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i am building a very basic computer based on a 6502 design but using a intel 486 DX4 mpu.
i need to know a few things. in the documentation for the processor it says the modes it suports is 8bit 16bit and 32bit when i am using the processor what mode dose it start in.
as as far as i know the 486 in a normal pc will only work in 16bit and 32bit any help pls clering up what i have read and been told.

The way i understand it, 8 bit processors, or 8 bit modes stopped at around the latest the 186. The 286 gave way to 16 bit protected mode support then the 386 gave way to 32bit protected mode support.

All intel base x86 cpus, as far as i always thought, always start in 16bit real mode. Your 486 will start in 16bit real mode. it will support 16/32bit protected mode but it won't do any 8 bit modes. I believe 16 bit real mode will give support to old 8 bit code but your cpu won't have any 8 bit mode.

Software-wise, there are three 16-bit modes (real mode, 16-bit protected mode, virtual 8086 mode) and one 32-bit mode (32-bit protected mode).

Hardware-wise, the 486 has two input pins can be driven to make the chip access memory 16 or 8 bits at a time, instead of 32. These pins are driven by external circuitry (the address decoder), so the bus width varies for each memory access.