The Llano-based APU family is accompanied by two AMD-branded chipsets: A75 and A55. One is distinctly current-generation, and the other is awkwardly behind the times.
Both boast Socket FM1 (905-pin) interfaces for the desktop Lynx platform. They similarly include six SATA ports, software RAID 0, 1, and 10 support, HD Audio, four second-gen PCI Express lanes, a PCI bus, and mSATA compatibility.
However, A55 is limited to 3 Gb/s storage connectivity, it doesn’t enable FIS-based switching, and it doesn’t include USB 3.0 support. We have to imagine that A55 will be limited to the all-in-one market, where performance takes a back seat to cost and form factor considerations, though USB 3.0 would still seem to be an important feature there.
|Feature||AMD A75||AMD A55|
|Platform||Socket FM1 (Lynx desktop)||Socket FM1 (Lynx desktop)|
|SATA Connectivity||6 x SATA 6Gb/s||6 x SATA 3Gb/s|
|Software RAID||0, 1, 10||0, 1, 10|
|General-Purpose PCIe||4 x PCI Express 2.0 lanes||4 x PCI Express 2.0 lanes|
|UMI (Connection To APU)||Four-lane PCIe + DisplayPort||Four-lane PCIe + DisplayPort|
|33 MHz Legacy PCI||Up To Three Slots||Up To Three Slots|
A75 is the better-endowed solution. All six of its SATA ports offer 6 Gb/s signaling. And while A55 simply exposes 14 USB 2.0 ports and two 1.1 ports, A75 splits four of those second-gen connectors off as USB 3.0 ports, leaving 10 potential USB 2.0 ports if motherboard vendors choose to implement them. A75 also support FIS-based switching.
That’s an important feature if you’re building a machine with multiple drives in it. FIS-based switching facilitates communication between the storage controller and more than one disk simultaneously, which lets Native Command Queuing work the way it’s supposed to. A controller that doesn’t support FIS-based switching employs command-based switching, which only lets the host issue command to one drive at a time. Obviously, that can impact storage performance.