The Macintosh Quadra 840AV is a personal computer designed, manufactured and sold by Apple Computer, Inc. from July 1993 to July 1994. It was introduced alongside the Centris 660AV, the "AV" after both model numbers signifying video input and output capabilities, as well as enhanced audio. The 840AV has the same mini tower form factor as the Quadra 800, with a faster Motorola 68040 processor. The Quadra 840AV was discontinued shortly after the introduction of the PowerPC-based Power Macintosh. The Power Macintosh 8100/80AV provided the same functionality in the same form factor, albeit at a significantly higher price point, while the 7100/66AV was priced comparably to the 840AV but in a IIvx-style desktop case.
Hardware
At the time of introduction, its 40 MHz Motorola 68040 CPU and interleaved RAM made it the fastest Macintosh available, topping both the nominally higher-end Quadra 950 and the Quadra 800 by 7 MHz. It remains both the fastest Quadra and the fastest 68k Macintosh of all time, since all later high-end Macintoshes were PowerPC-based Power Macintoshes. The 840AV is also the only Mac to use the 40 MHz-clocked 68040. It also sports a faster 66.7 MHz AT&T DSP 3210 Digital Signal Processor chip, compared with the 55 MHz variant in the 660AV. The on-board DSP was primarily intended to speed up audio/video processing, although few Mac programs made use of this due to the complexity of programming it. The 840AV and its relative, the Centris/Quadra 660AV, marked a number of firsts for the Macintosh family. They were the first Macintoshes to include on-board 16-bit 48 kHz stereo audio playback and recording capability, as well as S-Video and composite video input and output. To improve video playback, two separate frame buffers were used: one for standard graphics, and one specifically for video. This enabled the live video input to be displayed as a scalable "window" within the Macintosh user interface. They were also the first personal computers that supported speech recognition out-of-the-box. The Apple GeoPort Telecom Adapter Kit introduced with the AV Macs added many DSP-based telecommunication functions, such as modem, fax, and telephony. The Quadra 840AV came in a similar case to the earlier Macintosh Quadra 800; the housing, chassis, power supply, and internal storage assemblies are the same, but the front and rear panels changed, with the power button being moved to the back. Internally, the 840AV is significantly different. Apart from the faster processor, the logic board lacks the 800's Processor Direct Slot and second ADB port, but has a DAV slot and the new GeoPort. Also, unlike the 800's 8 MiB of fixed RAM, all of the 840AV's memory is in SIMMs. The way in which the 840AV deals with its memory differs from the other machines of its generation in that 4, 8, 16, or 32 MB 72-pin 60ns SIMMs may be installed up to 128 MB and sizes can be mixed. However, the Quadra 840AV does not support 1 MB, 2 MB, or 64 MB SIMMs. The 840AV and 660AV are the first Macintosh computers to operate in 32-bit mode at all times, and cannot be toggled back to 24-bit mode, which may be useful for using early Nubus cards that conform to the 24-bit addressing.
Trivia
The new AV machines were some of the first to ship standard with an internal CD-ROM drive. The operating system installation package came on CD-ROM rather than a series of floppy disks whenever the CD-ROM drive was included. A hidden QuickTime video included on the original Quadra 840AV/Centris 660AV "Install Me First" CD-ROM, shows the jubilant Cyclone / Tempest design team in the midst of celebrating their accomplishment. In this video, a Cyclone prototype logic board is shown. The logic board is fitted with a 25 MHz 68040, a number of rework wires, and most conspicuously, a daughter card nicknamed "Karma", on which the audio and video input/output ports are located. Notably, the audio and video ports on the card are front-facing, positioned as though they would protrude from an opening in the lower front of the case, where they are more easily accessible to the user. According to a member of the team, the "AV on a card" feature was omitted, because there was not enough room for it in the case. Coinciding with the introduction of both AV Macs, Apple introduced the Apple AudioVision 14 Display, featuring easily accessible audio input, audio output and video input ports of its own, which could be fed by an ADC adapter cable connected with the rear AV ports of the AV Macs. The later Power Macintosh 6100, 7100, and 8100 returned to the "AV on a card" concept, which was later abandoned with the 7500/8500 series machines, and then re-introduced with the "Wings" AV "personality card" of the Power Macintosh G3 "Gossamer" / "Artemis" machines. Stored inside spare ROM space are two JPEG images of the Quadra 840AV development team. Early Quadra 840AV logic boards featured a 2 MB ROM SIMM slot located below the RAM SIMM slots. It was originally planned that the 840AV ROM would contain a bootable image of System 7 within a larger 4 MB ROM space, but Apple dropped this idea before the 840AV shipped. Later revisions of the 840AV logic board included all 2 MB of ROM soldered onto the logic board.
