the latter are unsuitable.
By the mid 1990s, PCss were primarily using ZIF sockets for CPU's.