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Chipsets

AMD A8-3850 Review: Llano Rocks Entry-Level Desktops
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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.

A75 is the chipset most folks will preferA75 is the chipset most folks will prefer

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
FIS-Based Switching
Yes
No
HD Audio
Yes
Yes
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
USB 3.0/2.0/1.1
4/10/2
0/14/2
SD Controller
Yes
Yes
33 MHz Legacy PCI
Up To Three Slots
Up To Three Slots
mSATA Support
Yes
Yes


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.

Source: SATA-IO, Command-based switchingSource: SATA-IO, Command-based switching

Source: SATA-IO, FIS-based switchingSource: SATA-IO, 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.

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