pGfx, in this context, is referring to the processor-based Intel HD Graphics graphics engine. If no add-in graphics card is present, this engine becomes the primary. If an add-in graphics card is present, this engine is secondary or disabled (the normal BIOS default being to disable it).
PEG stands for PCI Express (PCIe) Graphics and refers to the interface that the processor and chipset together provide for the support of an add-in PCIe graphics card.
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