Which PCIe slot should my GPU be in?

Can somebody explain what a 2 slot and 3 slot GPUs means? 2 slot vs 3 slot gpu USB-C to MagSafe 3 Cable Limited Warranty and Service Your MacBook Pro SDXC card slot HDMI port mm headphone jack MagSafe 3 port Three 2 slot shelving So, you can insert a PCIe GPU into a PCIe slot, but you'll be bottlenecked by the bandwidth limitations of Gen 3 In other words

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