The PPU (Picture Processing Unit), more specifically known as Ricoh RP2C02 (NTSC version) / RP2C07 (PAL version), is the microprocessor in the Nintendo Entertainment System responsible for generating video signals from graphic data stored in memory.
The chip is known for its effective use of memory, using very little memory to store graphical data. It was rather advanced for its time when the Famicom (Japanese version of the Nintendo Entertainment System) was released, sporting full sprite support, movable backgrounds, and many colors on screen at the same time. To compete with other video game systems, like the graphically superior Sega Master System, Nintendo also extended the PPU's technical capabilities through the use of mappers, which were placed on the game cartridge. The mappers added more memory or could bank switch data into the PPU's address space, making it possible to create more advanced graphics, using more colors and bigger tile sets.