PCIe Add-in Card (AIC)
Direct Answer
PCIe Add-in Card (AIC) SSDs, commonly called HHHL (Half-Height, Half-Length), plug directly into a PCIe expansion slot like a graphics card rather than using M.2 or U.2 connectors -- trading compactness for the far greater power delivery and cooling surface area a full expansion card provides.
Source: PCI-SIG expansion card form factor
Specs
| Form Factor | Half-Height, Half-Length (HHHL) PCIe expansion card |
| Slot Power Available | Up to 75W (PCIe x16 slot) |
| Typical Use | High-performance enterprise/datacenter and enthusiast drives |
Trading Compactness for Headroom
A PCIe Add-in Card SSD, commonly abbreviated AIC or called HHHL for its half-height, half-length card dimensions, plugs directly into a PCIe expansion slot rather than a dedicated M.2 or U.2 connector -- the same basic slot a graphics card uses, though typically at a narrower PCIe x4 or x8 link width for the drive itself. This form factor predates M.2 and U.2 standardization, having been one of the original ways to deliver PCIe-bus speeds to storage in servers.
A PCIe x16 slot can supply up to 75W of power, far beyond what M.2's edge connector provides, and the card's much larger PCB area leaves room for a substantial heatsink -- giving AIC SSDs better sustained cooling and power headroom than M.2 under heavy, continuous load. The tradeoff is size and slot availability: an AIC SSD occupies a full expansion slot the way a graphics card does, rather than tucking onto the motherboard. It remains in use for high-performance, high-capacity drives in servers and enthusiast desktops where an M.2 or U.2 drive would thermal-throttle.