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AMD's Radeon HD 7770 GHz Edition


...and the Radeon HD 7750, too.
— 11:01 PM on February 14, 2012

Can you believe it's been over two years since we saw a genuinely new mid-range graphics processor from AMD? Oh, sure, the Radeon HD 6770 and 6750 that came out last April had new video decoding logic and HDMI 1.4a support. But other than that, they were pretty much identical to the Radeon HD 5770 and 5750 from the Fall 2009 catalog, down to the Juniper GPUs under their heatsinks.

It's hard to blame AMD for the lack of progress. When TSMC decided to cancel its 32-nm fab process a few years back, both AMD and Nvidia were left with no choice but to make do at 40 nm until the next process node in TSMC's roadmap became available. What little new silicon AMD and Nvidia produced was reserved for higher price brackets, and other products just stuck around, getting price cuts and minor facelifts along the way.

The Radeon HD 5770 cost $159 when it came out in October of '09. Today, you can nab the same card (and its post-facelift alter ego, the Radeon HD 6770) for as little as $100. That combination of longevity, low price, and solid performance has made this card something of a staple for gamers on a budget. According to the Steam hardware survey, the 5770 is the second-most popular choice for Steam users behind Nvidia's GeForce 9800 series.

In the wake of Valentine's Day 2012, though, the Radeon HD 5770 (and the Juniper chip within) finally reaches the end of its run. At the stroke of midnight tonight, AMD launches the Radeon HD 7700 series, a new mid-range product line featuring 28-nm silicon, AMD's latest and greatest GPU architecture, and purported performance improvements. Can the 7700 series live up to so many months of pent-up desire for new mid-range goodness? That's what we're here to find out.

Cape Verde
Wikipedia says Cape Verde (rhymes with bird) is a republic that spans a small archipelago in the central Atlantic, about 350 miles off the African coast. What does that have to do with graphics processors, you ask? Absolutely nothing. But it so happens that AMD chose Cape Verde as the code-name for its latest GPU, which is featured in the Radeon HD 7700 series. Cape Verde is, fittingly, part of the Southern Islands GPU family that includes Tahiti and the soon-to-follow Pitcairn.

At 123 mm², Cape Verde isn't very big. It's actually even smaller than the Radeon HD 5770's Juniper chip, whose footprint was around 166 mm². Thanks to TSMC's 28-nm process technology, however, Cape Verde manages to pack a whopping 1.5 billion transistors inside its diminutive die—that's a 44% increase over Juniper's 1.04 billion transistors.

There's much more to Cape Verde than a higher transistor count, of course. AMD has endowed this tiny slab of silicon with its Graphics Core Next architecture, giving it all of the same features as AMD's new flagship GPU, the Radeon HD 7970. Those features include PCI Express 3.0 compatibility, DirectX 11.1 support, a hardware video encoder block (VCE), improved power management, and last but certainly not least, a revamped shader architecture that's more efficient and should perform better under general-purpose workloads (think OpenCL and the like).

We could devote entire pages to detailing those features. In fact, we already did, which is why I'm going to spare my fingers and point you to the relevant section of our Tahiti review. Cape Verde and Tahiti share the same architectural DNA, a fact AMD emphasized time and again when it spoke to us last week.

As you might expect, AMD dusted off the world's smallest chainsaw in order to make Cape Verde suitably small and cheap to manufacture. Take a look at the block diagram below, which provides an abstracted, top-down view of Cape Verde's various odds and ends:


Source: AMD

Now compare that with Tahiti's block diagram, which we posted here. Cape Verde has only 10 compute units (down from 32 in Tahiti), two 64-bit memory controllers (down from six), four ROP partitions (down from eight), and one geometry engine (down from two). Since the two chips are based on the same core graphics architecture, however, Cape Verde's compute units each contain the same number of 16-wide vector units (four) and texture units (also four). Cape Verde also has four color and 16 Z/stencil ROP units inside each ROP partition—again, just like Tahiti.

Here's how Cape Verde stacks up once you do the math:

  ROP
pixels/
clock
Texels
filtered/
clock
(int/fp16)
Shader
ALUs
Rasterized
triangles/
clock
Memory
interface
width (bits)
Estimated
transistor
count
(Millions)
Die
size
(mm²)
Fabrication
process node
Juniper 16 14/34 800 1 128 1040 166 40 nm
Cape Verde 16 40/20 640 1 128 1500 123 28 nm
Tahiti 32 128/64 2048 2 384 4310 365 28 nm

Depending on what part of the GPU you look at, Cape Verde has roughly one half to roughly one third the execution resources of Tahiti. It's also outfitted a little differently than Juniper, with more texture filtering resources but fewer ALUs. I should note that Juniper is based on AMD's older and less efficient VLIW5 architecture, however, so the figures above don't tell the whole story.

Anyway, that's Cape Verde for you: a new chip, a new architecture, and the promise of a breath of fresh air for cash-strapped gamers looking to upgrade. AMD isn't just launching a new GPU by itself, of course. Cape Verde is making its entrance astride two graphics boards, the Radeon HD 7770 GHz Edition and the Radeon HD 7750. Before we lose ourselves in the fervor of game benchmarking, we should take a moment to introduce these cards.