Video Computer System X

Video Computer System X (or Video System X, or VSX) was the original name of the 5200 prior to its release.  The promotional controller was shown in Atari's marketing literature.

Only 2 known all-black prototypes of the early version of the 5200 known as the Video System X exist.  These are fully functional and all the ICs are socketed.

Only 4 known stainless steel prototypes of the 5200 known as the Video System X exist.

Note the green and red "ATARI" keys, instead of * and #.

The following photo appeared in Consumer Guide's 1982 book How to Win at Video Games: