The new PCI v2.3 specification is the first major upgrade to "Conventional PCI" since PCI v2.2 was released in December 1998. It is an evolutionary change that makes a significant step in migrating the PCI bus from the original 5 volt signaling to 3.3 volt signaling. Like PCI v2.2, the new specification supports two system board add-in card connectors for both the 3.3 volt and 5 volt signaling environments. However, PCI v2.3 does not support 5 volt-keyed add-in cards, which are now "non-compliant" with the PCI v2.3 specification. PCI v2.3 continues to support the Universal-keyed and 3.3 volt-keyed add-in cards. The Universal card is capable of detecting the signaling environment in use and adapting itself to that environment. By always using 3.3 volt output signals and having 5 volt-tolerant inputs, the Universal card can be plugged into both types of PCI slots (including PCI-X slots). This change is particularly important to adapter card vendors who must adopt PCI v2.3 to remain compliant and compatible with the most current version of the PCI local bus specification.