Battle At $140: Can An APU Beat An Intel CPU And Add-In Graphics?

Can AMD's APU Outperform A CPU And Discrete GPU?

When it comes to the mobile space, AMD's APUs based on the Llano architecture are potent. By dedicating more resources to graphics, the company is able to outmaneuver Intel's best effort in workloads that require a more balanced approach than raw processing power.

A quick look at Newegg shows that notebooks equipped with the A4-3400M and A6-3420M start at $500, while models with the A8-3520M can be found as low as $550. If you want a mobile machine based on Intel's CPUs with a fast-enough discrete GPU to compete, you'd need to spend at least $650 (but probably more than $700). The difference is substantial, especially if you have software to buy, too.

Truly, there's no denying the appeal of an APU in a notebook. But we're curious about how AMD's accelerated processing units stand their ground on the desktop, too. The ultimate question to answer is whether an APU at one price (let's call it a $140 A8-3870K) has the chops to outperform a cheap CPU (call that a $70 Pentium G620) and cheap discrete graphics card (we'll use the $70 Radeon HD 6670 with DDR3 memory). If it does, you can add in the convenience of a single-chip solution to AMD's advantages. But if the separate processor and graphics card are faster, you'll need to weigh the pros and cons of each configuration.

We’ll start by comparing processing cores. The A8-3870K boasts four execution cores, while the Pentium G620 comes armed with two (and no Hyper-Threading technology, either). AMD's chip also proffers a faster core clock at 3 GHz, which compares favorably to Intel's 2.6 GHz frequency. Neither processor benefits from a dynamic speed-up capability like Turbo Boost or Turbo Core.

Each core on AMD's APU includes 64 KB of L1 data and L1 instruction cache, totaling 512 KB across the entire processor. It also employs four 1 MB L2 caches (one cache per core), and no L3 cache. The Pentium comes with two 32 KB L1 data and L1 instruction caches, totaling 128 KB, along with two 256 KB L2 caches and a shared 3 MB L3 cache.

On the graphics side, AMD's A8-3870K has 400 shaders clocked at 600 MHz. Intel's Pentium G620 has its own HD Graphics engine that consists of six execution units operating between 650 and 1100 MHz, but we're ignoring that for this story, particularly because its biggest asset, Quick Sync, is disabled in hardware. Instead, we're matching the Pentium processor up to a discrete Radeon HD 6670 DDR3 with 480 shaders operating at 800 MHz. Based on specifications along, the add-in board seems to have a sizable advantage. 

Interestingly, the discrete Radeon card includes 800 MHz DDR memory, and that's what we're using as system RAM, complementing the APU configuration. Also interesting is that, when you add up the power use of Intel's Pentium and AMD's Radeon HD 6670 DDR3, you come up with 101 W. That's one one watt more than the A8-3870K. Crazy, right?

The wildcard is AMD's unlocked multiplier, which facilitates more flexibly overclocking. In comparison, we can't do much with the Pentium's operating frequency. Fortunately, its complementary Radeon HD 6670 can be tweaked. 

Given the specifications, we have to assume that the Pentium and Radeon card, together, will outmaneuver AMD's APU in gaming environments. However, in our processor-oriented productivity tests, four 3 GHz cores should reign supreme over two 2.6 GHz cores, particularly in well-threaded benchmarks.