How would you do this for a 512K bios? Thanks!

Well, since the BIOS is really just a chunk of memory, and dd operates on devices, you will need some way to make memory look like a device. Luckily, we have /dev/mem which does just that. Next you need to know where in the CPU memory map the BIOS is located. My belief is that it is mapped to the top 512K of the 32-bit address space (4GB). This may be architecture-dependent, and since you didn't specify the architecture, I will assume you already know at what address to look.
The above will require root privileges, of course.
--- rod.

thanks , useful for me.