already limited addressable memory to 4 KB (212 = 4096). This was believed to be sufficient as Combat is itself only 2 KB. Later games circumvented this limitation with bank switching. The console has 128 bytes of RAM for scratch space, the call stack, and the state of the game environment. The top bezel of the console originally had six switches: power, TV type selection (color or black-and-white), game selection, player difficulty, and game reset. The difficulty switches were moved to the back of the bezel in later versions of the console. The back bezel also included the controller ports, TV output, and power input. Graphics The Atari 2600 was designed to be compatible with the cathode-ray tube television sets produced in the late 1970s and early 1980s, which commonly lack auxiliary video inputs to receive audio and video from another device. Therefore, to connect to a TV, the console generates a radio frequency signal compatible with the regional television standards (NTSC, PAL, or SECAM), using a special switch box to act as the television's antenna. Atari developed the Television Interface Adaptor (TIA) chip in the VCS to handle the graphics and conversion to a television signal. It provides a single-color, 20-bit background register that covers the left half of the screen (each bit represents 4 adjacent pixels) and is either repeated or reflected on the right side. There are 5 single-color sprites: two 8-pixel wide players; two 1 bit missiles, which share the same colors as the players; and a 1-pixel ball, which shares the background color. The 1-bit sprites all can be controlled to stretch to 1, 2, 4, or 8 pixels. The system was designed without a frame buffer to avoid the cost of the associated RAM. The background and sprites apply to a single scan line, and as the display is output to the television, the program can change colors, sprite positions, and background settings. The careful timing required to sync the code to the screen on the part of the programmer was labeled "racing the beam"; the actual game logic runs when the television beam is outside of the visible area of the screen. Early games for the system use the same visuals for pairs of scan lines, giving a lower vertical resolution, to allow more time for the next row of graphics to be prepared. Later games, such as Pitfall!, change the visuals for