With the 520 and 1040 ST line well established by 1987, it was time for Atari to develop the ST in favour of more lucrative markets.  Most all-in-one computer system designs still had an air of "home computing" about them, and Atari needed to enhance the ST to appear more appealing to the business market, although mostly cosmetic, the Mega ST was the result.

At Comdex on November the 10th 1986, a group of selected Atari partners were shown the new ST1.  This was the first demonstrable unit to be shown and the feedback was very positive.  In conjunction with the new ST1, Atari also previewed its new Laser printer.  Atari was about to launch the most cost effective business computer package available in 1987.

Renamed the "Mega", Atari launched a 2MB and 4MB model.  Not only did the new Mega systems have more RAM than the stock 520/1040 machines, but they had plenty more to shout about.  The Mega was housed in a new square chassis design (nicknamed the "slab" by some) and a fully detached keyboard, it boasted an on board clock, optional Floating Point Co-processor (FPU), Blitter graphics processor and the ability to utilise future internal upgrades or adapters through the internal expansion connector.  The Mega was a beautifully designed upgrade to the ST line.

What really made the Mega line an attractive business option was the new Atari DTP (Desk Top Publishing) package.  This combined either a Mega 2 or 4 system with the new Atari SLM804 Laser printer and Atari's "DeskSet" publishing software (with an optional 20, 30 or 60MB hard drive).  At under $3,000.00, Atari was able to provide an extremely affordable DTP solution which not only rivalled Apple systems, but was cheaper than most Laser printers at the time.

The Mega line also introduced the Atari "Megafile" hard drives which were of the same design as the Mega computer, thus sitting neatly under the main CPU.  Theses came in 20, 30 or 60MB capacities.  Note:  The first hard drive for the mega was actually a 20MB version using the older "SH" designation (ST Hard Drive), the SH-205.  Before it was reborn in the Mega design, the SH-205 was available as a simple but functional external box for the 520 and 1040.

Another Mega designed peripheral was the Megafile 44, a 44MB removable disk product.  In 1989, Atari launched the Mega 1, which was a 1MB version of the Mega computer (less the internal fan).  The Last Mega systems were produced towards the end of 1990, and official stocks had all but been depleted by the middle of 1991 to make way for the Mega STE line.