The first microprocessor in history, Intel 4004 was a 4-bit CPU designed
for usage in calculators, or, as we say now, designed for "embedded applications".
Clocked at 740 KHz, the 4004 executed up to 92,000 single word instructions per second,
could access 4 KB of program memory and 640 bytes of RAM. Although the Intel 4004 was perfect fit for calculators
and similar applications it was not very suitable for microcomputer use
due to its somewhat limited architecture. The 4004 lacked interrupt support,
had only 3-level deep stack, and used complicated method of accessing the RAM.
Some of these shortcomings were fixed in the 4004 successor - Intel 4040.
As the first microprocessor in history, the Intel 4004 is very popular
with CPU collectors and non-collectors. Earlier Intel C4004 CPUs in
white ceramic package are sought-after by beginner and intermediate
collectors, and are usually sold for hundreds of dollars.
The only known second source manufacturer of 4004 microprocessors was
National Semiconductor.
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