Some corrections and additions on the technical specifications:
- The CPU is actually a custom designed 65c02-based processor (I believe it is missing a few instructions).
- It has 64K or directly addressable memory, but there is only 4K of actual work RAM. The lower 32K is four copies of the work RAM, some save RAM (located on the cartridge) for saving your progress, and registers for controlling the video and sound subsystems. The upper 32K is reserved for two 16K banks of game ROM.
- There were four / five sound channels available for use (depending on which country you lived in). Some models (U.S. included) had a raw PCM channel, as can be heard in a few games, such as the intro to Skate or Die 2.
The 32K ROM limitation was broken through special hardware located in the game cartridges, called mappers. These hardware devices intepreted special register read/writes by the code, allowing ROM to be swapped in and out of the running system, for games of up to 1024K to be played (only a few were that large, such as Dragon Warrior IV).
The video system (run by a PPU) was quite slick, with four virtual screens (two actual ones, each mirrored) to write to, allowing the screen to be scrolled through each of them with four directions of movement (evident in games such as Crystalis). It took PCs several years to gain the graphical capability of the NES (see Commander Keen).
Even with 4K of RAM though, the NES Chessmaster still humbles me on any but the lowest few levels. Deep Blue, eat your heart out!
Much of the knowledge above I gained from y0shi (Jeremy Chadwick), in his infamous Nintendo Entertainment System documentation from about 10 years ago. He still maintains an excellent hardware reference site at