On April 7, 1982 the first draft of the Atari Sweet 16 Home Computer Product Specifications were written.   Several revisions were made up until June 11, 1982.   The specifications outlined the designs for a new pair of computer systems which would replace the overpriced Atari 400 and 800 systems.   These new systems would come in 2 different memory configurations: 16K and 64K.   They would come in sleek low profile one piece cases with 4 function keys, a built-in HELP key, International character set, an on-board diagnostic system.   The systems would come with a new set of 2 enhanced SIO connectors which would use standard DB-15 connectors, and a new expansion bus connector system called the PBI (Parallel Bus Interface) which would be an 8-bit gateway into each of the custom chips contained within the new systems.

        This new bus would soon be accompanied by an expansion box system called the Atari 1090:  XL Expansion System which would have given the new 1000 series computers 5 expansion slots.  (Although the earlier specifications of the XL Expansion System listed it as having up to 8 slots.)

      These new systems where designated:  The Atari 1000 and the Atari 1000-X.  The 1000 would have 16K memory and the 1000-X would have 64K of memory.    Have you ever wondered why when the Atari 1200XL was introduced, that all its peripherals were not numbered after it, like the Atari 1050 disk drive should have been the Atari 1250, not the 1050.   Or the Atari 1010 cassette recorder should have been the Atari 1210 or the Atari 1025 dot matrix printer should have been the Atari 1225.   These peripherals were designed for the new Atari 1000 line and had the 10xx designations.

      So where does the Atari 1200XL fit in???

      The Atari 1200XL was Atari's final design revision for the Sweet 16 line of computers, actually it was first called just the Atari 1200, there was no XL.   It was decided that since the system had new features it should have (XL: Extended Line).   However the 1200XL was stripped of its major "HIGH END" features outlined in the SWEET 16 designs and was left crippled by management.  (Technie's who have worked on the 1200XL should note all the unnecessary added video circuitry in the 1200XL which didn't improve the video quality over the 800, but actually made it worse).   The idea around the "revised" version of the 1000 Series which became the 1200XL was that Atari Home Computer management felt that the computers should be more like consumer products and less like a hobbyist product, so the idea of expansion bus connections, enhanced Serial I/O (SIO) ports and built-in BASIC were all dropped in favor of a simple, closed box.

           What in turn happened was the original Sweet 16 spec's did eventually surface:  as the Atari 600XL and 800XL computers.   After the 1200XL failed, Atari's computer division management quickly had engineering come up with systems closer to the original Sweet-16 specifications.   However, to keep costs down, the Sweet 16's were placed into cheaper smaller cases with low quality keyboards, the function keys were removed and the only one SIO port was installed.    The true Sweet 16's never made it to market.   The only model Atari computer that comes close to fulfilling the original 1982 dream of the Sweet 16 specifications was the unreleased Atari 1400XL.

The above information was taken from Atari Confidential Trade Secrets file titled Atari Sweet 16 Home Computer Specifications April 7, 1982; April 14, 1982; June 11, 1982.  Ajay Chopra.