History of CPU
| November 1971 was when the first single chip CPU was invented. It was also referred to as the Intel 4004. It was a 4-bit processor that was made for a calculator, and it had its own data and program. Then in 1972, the 4-bit TMS 1000 was launched by Texas Instruments. |
It was considered to be the first microprocessor, which included sufficient RAM, with room for a program ROM, which could facilitate operation without a number of external support chips. It also came with a ground-breaking feature that could add routine instructions to the CPU.
The 8008 was succeeded by the 8080 in April 1972. The 8008 came with 14-bit PC and addressing, but the improved 8080 had a 16 bit address bus, along with an 8 bit data bus. Internally it came with seven 8-bit registers, a 16-bit stack pointer to memory that replaced the 8-level internal stack of the 8008, as well as a 16-bit program counter. In addition, it had a few 256 I/O ports, which allowed I/O devices to be connected without disturbing the addressing space, and a signal pin that let the stack take up a separate memory bank. In 1976, the design was upgraded by Intel with the 8085. Two instructions were added to enable or disable 3 added interrupt pins and the serial I/O pins, and the hardware was simplified with the use of only +5V power, with an added clock generator and bus controller circuits on-chip.
When the Z-80 came to the market, it was expected to be a far better version of the 8080, and it was. What made it really popular was its memory interface, since the CPU produced its own RAM refresh signals, leading to reduced system cost and simpler design.
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