how does hex reading work?

[CKY-2K/Clay Man]

When you execute a file, how does it start up?
Does it start at the top of the file, and the values tell it which address to go next?

I need to get everything straight.

[kyuusaku]

Are you talking about PC executables?

[tepples]

On NES, at power on, the mapper computes which banks are fixed and which are switchable, and the initial values of the switchable banks. Then the CPU reads a 16-bit little-endian value from the locations mapped to $FFFC and $FFFD in CPU space and sets the program counter to this value.

[WedNESday]

.nes ROM's don't equal executables. He isn't being very specific.

[tokumaru]

I didn't even understand the question, as it really isn't clear what you're talking about.

If you are talking about NES binaries, execution starts at the location pointed by the values at $FFFC and $FFFD, as tepples said. Programs are just a sequence of commands, and the CPU auto-increments the Program Counter (the internal register that point to the next instruction to execute) as it reads and executes each command.

Is that what you're talking about?

[CKY-2K/Clay Man]

Ah, thanks, that clears up alot.
I was mostly talking about NES but thanks for the other info.
Because I didn't know exactly how it knows which addresses to grab values from to put into the registers.