using a bitmapped framebuffer, and uses monaural sound hosted by a combination of analog circuitry and a Texas Instruments SN76477 sound chip. The adoption of a microprocessor was inspired by Gun Fight (1975), Midway's microprocessor adaptation of Nishikado's earlier discrete logic game Western Gun, after the designer was impressed by the improved graphics and smoother animation of Midway's version. Space Invaders also adopted the multi-chip barrel shifter circuit first developed by Midway for Gun Fight, which had been a key part of that game's smoother animation. This circuit allowed the 8080 CPU to shift pictures in the graphics framebuffer faster than it could using only its own native instructions. Despite the specially developed hardware, Nishikado was unable to program the game as he wanted—the Control Program board was not powerful enough to display the graphics in color or move the enemies faster—and he ended up considering the development of the game's hardware the most difficult part of the whole process. While programming the game, Nishikado discovered that the processor was able to render each frame of the alien's animation graphics faster when there were fewer aliens on the screen. Since the alien's positions updated after each frame, this caused the aliens to move across the screen at an increasing speed as more and more were destroyed. Rather than design a compensation for the speed increase, he decided that it was a feature, not a bug, and kept it as a challenging gameplay mechanism. Taito released Space Invaders in July 1978. They released both an upright arcade cabinet and a so-called "cocktail-table" cabinet; following its usual practice, Taito named the cocktail version T.T. Space Invaders ("T.T." for "table-top"). Midway released its upright version a few months later and its cocktail version several months after that. The cabinet artwork featured large humanoid monsters not present in the game; Nishikado attributes this to the artist basing the designs on the original title of "Space Monsters", rather than referring to the actual in-game graphics. In the upright cabinets, the game graphics are generated on a hidden CRT monitor and reflected toward the player using a semi-transparent mirror, behind which is mounted a plastic cutout of a moon bolted against a painted starry background. The backdrop is visible through the mirror and thus appears "behind" the graphics. Both Taito's and Midway's first Space Invaders versions had black-and-white graphics with a transparent colored overlay using strips