BTW. Quick and approximate cheat sheet, especially for people who might be reading this thread that are less familiar with the history:
8051: Usually the label for the Architecture. Aka "MCS-51"
Also, an Intel chip with 4k internal ROM and 128 bytes RAM.
8052: Chip with 8k internal ROM and 256 bytes RAM.
8031, 8032: like 51/52, only no internal ROM. Could only be used in "external program memory" configurations. pre-programmed 8052/etc would appear on the surplus markets as "8032", since the same wiring for external program memory would simply bypass any internal program memory that happened to exist.
80C52/etc: Like 8051, only CMOS instead of NMOS - lower power!
87C52/etc: Like 8052/etc, only with internal EPROM (UV-erasable) rather than ROM. Usually ceramic package with quartz window for UV-erasure. (Later, plastic with no window for One-time programming (OTP))
89C52: like 87C52, but with FLASH internal program memory. (Atmel part number)
89C2051: low pin count (20pin) variant with 2k Flash and 128bytes RAM (Atmel.)
89S52: like 89C52, but with In-circuit Serial Programming. Devices earlier than this required complex HV parallel programming. (Atmel part number)
Sometime around then everyone started shipping 8051 clones (when Intel lost interest? When they opened up the IP? I dunno.) Different vendors used different part number schemes to indicate different features/memorysize/memory technology. On some, the numbers tell the story. Others, alphabetic suffixes are more relevant...
The original architecture uses as least 12 clock cycles for each instruction. Intel implemented a faster version (MCS-151) that did 2 clocks, and I think since then many vendors have done single-clock versions without being explicit via part numbering. (This is "clock cycles per machine cycle", some instructions require more than one machine cycle.) (This has some substantial impact on external program memory and such...) (There's some microcontroller history in here somewhere. 8bit PICs are widely sneered at these days for using 4 clocks/machine cycle. But when they were first introduced, that was pretty uncommon...)
There was a follow-on MCS-251 architecture introduced by Intel, but it didn't go very far. (IIRC, Intel exited the microcontroller business shortly after introducing the architecture, and may have been fussier about licensing. And by then, there were a lot more competing microcontroller architectures.)