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Tahiti LE, Tested: PowerColor's HD7870 PCS+ Myst Edition

Tahiti LE, Tested: PowerColor's HD7870 PCS+ Myst Edition
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Today, we look at a card between two worlds. Despite a model number that suggests Pitcairn lineage, this board is based on AMD's Tahiti GPU. Does it behave more like its namesake, or the powerful engine actually under its hood? Read on for more!

One man's trash is another man's treasure, right? This proverb isn’t new, so it shouldn’t come as any surprise that not all of AMD's Tahiti GPUs are fully-functional and can be turned into Radeon HD 7970s. In fact, some don't even have the working bits to become stripped-down Radeon HD 7950s. But that doesn't make those chips worthless.

The blocks of functional logic on those handicapped graphics processors should work just as well as those in AMD's better-manufactured GPUs. And that's why we're starting to see companies like TUL Corporation using Tahiti LE parts to create special versions of the Radeon HD 7870. Three companies are selling the TUL-based boards: PowerColor (owned by TUL), VTX3D (also owned by TUL), and Club 3D. Today, we’re going hands-on with the PowerColor card.

The question that begs to be answered is: What exactly is the difference between one of these special Radeon HD 7870s and a true Radeon HD 7950? To begin, let's look at a block diagram of the Tahiti LE graphics processor.

One-quarter of the Graphics Core Next (GCN) clusters are disabled, taking the chip's 2,048 ALUs and cutting that number down to 1,536 active shader units. Each GCN compute unit has four texture units tied to it. So, when eight of the GPU's 32 CUs get switched off, so too do 32 of its texture units. A Tahiti LE consequentially exposes 96, rather than 128 texture units.

The GPU's back-end is independent of the shader cores, so AMD chooses to leave all eight ROP clusters turned on, fielding up to 32 full-color raster operations per clock cycle. It cuts back, however, on Tahiti LE's peak memory bandwidth by bypassing two of six 64-bit controllers. Instead of the 384-bit aggregate interface you get from a Radeon HD 7950 or 7970, these boards make due with 256-bit connections. Narrowing the memory bus has a second effect: cutting capacity from 3 GB to 2 GB of on-board GDDR5. To help compensate, PowerColor increases the memory clock rate from 1,250 MHz to 1,500 MHz, pushing peak bandwidth all the way to a respectable 192 GB/s.

A 925 MHz base core frequency isn't bad either, compared to a Radeon HD 7950's 800 MHz. AMD's Boost feature keeps the new chip running at 975 MHz more often than not, though.

Naturally, a comparison between this card and the original Radeon HD 7950 is going to be interesting. Have a look at their respective specifications, along with some of the other boards competing for space in your mid-range to high-end gaming PC.

PowerColor HD7870 PCS+ Myst Edition (Tahiti LE)
 Radeon
HD 7850
Radeon
HD 7870
PowerColor
HD7870
Myst Edition
Radeon
HD 7950
Radeon
HD 7950
Boost Edition
GeForce
GTX 660Ti
GeForce
GTX 670
Shader Units1,0241,2801,5361,7921,7921,3441,344
ROPs3232323232
2432
GPU
PitcairnPitcairnTahitiTahitiTahiti
GK104GK104
Memory Size2 GB
2 GB
2 GB3 GB3 GB
2 GB
2 GB
Memory Bus Bandwidth256-bit256-bit256-bit384-bit384-bit
192-bit256-bit
GPU Clock860 MHz1,000 MHz925 MHz/
975 MHz
800 MHz850 MHz/
925 MHz
915 MHz
+ Boost
915 MHz
+ Boost
Memory Clock1,200 MHz1,200 MHz1,500 MHz1,250 MHz1,250 MHz
1,502 MHz1,502 MHz
Display 60 Comments.
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Top Comments
  • 26 Hide
    EzioAs , February 11, 2013 3:28 AM
    Quote:
    If it cant CFX with a 78xx, it has no right to be called a 7870+ . Marketing name fail +1.


    I agree. AMD has already establish good model naming scheme (X900 for high-end gaming, X800 for mid-range, X700 for low end gaming) after the 6000 series. To be honest, I say it's stupid not to call this chip the HD7930.
  • 23 Hide
    mayankleoboy1 , February 11, 2013 3:22 AM
    Isnt this review quite a bit late ? IIRC, the card came ~1.5 months back...

    If it cant CFX with a 78xx, it has no right to be called a 7870+ . Marketing name fail +1.
    The chip by itself is fine, though.
  • 16 Hide
    EzioAs , February 11, 2013 3:25 AM
    That's quite a short review. It's not anything I haven't looked at other sites. Anyway, at the current price, I really have to agree the 7870XT (Tahiti LE) are excellent cards.
Other Comments
  • 23 Hide
    mayankleoboy1 , February 11, 2013 3:22 AM
    Isnt this review quite a bit late ? IIRC, the card came ~1.5 months back...

    If it cant CFX with a 78xx, it has no right to be called a 7870+ . Marketing name fail +1.
    The chip by itself is fine, though.
  • 16 Hide
    EzioAs , February 11, 2013 3:25 AM
    That's quite a short review. It's not anything I haven't looked at other sites. Anyway, at the current price, I really have to agree the 7870XT (Tahiti LE) are excellent cards.
  • 26 Hide
    EzioAs , February 11, 2013 3:28 AM
    Quote:
    If it cant CFX with a 78xx, it has no right to be called a 7870+ . Marketing name fail +1.


