The Bulldozer and Bobcat

AMD has been curiously absent from the value netbook and nettop segments since Atom’s arrival nearly three years ago. These markets are highly profitable only for component vendors, as the OEMs that sell netbooks and nettops must survive on very slim margins in order to hit aggressive price points. It wasn’t too long ago that we were shocked by $699 desktop PCs, but to now be able to get a fully functioning portable PC with display at below $300 is impressive. In order for the profit equation to work out however, you can’t simply scale down a larger chip - you need an architecture targeted specifically at the type of very light workloads you expect to encounter in these segments. Underclocking and undervolting an architecture targeted at high end desktops or servers won’t cut it.

Generally a single microprocessor architecture can cover an order of magnitude of power envelopes. You can take an architecture from 10W - 100W using clock speed, voltage scaling and disabling features (e.g. cutting cache sizes). You can’t efficiently take a 100W architecture and scale it down to 1W. Intel realized this with Atom, and what resulted was a new architecture designed to span the 0.5W - 5W range. Given the constraints of the process (Atom was built at 45nm) and a desire to keep die size down to a minimum (and thus maximize profits), Intel went with a dual-issue in-order architecture reminiscent of the old Pentium - but with a modern twist.

AMD came to the same realization. For it to compete in these value markets, AMD couldn’t rely on its existing Phenom II derived architectures. The Phenom II and its relatives currently span a range of TDPs from 9W to 140W, and at the lower end of that spectrum we’re talking about some very low clock speeds and performance targets. Getting down to 1W was out of the question without a separate design.

What AMD came up with was a core called Bobcat, initially targeted for netbooks, notebooks, nettops and entry level desktops. Architecturally Bobcat is a significant step ahead of Atom: while still dual-issue, it features an out-of-order execution engine making it the Pentium Pro to Atom’s Pentium.

It isn’t just CPU architecture that AMD surpassed Atom with, the first incarnation of Bobcat is an integrated SoC with on-die DirectX 11 GPU. AMD calls this combination a Fusion APU (Accelerated Processing Unit) as it places both a CPU and GPU on a single die. The possible CPU/GPU combinations for Bobcat based APUs are listed in the table below:

AMD Brazos Lineup
APU Model	Number of Bobcat Cores	CPU Clock Speed	GPU	Number of GPU Cores	GPU Clock Speed	TDP
AMD E-350	2	1.6GHz	Radeon HD 6310	80	500MHz	18W
AMD E-240	1	1.5GHz	Radeon HD 6310	80	500MHz	18W
AMD C-50	2	1.0GHz	Radeon HD 6250	80	280MHz	9W
AMD C-30	1	1.2GHz	Radeon HD 6250	80	280MHz	9W

AMD avoided branding its first APUs, they’re simply the AMD E-series and C-series Fusion APUs. The emphasis isn’t on the CPU or the GPU in this case, just the company name and a model number.

AMD's E-350

CPU Specification Comparison
CPU	Manufacturing Process	Cores	Transistor Count	Die Size
AMD Zacate	40nm	2	?	75 mm2
AMD Thuban 6C	45nm	6	904M	346mm2
AMD Deneb 4C	45nm	4	758M	258mm2
Intel Gulftown 6C	32nm	6	1.17B	240mm2
Intel Nehalem/Bloomfield 4C	45nm	4	731M	263mm2
Intel Sandy Bridge 4C	32nm	4	995M	216mm2
Intel Lynnfield 4C	45nm	4	774M	296mm2
Intel Clarkdale 2C	32nm	2	384M	81mm2
Intel Sandy Bridge 2C (GT1)	32nm	2	504M	131mm2
Intel Sandy Bridge 2C (GT2)	32nm	2	624M	149mm2

These APUs do need the aid of an additional chip - the Hudson Fusion Controller Hub (FCH). The FCH adds support for things like SATA, USB, Ethernet and Audio.The Hudson FCH is very tiny measuring approximately 4mm x 7mm for a total die size of around 28mm².

The Hudson FCH

The combination of these Bobcat based APUs and the FCH is called the Brazos platform.

Late last year AMD invited me to spend several hours with a Brazos system at its brand new campus in Austin, TX. While the preview gave us some insight into what we could expect from Brazos, I didn’t have enough time to really dive in as much as I would’ve liked to.

Earlier this month, AMD officially launched Brazos with hardware expected sometime this quarter. For the past couple of weeks I’ve been testing a Brazos mini-ITX motherboard from MSI and today, it’s time to break the silence and share the results. They are quite good.