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AMD Radeon HD 7770 And 7750 Review: Familiar Speed, Less Power

AMD Radeon HD 7770 And 7750 Review: Familiar Speed, Less Power
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These are the lowest-end cards built using AMD's new Graphics Core Next architecture. Is 28 nm manufacturing, a fresh design, and new functionality enough to warrant upgrading existing value-oriented champs like the Radeon HD 6850 and GeForce GTX 460?

If you’re a regular Tom’s Hardware reader, then you’re already familiar with our monthly Best Graphics Cards for the Money column, written by Don Woligroski. Basically, Don maintains a list of the most value-oriented purchases at a number of given price points to help game enthusiasts make purchasing decisions. Once upon a time, the list was absolutely dominated by hardware from Nvidia. Slowly, though, I’ve watched it shift the other direction. And each month, as I’m editing the column, I grill Don on his selections in order to make sure the right recommendations make it in.

Well, for February, there were 18 total cards in his list, split between full endorsements and less enthusiastic honourable mentions. Fourteen of those were AMD cards. Four came from Nvidia. Under £180, every single card was a Radeon. Every. Single. One.

Right now, AMD is simply rocking the budget gaming space with cards like the Radeon HD 6770 and 6850. But with a new generation of derivatives following behind the Radeon HD 7970 and 7950, it’s hoping to trump existing recommendations with the Graphics Core Next architecture, along with a handful of value-adds.

To be sure, its fiercest competition doesn’t come from Nvidia. Rather, the company must do battle with its own compelling portfolio of fast, affordable gaming cards.

High-End? Check. Low-End? Check

After covering enthusiasts with those aforementioned 7900-series cards based on its Tahiti GPU, AMD is addressing the entry-level space with Radeon HD 7770 and 7750. Both boards sport the same Cape Verde graphics processor, manufactured using TSMC’s 28 nm node, in slightly different configurations.

Compared to Tahiti, a 4.31 billion-transistor, 365 square millimetre die, Cape Verde sports 1.5 billion transistors in a 123 square millimetre package. Its most complete configuration consists of 10 Compute Units, each one composed of four Vector Units containing 16 Stream Processors. All told, that’s as many as 640 shaders based on the Graphics Core Next architecture.

Cape Verde is equipped with four ROP partitions—half as many as Tahiti—limiting it to 16 raster operations per clock cycle. A memory crossbar connects those partitions to a pair of 64-bit dual-channel memory controllers, yielding a 128-bit aggregate bus.

Clearly, AMD took an interesting path to get from the Radeon HD 7970’s Tahiti to the 7770’s Cape Verde. Armed with 31% of the flagship GPU’s shaders and texture units, 50% of its ROP partitions, 66% of its L2 cache, and a mere 27% of its peak memory bandwidth, company representatives say they ran simulations and these were the ratios that turned back optimal performance. The target, they claim, is playable 1920x1080 performance. So, while frame rates may fall off at higher resolutions with AA turned up, that’s perfectly acceptable for a fairly mid-range card. Just don’t expect to do much multi-monitor gaming.

The gaping hole between AMD’s highest- and lowest-end Radeon HD 7000s won’t persist for long. Right in the middle, where the Radeon HD 6870 and 6900s currently live, you’ll soon see a third distinct GPU called Pitcairn. Back on topic, though…

Radeon HD 7770 And 7750

Officially, the top-end Cape Verde part is called Radeon HD 7770 GHz Edition, paying homage to its 1 GHz core clock. This is a milestone, AMD says, meaning every partner board will bear the moniker, regardless of whether it’s a stock reference board or a faster configuration with aftermarket cooling. Of course, we all know that the core’s operating frequency is only one variable in the complex equation that defines a board’s performance, so that name ends up rubbing as self-congratulatory and, ultimately, superfluous.

The Radeon HD 7770’s 1 GHz Cape Verde GPU employs all 640 available shaders, theoretically yielding 1.28 TFLOPS of compute performance. Since each Compute Unit includes four texture units, 7770 also sports 40 texture units. An unmolested back-end turns up four ROP partitions and a 128-bit memory bus populated by 1 GB of GDDR5 memory at 1125 MHz.

Measuring 8.5” long, this dual-slot card’s dimensions are almost identical to the Radeon HD 5770 we test it against. Whereas that older Juniper-based board uses a centrifugal fan to exhaust heat, the 7770 employs an axial fan mounted on an aluminium extruded heat sink. We’re normally not advocates of designs that recirculate hot air. However, an 80 W typical board power rating is conservative enough that other subsystems in a closed chassis shouldn’t be affected.

That 80 W rating exceeds the PCI Express bus’ 75 W limit, so the Radeon HD 7770 does require one six-pin auxiliary power connector. Even still, the 5770 was rated at 108 W—almost 30 W higher. Even more impressive, AMD’s Radeon HD 7770 benefits from the company’s suite of ZeroCore technologies, which purportedly take power use under 3 W during long idle periods.

