AT89S Microcontroller Series
Atmel AT89S microcontrollers, including AT89S2051 in 20 pin packages. 8051 series code
AT89C2051 Atmel Microcontroller
AT89C2051 Microcontroller - 20-pin DIP
The AT89C2051 is a low-voltage, high-performance CMOS 8-bit microcomputer with 2K bytes of Flash programmable and erasable read only memory...
AT89S are 8051 series microcontrollers from Atmel, now Microchip, updated with reprogrammable flash and ISP