The COSMAC Elf was an RCA 1802 microprocessor-based computer described in a series of construction articles in Popular Electronics magazine in 1976 and 1977. Through the back pages of electronics magazines, both Netronics and Quest Electronics offered low-priced, enhanced kits that were based on this design. The system was a very early single-board personal computer. It was operated without built-in ROMs and programs were entered directly with help of the CPU integrated DMA using 8 toggle switches and an Input push button.

The COSMAC is an 8-bit microprocessor family introduced by RCA. It is historically notable as the first CMOS microprocessor. The first production model was the two-chip CDP1801R and CDP1801U, which were later combined into the single-chip CDP1802. The 1802 represented the majority of COSMAC production, and today the entire line is known simply as the RCA 1802.