Quadra was the name used by Apple Inc. for most of its Macintosh computers built around the Motorola 68040 CPU. The first of these were the Macintosh Quadra 700 and 900, both introduced in 1991 with a CPU speed of 25 MHz. The former was a compact model using the same case as the Macintosh IIci, with a PDS expansion slot, while the latter was a new tower case with five NuBus expansion slots plus one PDS slot.
The latter was replaced in 1992 with the Macintosh Quadra 950, with a CPU speed of 33 MHz. The line was joined by a number of "800-series" machines in a new mid-sized case, starting with the Macintosh Quadra 800, and the "600-series" pizza-box desktop cases with the Macintosh Quadra 610.
In 1993 the Quadra AV series was released, consisting of the 800-series Macintosh Quadra 840AV and the 600-series Macintosh Quadra 660AV, at 40 MHz and 25 MHz respectively. Both included an ATT DSP and S-Video and composite input and output ports for video, as well as CD-quality microphone and audio output ports. The AV models also introduced speech software known as MacinTalk Pro and allowed the computer to be controlled through the microphone. However all of these features were poorly supported in software, and DSP was not installed in later AV Macs.
The Quadra name was also used for the successors to the Macintosh Centris models that briefly existed during 1993. Centris was a "mid-range" series of systems between the Quadra on the high end and the LC on the low end, but it was later decided that there were too many product lines and the name was dropped. Just to add to the confusion, several machines of this era were also sold as Performas.
The last use of the name appeared to be for the Macintosh Quadra 630, which was a variation on the Macintosh LC 630 using a "full" Motorola 68040 instead of the LC's 68LC040, and introduced together with it in 1994. The 630 was the first Mac to use to an IDE based drive bus for the internal hard disk drive, whereas all earlier machines had used SCSI.