How processor lag accidentally created the difficulty curve
In 1978, Tomohiro Nishikado created Space Invaders. The custom hardware he built struggled to render the massive grid of alien sprites, causing the game to run slowly. However, as the player destroyed the aliens, the processor had fewer graphics to render, allowing the remaining aliens to move faster. Rather than fixing this hardware lag, Nishikado kept it, accidentally inventing the concept of an escalating difficulty curve in video games.
Building Hardware from Scratch
In the mid-1970s, video game development was severely constrained by the limitations of commercial microprocessors. When Japanese engineer Tomohiro Nishikado began designing the arcade game that would become Space Invaders for Taito, off-the-shelf microcomputers available in Japan lacked the computational power to handle the complex graphics, movement, and interaction he envisioned. Existing machines were largely dedicated to simple monochromatic paddle-and-ball mechanics or rudimentary driving simulations.
To bring his concept of an animated alien armada to life, Nishikado had to engineer his own custom hardware and software tools. He adopted the Intel 8080 central processing unit, combined it with custom sound circuitry, and implemented a bitmapped video display system. Bitmapped memory allowed the hardware to draw individual pixels rather than relying solely on fixed character generators, granting Nishikado the freedom to render detailed alien animations, descending formations, and dynamic destructible shields.
The Computational Cost of 55 Invaders
Nishikado's design arranged the alien force into five rows of eleven targets, totaling 55 independent sprites moving synchronously across the screen. On modern computing systems, moving dozens of 2D images is trivial, but on an Intel 8080 processor running at approximately two megahertz, every single pixel manipulation consumed precious clock cycles. The processor was responsible for clearing previous sprite positions, calculating collision detection with player projectiles, and redrawing each alien in its new coordinates within video memory.
Because the CPU had to perform these operations sequentially for all 55 aliens, the workload overwhelmed the processor's capacity to maintain a fast, uniform refresh rate. The machine spent so many clock cycles calculating and drawing the full fleet that the overall game loop slowed down significantly. At the start of a round, the alien formation marched across the screen at a sluggish, deliberate crawl, constrained purely by the speed at which the chip could complete its rendering loop.