The SX52 Processor was one of a line of 8 bit microcontrollers designed by Ubicom. It was based on the PIC

PIC microcontroller

PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division...

 architecture and housed in a 52 pins package.
When Parallax, inc.

Parallax, Inc. (company)

Parallax Inc. is a privately held company in Rocklin, California. Parallax Inc. designs, manufactures, and sells BASIC Stamp microcontrollers, Propeller microcontrollers, microcontroller accessories Parallax Inc. is a privately held company in Rocklin, California. Parallax Inc. designs,...

 took over the SX line of microcontrollers

Parallax SX

The Parallax SX line of microcontrollers were formerly made by Ubicom, who was originally Scenix, hence the SX- prefix. The SX dies are still manufactured by Ubicom, who sends them to Parallax for packaging...

 they could not support the 18 and 52 pins packages so the SX18 and the SX52 processors became obsolete. Currently SX processors are available in 20, 28 and 48 pins packages.
Ubicom is still the manufacturer of the dies

Die (integrated circuit)

A die in the context of integrated circuits is a small block of semiconducting material, on which a given functional circuit is fabricated.Typically, integrated circuits are produced in large batches on a single wafer of electronic-grade silicon or other semiconductor through processes such as...

, but sends them to Parallax for packaging.