In the 9500 the CUDA switch, a miniature momentary-action switch with (most often) a red button, is near the daughter-card's slot towards the back of the Mac. In round terms, CUDA (capacitive unit discharge ASIC) is for Old World, and PMU (power management unit) is for New World Macs with the exception of the PCI Graphics G4. CUDA switches are often close to a daughter-card slot, not least because hardware upgrades and changes necessitate, in best practice, that you use the CUDA switch as the last act before you close the Mac and power up, and processor upgrades are chief amongst such hardware changes.
CUDA ad PMU switches are different beasts, and they are used differently, albeit for similar ends. Both are used to clear PRAM, or NVRAM, either because a Mac will not start up or has forgotten what its state is, or to signal to the board that the installed hardware has changed. In worst cases, they both may need to be used after a complete resetting of the MLB. In essence, the CUDA's process continues for as long as the switch is held in, and the PMU's process is begun with a single press-and-release of the identical-looking switch. Twenty to sixty seconds is useful for CUDA activation. Many CUDA switches are in obscure positions, but accessible they are, even if that means that a handlamp and a non-conducting stiff thin rod have to be used to reach them.
Be also aware that the same acronym (CUDA), for Compute Unified Device Architecture, is in use by Nvidia. Confusion is sure to follow, although the two uses (Old World hardware and New World software) will not be likely to occur in the same context.
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