The 6502 microprocessor is the starting architecture we will be examining over the next couple of weeks, before jumping to something more recent.
The 6502 is an 8-bit microprocessor that was designed by a team from MOS Technology, and led by Chuck Peddle. It is a little-endian 8-bit processor with a 16-bit address bus. The 6502 uses a Programmable Logic Array (PLA) instead of a microcode ROM, and the PLA takes about 15% of the chip area.
When the 6502 came to market, it was the cheapest microprocessor that your average consumer could afford. It came to market at just $25. Which was a more realistic price point for your average consumer to purchase and tinker with.
The 6502 could be found in devices such as (now) vintage gaming consoles: Nintendo Entertainment System, the Atari 2600 and also in early personal computers: Commodore 64, Apple II, and the Atari 8-bit family.
The original 6502 used about 151 of the 256 possible opcodes, organized into 56 instructions with multiple addressing modes.
Here is a resource to the instructions.