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The 8051′s predecessor, the 8048, was used in the keyboard of the first IBM PC, where it converted keypresses into the serial data stream which is sent to the main unit of the computer. The 8048 and derivatives are still used today[update] for basic model keyboards.
The 8031 was a cut down version of the original Intel 8051 that did not contain any internal program memory (ROM). To use this chip external ROM had to be added containing the program that the 8031 would fetch and execute.
The 8052 was an enhanced version of the original 8051 that featured 256 bytes of internal RAM instead of 128 bytes, 8 kB of ROM instead of 4 kB, and a third 16-bit timer. The 8032 had these same features except for the internal ROM program memory. The 8052 and 8032 are largely considered to be obsolete because these features and more are included in nearly all modern 8051 based microcontrollers.
Payne, William (December 19, 1990) (in English) (hardcover). Embedded Controller Forth for the 8051 Family. Elsevier. pp. 528. ISBN 978-0125475709.