Macintosh Quadra

The Quadra series of Macintosh computers was launched by Apple Computer in 1991 as the company's high-end professional-grade machines, designed around the Motorola 68040 processor. It replaced the Macintosh II series and was succeeded by the PowerPC-based Power Macintosh series in 1994.

History
The Macintosh Quadra 700 and 900 were introduced in October 1991 as the first flagship models with a CPU speed of 25 MHz. The Quadra 700 was a compact model that used a similar case design as the Macintosh IIci, but with two NuBus slots. The Quadra 900 was introduced a new tower case design with five NuBus expansion slots. Both the 700 and 900 featured a new processor direct slot (PDS) designed for the 68040 processor.

The latter was replaced in 1992 with the Macintosh Quadra 950, with a CPU speed of 33 MHz. The line was joined by the Macintosh Quadra 800 in a smaller mid-sized case, and the Macintosh Quadra 610 in a flat pizza-box desktop case.

Centris
For a short time in 1993, Apple marketed Centris computers as a mid-range brand in between the high-end Quadra line and the entry-level LC line. Three models were released under the Centris brand: the Macintosh Centris 610, 650, and 660AV. Only the 660AV used the full 68040 processor. The 610 and 650 used the cheaper 68LC040, which lacked a floating-point unit (FPU). Due to confusion among the product lines, the Centris models were merged into the Quadra line within a few months.

Quadra AV
In 1993, the Quadra AV series was released, consisting of the Macintosh Quadra 660AV and 840AV, clocked at 25 MHz and 40 MHz respectively. Both included an AT&T 3210 digital signal processor (DSP) and and  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 the DSP was not included in PowerPC-based AV Macs that were introduced later.

Discontinuation
In March 1994, the Power Macintosh replaced the Quadra as Apple's flagship computer line. The Quadra 660AV, 650, and 840AV were superseded by the Power Macintosh 6100, 7100, and 8100.

However, the Macintosh Quadra 630 was released in July 1994 as the last model of the series. It was an upgraded variant of the Macintosh LC 630 and featured a "full" Motorola 68040 processor instead of the LC's 68LC040. The 630 was the first Mac to use to an IDE-based drive bus for the internal hard disk drive, whereas earlier models had used SCSI. A low-end version of the 630 design was also targeted to consumers as the Macintosh Performa 630, leading to further confusion in the marketplace.

Models
All of the Quadra models incorporated Motorola's 68040, which was the last 68k processor that Apple used before switching to PowerPC. All used the "full" 68040 processor, which included the floating-point unit (FPU) except for the entry level Quadra 605 which uses the FPU-less 68LC040.