    I agree. AMD has already establish good model naming scheme (X900 for high-end gaming, X800 for mid-range, X700 for low end gaming) after the 6000 series. To be honest, I say it's stupid not to call this chip the HD7930.
  • 13 Hide
    Azn Cracker , February 11, 2013 3:48 AM
    Or maybe the 7950 LE since its pretty much the same card just slower.
  • 7 Hide
    hero1 , February 11, 2013 4:06 AM
    Azn CrackerOr maybe the 7950 LE since its pretty much the same card just slower.


    I agree with you on this one. Someone need to give these guys a call and tell them how it is. What a load of bs on their naming scheme. I would absolutely call this 7950 SS or LE!
  • 7 Hide
    Anonymous , February 11, 2013 4:11 AM
    where are the frame time benches?
  • 7 Hide
    FormatC , February 11, 2013 4:19 AM
    The frametime thing (in some games) was gone (more or less) with the latest drivers and I think that AMD will handle the memory now a little bit better ;) 
  • 3 Hide
    shikamaru31789 , February 11, 2013 4:27 AM
    If only some other manufacturers were making these, Power Color's cooling solution isn't that good, 37.8 decibels while Gaming is not quiet enough for me.
  • 8 Hide
    EzioAs , February 11, 2013 4:30 AM
    Quote:
    If only some other manufacturers were making these, Power Color's cooling solution isn't that good, 37.8 decibels while Gaming is not quiet enough for me.


    Sapphire has one too, I believe
  • 6 Hide
    shikamaru31789 , February 11, 2013 4:42 AM
    EzioAsSapphire has one too, I believe

    Yeah, I just now noticed it on Newegg. Not sure why I didn't notice it before, based on the reviews it's been on there awhile. Too bad it costs $20 more than Power Color's. Still a good deal even at $260, since this review indicates that it's almost as fast as the much more expensive 7950's.
  • 13 Hide
    FormatC , February 11, 2013 4:45 AM
    It makes sense to include the frametimes if I can show something abormal. If the result is as expected in the tested games... The article was written in the begin of December and published in German first and we all knows what AMD answered about the frametime problems. I'm always using the frametime analysis to proof my benchmark results.

    BTW:
    The Powercolor card was tested a little bit later due the new BIOS. Powercolor has stopped the launch to correct some problems (Club3D and VTX3D were delivered with older BIOSes)
  • 8 Hide
    ricardok , February 11, 2013 5:13 AM
    And please, don't forget to add the Catalyst version you guys are using..

    This time we are without that info. And please say that you did the test with the newest driver.. I fail to see why you guys kept testing with 12.10..
  • 3 Hide
    iam2thecrowe , February 11, 2013 6:18 AM
    should be 7950 Le (light edition). But good card.
  • 4 Hide
    The_Trutherizer , February 11, 2013 6:31 AM
    shikamaru31789If only some other manufacturers were making these, Power Color's cooling solution isn't that good, 37.8 decibels while Gaming is not quiet enough for me.


    I remember about 10-5 years ago 40 decibels was considered whisper quiet.
  • 4 Hide
    JJ1217 , February 11, 2013 7:49 AM
    shikamaru31789Yeah, I just now noticed it on Newegg. Not sure why I didn't notice it before, based on the reviews it's been on there awhile. Too bad it costs $20 more than Power Color's. Still a good deal even at $260, since this review indicates that it's almost as fast as the much more expensive 7950's.


    ehh? I grabbed a Asus 7950 for $230 in *Australia* brand new... I think they're trying to get rid of them since it was the faulty model (Which is easily fixable and since been replaced by the V2 version)..
  • 5 Hide
    sanilmahambre , February 11, 2013 9:02 AM
    SAPPHIRE should have manufactured these Tahiti LE cards with VaporX cooler
  • 2 Hide
    iceclock , February 11, 2013 9:39 AM
    very nice article, at the moment i find the 7870xt edition is one of the best bang for bucks card atm.

    since it gives a good performance for lower cost than 7950 or 660ti

  • 7 Hide
    Anonymous , February 11, 2013 12:20 PM
    I don't understand the conclusion's comments: "if you cannot afford a real 660 Ti this is an alternative." Your benchmarks show this card AHEAD of the 660 Ti in average performance and individual performances, so this card is a better deal even if they cost exactly the same!
  • 4 Hide
    nokiddingboss , February 11, 2013 12:47 PM
    great card but it should have been named 7950 LE. they sure do know how to confuse customers.
  • 5 Hide
    Anonymous , February 11, 2013 1:56 PM
    Id highly suggest buying this baby on NEWEGG as you get BIOSHOCK/TOMB RAIDER Games BUNDLED or BIOSHOCK/CRYSIS 3 BUNDLED for FREE. I'm also under the impression you get the boxed versions.

    Plop these baby's on ebay/amazon and your looking at a 7930-LE $240 for only $140
    DAAANNNG. ^_^
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