ATI Radeon HD 4890: Playing To Win Or Played Again?

Building A Radeon HD 4890

Architecturally, the RV790 graphics processor is identical to RV770. The vital specs haven’t changed one bit. It’s still a 55 nm component, though transistor count is up just slightly to approximately 959 million transistors (from 956 million). The GPU is still made up of 800 stream processors, 40 texture units, and 16 ROPs. It still sports a 1 GB GDDR5 frame buffer on a 256-bit memory bus, too.

Where it differs most is clock speed—on its core and memory bus. Stock Radeon HD 4870s employed a 750 MHz engine and quad data rate memory running at 900 MHz. This new offering cruises at 850 MHz with 975 MHz GDDR5 memory.

In order to get those elevated frequencies, ATI had to do some work to the GPU’s core. In short, the RV770 consistently had issues clocking beyond a certain point—a fact that was evident in many of our System Builder Marathon overclocking attempts, which generally fell short at the same frequency range.

The company’s engineers went in looking for slow electrical paths and re-wired them in such a way that they wouldn’t inhibit faster frequencies. Physically, the GPU is fractions of a millimeter larger due to additional capacitors that clean up power to the chip. But it remains the same ol’ design popularized mid-2008. As you can see from the table above, clock-for-clock RV770 and RV790 perform nearly-identically clock-for-clock.

Swipe to scroll horizontally
Header Cell - Column 0 Radeon HD 4870 X2Radeon HD 4890Radeon HD 4870GeForce GTX 285GeForce GTX 260 Core 216
Manufacturing Process55 nm TSMC55 nm TSMC55 nm TSMC55 nm TSMC55 nm TSMC
SPs1,600 (2 x 800)800800240216
Core Clock750 MHz850 MHz750 MHz648 MHz576 MHz
Shader Clock750 MHz850 MHz750 MHz1,476 MHz1,242 MHz
Memory Clock900 MHz GDDR5975 MHz GDDR5900 MHz GDDR51,242 MHz GDDR3999 MHz GDDR3
Frame Buffer2 x 1 GB1 GB1 GB / 512 MB1 GB896 MB
Memory Bus Width2 x 256-bit256-bit256-bit512-bit448-bit
ROPs2 x 1616163228

Not surprisingly, the 4890 card itself is easily mistaken for a Radeon HD 4870. They’re the same length; they both employ dual-slot coolers and the same dual-DVI plus video output configuration. Subtle differences set the two cards apart, giving away the fact that these two boards are indeed based on different GPUs.  And despite the slight increase in load power consumption as a result of the 4890’s higher clock speed, ATI still gets away arming the card with two six-pin auxiliary power connectors.

As of right now, ATI doesn’t have plans for a Radeon HD 4890 X2 variant, as it likely wouldn’t offer much more than a Radeon HD 4870 X2. And the chip’s extra full-load power consumption would create additional heat that’d need to be cooled.


The principal benefit from moving from HD 4870 to HD 4890 would, in our minds, be overclocking headroom. Stock-to-stock, you’re looking at a 100 MHz frequency increase. However, right out of the gate, ATI’s board partners will be shipping juiced models running a 50 MHz-faster core clock. According to AMD, the new GPU layout should be capable of going even faster than that.

The driver’s Overdrive sub-routine now offers a maximum frequency of 1 GHz, suggesting ATI is fairly comfortable with its enthusiast customers running at that speed. Rather than push our card that high and run the risk of misrepresenting performance with a hand-picked sample, however, we ran our HIS Radeon HD 4890 Turbo sample at its stock 900/975 MHz speeds and compared it to the reference clocks ATI is officially launching.

Upping the core clocks to 900 MHz is good for gains between five and 10% at 2560x1600. One of these factory-overclocked boards undoubtedly enhances the value of ATI’s Radeon HD 4890 versus the 4870 1 GB. However, there will undoubtedly be an additional price premium over the reference cards, too, softening the worth of that extra performance to some degree.

Chris Angelini
Chris Angelini is an Editor Emeritus at Tom's Hardware US. He edits hardware reviews and covers high-profile CPU and GPU launches.
  • mbbs20
    overclocking ?
  • eklipz330
    i usually don't bitch and moan about them not having enough test gpu's, but i'd really like to see that sapphire 2gb 4870 up there, seeing how its in the same price range as the 4890...

    any of these cards would suffice for me, 1680*1050 does save you a pretty penny
  • ravenware

    It seems to overclock well and outpaces the 275.

    The stalker results seem odd from both review sites. But stalker is glitchy.

    If priced right this should be a decent addition to the 4x series.
    It holds its own against the 275 and in certain games the 285.

    Perhaps sapphire will release a dual card.
    The 4850x2 they released performed extremely well.
  • megamanx00
    The 4850X2 is absent to compare to I see. Still nice to finally see a review of this thing. Nice gains over the 4870.
  • eklipz330
    Stalker: Clear Sky benchmarks are fairly new in our graphics card reviews, even if the game itself isn’t particularly fresh.Let us know what you think of this one in the comments section. At the very least, it’s a beautiful looking game.

    any benchmark is welcome i suppose

    too bad price goes up exponentially for minimal improvements... the 4890 will be about %50 more than the 4870
  • cangelini
    Both the 2 GB card and the 4850 X2 are exclusive to Sapphire, and neither has been sent over. Nevertheless, we'll be following up with SLI/CrossFire scores in the near future and I'll see if either of those two solutions might be lined up for that story.
  • eklipz330
    cangelini, you are the man.

    just thought i'd let you know. this article was very well written, and you said everything i was thinking including the pricing. too bad you have to go to the other article to refer to gtx275 comparisons. regardless of that, gj
  • cangelini
    Thanks Ek. Truth be told, both companies pulled their launches in, allowing about a week to get the testing/writing done. Usually that's pretty tight for one new launch. Two is a little rougher. But hopefully there was enough cross-linking between the pair to convey the right messages.
  • mbbs20
    a good read...hardocp has a good one up as well
  • ifko_pifko
    I'll post it here as well as in the GTX275 review:
    Summing all the framerates is just nonsense. ;-) The games with higher fps will weigh more than the others.