# tabs on pci card connector

[John A Grandy]

does anyone know why some pci card slot-connectors have 2 tabs (1 large, 1
small) and some have 3 tabs (1 small, 1 large, 1 small) ... ?

 

[Bob Willard]

does anyone know why some pci card slot-connectors have 2 tabs (1 large, 1
small) and some have 3 tabs (1 small, 1 large, 1 small) ... ?

There are two different answers:

1. PCI cards use keying (cut-outs in the connector area) to
distinguish between 5V cards, 3.3V cards, and Universal cards.
This prevents cards of one type being plugged into slots of
an incompatible type.

2. Some PCI cards use a 64-bit bus, and some PCI cards only use
a 32-bit bus (or use 32 bits of a 64-bit bus). The pins for
the extra 32 bits are on an additional connector piece
(tab, as you call it).

If you want details, google for a PCI spec. But for most users,
you only need to match the card type with the slot type as per the
above two issues.