PCI started with the first Pentium computers in the early 1990's. The most common PCI slot runs 32 bits of data at a time and operates at 33MHz, 5 volts, thus carrying a theoretical maximum transfer rate of 133MB/sec (actual transfer rates vary depending on hardware configuration but can be from 80MB/sec to 125MB/sec).

Two new common standards have emerged, one being 32 bits but 66MHz, thus doubling the theoretical bandwidth to 266MB/sec. The other is 64 bits at 66MHz with a theoretical bandwidth of 533MB/sec. These slots are typically backwards compatable to standard 33MHz 32bit PCI cards. These new PCI slots operate at 3.3 volts.