Although one full slot on the 7770’s I/O panel is devoted to ventilation, you’ll still find one dual-link DVI port, one full-sized HDMI connector, and two mini-DisplayPort outputs back there, cumulatively supporting up to six screens (though practically, the limit is still four, since we still haven’t seen any DisplayPort 1.2 Multi-Stream Transport hubs).


Radeon HD 7770
Radeon HD 7750
Radeon HD 6850
Radeon HD 5770
Stream processors
640
512
960
800
Texture Units
40
32
4840
ROPs
16
16
3216
Graphics Clock
1000 MHz
800 MHz775 MHz850 MHz
Texture Fillrate
40 Gtex/s
25.6 Gtex/s
37.2 Gtex/s49.4 Gtex/s
Memory Clock
1125 MHz
1125 MHz1000 MHz1200 MHz
Memory Bus
128-bit
128-bit256-bit128-bit
Memory Bandwidth72 GB/s
72 GB/s
128 GB/s76.8 GB/s
Graphics RAM
1 GB GDDR5
1 GB GDDR5
1 GB GDDR51 GB GDDR5
Die Size
123 mm2
123 mm2
255 mm2166 mm2
Transistors (Billion)
1.5
1.5
1.71.04
Process Technology
28 nm
28 nm40 nm
40 nm
Power Connectors
1 x 6-pin
None1 x 6-pin
1 x 6-pin
Maximum Power
80 W
55 W
127 W
108 W
PCI Express
3.0
3.0
2.0
2.0
Price
£125
£90
~£120
~£95


The Radeon HD 7750 is a drastically different graphics card, even though the same piece of silicon serves as its foundation. A 55 W power rating means that it doesn’t need an auxiliary connector at all—just a 16-lane PCI Express slot. And a 6.5” PCB is short enough to fit in space-constrained environments like diminutive desktops and HTPCs. We haven’t seen a serious graphics card with single-slot cooling for a while, but this board manages challenging feat, too.

Of course, there are necessary compromises. Two of Cape Verde’s CUs are disabled, leaving 512 functional shaders and 32 texture units. Also, core clock rate drops to 800 MHz, reducing peak compute performance to 819 GFLOPS.  AMD does leave the back-end alone. One gigabyte of GDDR5 running at 1125 MHz on a 128-bit bus feeds four ROP partitions.

AMD says the 7750 also supports six screens, though with one dual-link DVI port, one full-sized HDMI connector, and one mini-DisplayPort connector, your options for getting there are more limited.

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  • 2 Hide
    bobbyp86 , 15 February 2012 17:33
    The 7770 is not good value at all, I bought my 6770 for £80 last year. Aria.co.uk are selling the 6850 for cheaper than the 7770 and the 6870 for just a tiny bit more. As noted the 7750 has more of a point in a HTPC or SFF build.

    I'm hoping Nvidia have some competition on the way sooner rather than later. At the moment my £250 budget doesn't look like it's going to buy any more performance than it would have done over a year ago :( 
  • 2 Hide
    FinneousPJ , 15 February 2012 20:16
    The architecture looks impressive but the prices seem a bit inflated.
  • 2 Hide
    synthaside , 15 February 2012 23:11
    Origionally i was thinking of upgrading from my long serving 5770' which used to be a pair until one bought the farm and was RMA'ed for a refund ( they were unable to source a replacment xfx 5770 )

    With a pair of these ... it doesnt seem like i would be getting much more oomph for the investment .. they would be a lot better as a £100 card considering how they perform , power draw means next to nothing in a mid level enthuisiast arena price / performance ratio really is king.

    Perhaps is time to look elsewhere ..
  • 0 Hide
    aje21 , 16 February 2012 01:35
    Quote:
    AMD is addressing the entry-level space with Radeon HD 7770 and 7750

    Really, so nothing to replace the lower end boards then? (Or is there something below entry-level now?)
    Would expect to see something like a 76xx or below as the real entry level.
  • 0 Hide
    wifiwolf , 16 February 2012 02:17
    You can't really compare gtx 460 performance with dx 11 graphics using dx11 path
  • 0 Hide
    wifiwolf , 16 February 2012 02:19
    aje21Really, so nothing to replace the lower end boards then? (Or is there something below entry-level now?)Would expect to see something like a 76xx or below as the real entry level.


    In earlier news it's stated that 76xx and below will be rebrands and trinity
  • 0 Hide
    seumas_beathan , 16 February 2012 06:20
    These cards are really bad for the price, the 7750 bearly beats the 5770
  • 0 Hide
    9_breaker , 17 February 2012 15:29
    the 7770 will have better value when it drops it also has low power consumption so you wont need a expensive psu.
  • 0 Hide
    bosing , 26 February 2012 17:59
    So, hold on. Am I not safer with this and a highly rated 400W PSU, than the 6850? There's savings here: at least I can cop out of a new PSU.
  • 0 Hide
    Gusta_Cz , 28 January 2014 16:39
    Mine HD 7770 can get ULTRA settings on BF3 w/ AA x4 on 1920x1080