The 6502 CPU’s overflow flag explained at the silicon level
The 6502 microprocessor chip
The 6502 is an 8-bit microprocessor that was very popular in the 1970s and 1980s, powering popular home computers such as the Apple II, Commodore PET, and Atari 400/800. The following photograph shows the die of a 6502 processor. Looking at the photograph, it seems impossibly complex, but it turns out that it actually can be understood, using the Visual 6502 group’s reverse engineered 6502. The red box shows that part of the chip that will be explained in this article. The 6502 chip is made up of 4528 transistors (3510 enhancement transistors and 1018 depletion pullup transistors). (By comparison, a modern Xeon processor has over 2.5 billion transistors, which would be almost hopeless to try to understand.)
For more detail: (A small part of) The 6502 chip explained down to the silicon
