There are primarily three types of PCI slots that exist.
Most systems bought between 1995 and 2010 have a conventional PCI slot. Newer computers between 2003 and 2011 are more likely to have both conventional PCI and PCI-E (also known as PCI Express). Some may only have one or the other though. There are two types of PCI-E slots. A 1x slot and a 16x slot. 16x slots are compatible with 1x and 16x cards. 1x slots are not compatible with 16x slots.
To the left we show a 1x PCI-E card and to the right a conventional PCI card.
Some slimmer desktop computers (2000 on) require a "low profile" version of the above cards. The difference between these low profile cards is the bracket on them is shorter. This bracket measures about 3.118 inches (79.2 mm) as shown below.
