Ever thought of writing an emulator? On Reddit theres /r/EmuDev which is a nice place.
For example you could start by writing a CHIP8 emu, then a Space Invaders Emu. After Space Invaders most people write a Game Boy(almost same CPU as Space Invaders and hardware is well documented) emu, but you could try to do a 8086 PC if you want to know more about "real" computers.
There are free BIOS you can use, and FreeDOS, and then rest of the machine is pretty well documented.
For example you could start by writing a CHIP8 emu, then a Space Invaders Emu. After Space Invaders most people write a Game Boy(almost same CPU as Space Invaders and hardware is well documented) emu, but you could try to do a 8086 PC if you want to know more about "real" computers.
There are free BIOS you can use, and FreeDOS, and then rest of the machine is pretty well documented.