These pins provide a return path for current and a ground reference voltage. Hundreds of VSS pins are distributed across the socket to reduce impedance and minimize "ground bounce" in high-speed circuits.
| Group | Function | Approx. Count | |-------|----------|----------------| | | CPU core voltage (VCore) | ~200–250 | | VSS | Ground | ~400–500 | | VDD_SOC | SoC / Uncore voltage | ~30–50 | | VDD_MISC | Miscellaneous logic | ~10–15 | | VDDP | DDR PHY voltage | ~10 | | VDD18 | 1.8V standby | ~5 | | DDR4 channels | Memory data/address/control | ~200 | | PCIe lanes | PCIe 3.0/4.0 (depends on CPU) | ~160 | | FCH (chipset) | Promontory chipset link | ~30 | | SATA / USB / GPIO | I/O | ~20 | | Clocks & reset | CLK, PWR_OK, RESET# | ~10 | | SVI2 | Serial Voltage Identification (power management) | 2 | | JTAG / debug | Test/debug | ~10 | am4 pinout
A tiny excerpt of the 32×32 grid (looking at CPU bottom, pins up): These pins provide a return path for current