PCIe Lane

PCIe (Peripheral Component Interconnect Express) lanes are the physical pathways that connect a GPU to the CPU and system memory. Each lane is a bidirectional serial connection. GPUs typically use PCIe x16 slots (16 lanes) for maximum bandwidth. The generation matters: PCIe Gen3 x16 provides approximately 32 GB/s, Gen4 x16 provides approximately 64 GB/s, and Gen5 x16 provides approximately 128 GB/s. In cloud GPU instances, some configurations use fewer lanes (x8 or x4) which can bottleneck data transfer between CPU and GPU. This matters most for workloads with heavy CPU-GPU communication. Modern data center GPUs like A100/H100 support PCIe Gen4/Gen5, but the host system must also support it to achieve full bandwidth.