Disabling 'core multi processing'

The other day when playing around in my BIOS I realized what that option meant, and sure enough, when I booted into windows, task manager only showed one processor.

My question is, did it truely disable a whole core, or does it just send the same information to both cores, providing no benefit to me? My goal was to save battery life and heat.

My best guess is that the extra core(s) are off.

By default, all multiprocessor and multicore PCs POST as single CPU, this is called
the BSP or bootstrap processor. It takes operating system code that runs on the BSP
which starts up the other cores or CPUs in the system. (It uses the IOAPIC in the CPU
to send a start command and address to each CPU in the system.)

Until that point, though, the CPUs or cores should be completely powered off except
for their IOAPIC bus interface.

I would have to agree with bz. As you alluded to the whole point would be to save power and the best way would be to completely cut it off.

it turns off a core.

So it probably will save battery life

Ya, one less core to power.