PCI Express, or PCIe, is the high-speed hardware bus used to connect add-in cards such as GPUs, network adapters, and storage controllers to a motherboard. It defines both the physical slot and the communication protocol, so a card has to match the platform’s electrical, mechanical, and firmware expectations, not just fit in the connector.
In cyber security, PCIe matters because it gives attached devices deep access to system resources. A compromised or malicious expansion card can potentially abuse DMA, inject traffic, or interact with memory in ways software defenses may not notice. That is why defenders care about device trust, driver quality, and platform controls such as IOMMU or VT-d, which restrict what peripherals can access. PCIe compatibility also becomes a security issue when hardware is repurposed: an apparently working card may still depend on niche firmware or unsupported drivers, creating reliability and trust risks.