History
The initial ASICs used gate array technology. Ferranti produced perhaps the first gate-array, the ULA (Uncommitted Logic Array), around 1980. An early successful commercial application was the ULA circuitry found in the 8-bit ZX81 and ZX Spectrum low-end personal computers, introduced in 1981 and 1982. These were used by Sinclair Research (UK) essentially as a low-cost I/O solution aimed at handling the computer's graphics. Some versions of ZX81/Timex Sinclair 1000 used just four chips (ULA, 2Kx8 RAM, 8Kx8 ROM, Z80A CPU) to implement an entire mass-market personal computer with built-in BASIC interpreter.
Customization occurred by varying the metal interconnect mask. ULAs had complexities of up to a few thousand gates. Later versions became more generalized, with different base dies customised by both metal and polysilicon layers. Some base dies include RAM elements.
Read more about this topic: Application-specific Integrated Circuit
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