- The Z-80 has a 4-bit ALU. Here’s how it works. (righto.com)
The 8-bit Z-80 processor is famed for use in many early personal computers such the Osborne 1, TRS-80, and Sinclair ZX Spectrum, and it is still used in embedded systems and TI graphing calculators. I had always assumed that the ALU (arithmetic-logic unit) in the Z-80 was 8 bits wide, like just about every other 8-bit processor. But while reverse-engineering the Z-80, I was shocked to discover the ALU is only 4 bits wide! The founders of Zilog mentioned the 4-bit ALU in a very interesting discussion at the Computer History Museum, so it’s not exactly a secret, but it’s not well-known either.
- Galaga (Wikipedia)
Galaga is a 1981 fixed shooter video game developed and published by Namco for arcades. In North America, it was released by Midway Manufacturing. It is the sequel to Galaxian (1979), Namco’s first major video game hit in arcades. Controlling a starship, the player is tasked with destroying the Galaga forces in each stage while avoiding enemies and projectiles. Some enemies can capture a player’s ship via a tractor beam, which can be rescued to transform the player into a “dual fighter” with additional firepower.