|CPU||Intel 8086 @ 8MHz|
The system was sold in the United States under its original name by Docutel/Olivetti of Dallas. AT&T and Xerox bought rights to rebadge the system as the AT&T 6300 and the Xerox 6060 series, respectively. (AT&T owned 25% of Olivetti around this time.) The AT&T 6300, launched in June 1984, was AT&T's first attempt to compete in the PC compatible market.
Contrary to other PC clones of that era,[dubious ] the M24 was highly compatible with IBM PC. One of its characteristics was the use of the more powerful 8 MHz Intel 8086 CPU rather than the 4.77 MHz Intel 8088 used in IBM's own PC XT  while allowing the installation of the 8087 math co-processor.
The system was designed "split-level", with the motherboard screwed onto the underside of the computer case and connected to the ISA bus backplane in the top section of the case via the video card, which, rather than occupying an ISA slot, has two female edge connectors and plugs onto the ends of both the motherboard and the backplane, doubling as a bridge between them. The M24 has seven 8-bit ISA slots, as were standard for its time, but two of the slots have proprietary second connectors to accept Olivetti 16-bit cards.
The initial release of the AT&T 6300 had either one or two 360k 5.25" floppy drives; a hard disk was not offered. In 1986, AT&T began offering 3.5" 720k floppies and 20MB hard disks. The Xerox 6060 came standard with a single 360k 5.25" drive and a 20MB hard drive.
6300s made in 1986-87 have BIOS Version 1.43 which added proper support for 3.5" floppies and fixed a number of bugs. As with all contemporary systems, a BIOS upgrade required a physical chip replacement, which AT&T provided for $35.
The M24/6300 had an enhanced CGA video card which, in addition to standard 200-line CGA modes, also supported an additional 640x400x2 mode (text mode was 400 lines and had 8x16 character boxes). It required a proprietary dual-sync monitor. The 640x400 graphics mode received a moderate level of support from software developers, mostly in applications (Earl Weaver Baseball is however an example of a game that can use it). Some plasma portables from Compaq and other manufacturers also copied the M24/6300's graphics hardware.
The keyboard used a proprietary 9-pin D-sub connector built into the system board and had the unusual option of plugging a mouse into the keyboard via another 9-pin D-Sub connector. The mouse could be configured to simulate the usage of the keyboard's arrow keys in DOS applications without mouse support.
In Europe, Olivetti also launched a 10-MHz version: the M24 SP, announced in November 1985.
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A January 1985 review in Infoworld declared it "a fair performer, better than the 8088-equipped IBM PC and PC XT and about equal to the 8086-based Compaq Deskpro", and taking pricing into account concluded that it was "a good deal, but by no means perfect." The reviewer wondered how the 5 MHz 8086 in the Compaq ran as fast as the same processor at 8 MHz in the AT&T machine.
The initial model of the AT&T 6300 (no hard disk and only 360K floppy) had slow sales in 1984 with only 28,500 sold compared to 1.5 million IBM PCs. The sales were not much better in the first three months of 1985, with only 8,500 sold in that time period. If fact, worldwide sales of the Olivetti M24 were only 42,000 in the first year, well below the planned production capacity of 200,000. As a result, AT&T introduced the faster models with hard drive and a math co-processor in March. Still, after about one year on the market, AT&T had only claimed about 1% of the PC market, on par with that of TeleVideo and Columbia Data Products, but well below that of Compaq and Kaypro. By December 1986 however, AT&T's PC line (including the 6300 Plus, described below) put it in the fourth place in terms of market share in the US.
Olivetti's M24 did much better in Europe, where it became the market leader in 1986. It produced almost half a million M24 machines that year, about 200,000 of which went to the United States. As it claimed the crown of most PC machines sold in Europe that year, Olivetti also became the third largest PC manufacturer worldwide. Olivetti would however be unable to repeat the feat in the subsequent years, and so 1986 represents the company's apogee in terms of PC market share.
The 6300 was also supported by Unix-based operating systems particularly by Venix/86 Encore, released in September 1984, and by a version of Xenix adapted for the machine by the Santa Cruz Operation, and announced in June 1985.
6300 Plus and subsequent AT&T machines
In October 1985, AT&T launched the 6300 Plus that used a 6 MHz 286 microprocessor in the same case as the 6300. On the hardware level, this machine was criticized by a Infoworld reviewer for being incompatible with AT cards. On the other hand, AT&T sold a package of the 6300 Plus bundled with Simultask, which ran MS-DOS and UNIX System V simultaneously, at a cost—with all software licenses included—on par with the IBM PC AT with MS DOS alone. A review in PC Magazine declared that AT&T's 6300 Plus was "flat out the better machine" compared to the IBM PC AT. (The version of Simultask included with this machine was based on Locus Computing Corporation's Merge software. According to AT&T, their 6300 Plus used non-standard hardware to make such a feat possible given the limitations of the 80286.) The PC6300 Plus shipped with MS-DOS in 1985 though, because its Unix System V distribution was not ready until the end March 1986. The 6300 Plus did not sell as well as the original 6300. Forrester Research estimated in December 1986 that AT&T's financial losses in PC market were about $600M for the year.
After the 6300 Plus, AT&T announced that it was turning over both production and development of its PC products to Olivetti. In 1987, AT&T offered a true AT-based 286, their 6310—a rebadge of Olivetti M28. Equipped with a one-wait state 8 MHz processor, it was a pretty slow machine for its class, even slower than the IBM XT 286. Simultask was also an option for the 6310. The later-released 6312 addressed the speed problem with a 12-MHz CPU. After the announcement of the 6310, in April 1987, AT&T announced price cuts across its 6300 PC product line, with the 6300 Plus discounted by 27-38%, while the original 6300 was discounted by 17-23% (depending on configuration.)
Successors in Olivetti's product line
In response to IBM's launch of their PS/2 line, Olivetti revamped their product line in July 1987 to include 3.5" floppy drives (in 5.25-to-3.5" converted bays though) and also introduced new 386-based products. The M24 (and M24 SP) were succeed by the M240 (8086 at 10 MHz, which AT&T marketed in the USA as the 6300 WGS) while the M28 (and M28 SP) was succeed by the M280 (80286 at 12 MHz). Olivetti also introduced an M380 series (both tower and desktop) using the 80386 processor.
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Locus previously developed Merge 286, now used by AT&T's Simultask program to run one MS-DOS program under Unix on the 80286-based 6300 Plus, according to Judi Uttal, director of marketing for Locus.
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A recent Review Response stated that no special hardware is required to run Simultask [and therefore it could run on any 80286 computer]. Every PC 6300 Plus comes standard with special circuitry on the motherboard. This hardware is activated with Simultask to prevent programs from interfering with one another when they are running simultaneously. This is necessary because many MS-DOS programs have complete control of the hardware. Simultask uses this circuitry to ensure that, no matter what one program does, other programs that are running simultaneously will not be affected. Other computers can't provide this assurance.
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- Bob Troiano's review of the AT&T PC 6300, BYTE, December 1985, page 294-302
- The Man who Plots AT&T's Computer Strategy, InfoWorld, April 15, 1985, p. 16