Unified Media Interface
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The Unified Media Interface (UMI) is a point-to-point interconnect used in AMD Accelerated Processing Unit (APU) platforms to link the APU die to the Fusion Controller Hub (FCH).[1][2] The FCH performs the role of the southbridge in earlier chipsets, handling I/O functions including SATA, USB, audio, and legacy interfaces. UMI is based on PCI Express and serves a similar architectural function to Intel's Direct Media Interface (DMI).[3]
Background
Conventional AMD desktop platforms before 2011 used HyperTransport to connect the CPU to the southbridge. When AMD introduced its Fusion APU architecture, which integrates CPU and GPU cores onto a single die, the platform was redesigned around two chips: the APU itself and a companion FCH. UMI was specified as the high-speed link between these two components, replacing HyperTransport for this role in APU-based platforms.
The FCH (codenamed Hudson for the Brazos platform and Bolton for Llano) handles all traditional southbridge functions including SATA storage, USB ports, audio codec, PCI bus, and power management interfaces. All traffic between the APU and these I/O subsystems flows across the UMI link.
Technical specification
UMI is electrically and logically based on PCI Express 2.0, configured as a ×4 link. PCIe 2.0 ×4 provides a raw bandwidth of approximately 2 GB/s in each direction (16 Gbit/s total bidirectional), sufficient for the aggregated I/O traffic of the southbridge-equivalent functions handled by the FCH.
Using a PCIe-derived physical layer allowed AMD to leverage existing PCIe IP and simplified the interface between the APU and FCH compared to a custom bus. The choice also aligned with Intel's approach in DMI, which similarly evolved from a PCIe physical layer.
Adoption
UMI debuted with the Brazos platform in January 2011, connecting the Zacate (E-350) and Ontario (C-50) APUs to the Hudson FCH. It was also used in the Llano platform (2011), which paired A-series APUs with the Hudson-D3 FCH. These platforms targeted mainstream notebooks and budget desktops.
As AMD's APU architecture matured, later generations progressively integrated more FCH functionality into the APU die itself, reducing reliance on an external FCH and eventually making a dedicated UMI link unnecessary in some configurations.
Comparison to Intel DMI
Both UMI and Intel's Direct Media Interface serve the same architectural purpose: a PCIe-based link between the main processor package and the platform controller hub. DMI was introduced earlier (with Intel's Alder Lake/Ich7 chipsets in 2004) and used in mainstream Intel desktop and mobile platforms. Both use comparable bandwidths at similar generations; the key difference lies in their respective platform architectures and chipset pairing requirements rather than fundamental electrical differences.