The ZX Spectrum is a landmark in home computing, not because of its off-the-shelf components, but because of one chip: the Uncommitted Logic Array (ULA). Designed by Richard Altwasser and fabricated by Ferranti, this 40-pin chip replaced dozens of TTL logic chips, slashing costs and enabling Sinclair to deliver a color computer for under £125 in 1982.
It managed keyboard scanning, the speaker "beeper," and the cassette tape interface. Designing Your Own Retro Computer Inside the ZX Spectrum ULA & How to
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The Silicon Alchemist: The ZX Spectrum ULA and the Art of Efficient Design not because of its off-the-shelf components