Details leaked: ATI Radeon 4800 gets 480 stream processors

Posted by Theo Valich

Chicago (IL) – Next month will be more important for AMD’s graphics division than any other month of this year: The company is set to release the (RV770) 4800-series of graphics cards, including the models 4850, 4870 and 4870 X2. While the launch is still very much a secret, TG Daily was able to receive details and the specifications of the new cards – which will put ATI back into the ring with Nvidia.

The product launch will be significant not just because of the availability of chips, but also because of the fact that AMD/ATI is returning to a true six-month refresh cycle of its graphics products. Looking back, the 2900/3800 series was not really a six-month refresh, since the 2900XT was eight months late. The Radeon 3800 series was launched in November of 2007 and since the Radeon 4800 is pretty much set for a May 2008 launch (cards went into production in March), the ATI team has returned to its traditional cycle. There is a good chance that the acquisition troubles have been digested and new products will be surfacing in a more predictable fashion from now on.

Specifications: 480 stream processors, 800+ million transistors

Let’s have a look at the general specifications of the Radeon 4800 series, which is based on the RV770 graphics processor. The new GPU has 480 stream processors or shader units (96+384), 32 Texture units (up from 16), 16 ROP (same as 2900/3800), a 256-bit memory controller and native GDDR3/4/5 support (expect GDDR3 and GDDR5 memory versions of RV770 cards).

The transistor count has jumped from 666 million in the RV670 to more than 800 million transistors in the RV770.

The manufacturing process has been carried over: TSMC is producing the GPUs in 55 nm (the process itself is called 55GC).

The Radeon 3800 series had a serious flaw called texture low fill-rate, which was addressed by ATI with an increased number of TMUs (Texture Memory Unit) from 16 to 32. The specifications indicate that 16 TMUs can address 80 textures on the fly, which means that 32 units should be able to fetch 160 in the RV770: This should allow the new GPU to catch up with Nvidia’s G92 design. However, the G92 has 64 TMUs that were enabled gradually (some SKUs shipped with 56), resulting in a fill-rate performance that beat the original 8800GTX and Ultra models.  

ATI’s RV770 will be rated at a fill rate of 20.8-27.2 GTexel/s (excluding X2 version), which is on the lower end of the GeForce 9 series (9600 GT: 20.8; 9800 GTX: 43.2 9800 GX2: 76.8).

New for the 4800 series is AMD’s decision to split the clock of the GPU and shaders, following a move that Nvidia made with the GeForce 8800: Back then, the shaders were clocked at 1.35 GHz, while the rest of the chip ticked at 575 MHz.

Read on the next page: GPU and memory clock speeds, Pricing


The Radeon 4850 will debut with a GPU clocked at 650 MHz, while the shader array will be clocked 850 MHz. The 4870 has an 850 MHz core and a 1050 MHz shader clock. The fill-rate is closely tied to the GPU clock: The 4850 sports a fill-rate of 20.8 GTexel/s (32 TMU x 0.65 GHz), while the 4870 achieves a 27.2 GTexel/s (32 TMU x 0.85 GHz) performance.

The RV770 GPU is equipped with a 256-bit memory controller (512-bit for the Radeon 4870 X2: The R700 represents just two RV770 GPUs slapped together). 4850 GDDR3 models will come with 256 MB or 512MB of GDDR3 memory, clocked at 1.14 GHz (2.29 GTransfer/s), resulting in a memory bandwidth of 73.2 GB/s. 4850 GDDR5 versions integrate 512 MB of GDDR5 memory clocked at 1.73 GHz (3.46 GT/s), supporting a bandwidth of 110.5 GB/s. 4870 GDDR5 models will get 1 GB of memory clocked at 1.94 GHz (3.87 GT/s), achieving a maximum bandwidth of 123.8 GB/s.

Flagship dual-GPU 4870 X2 cards will include 2048 MB of GDDR5 memory clocked at 1.73 GHz. The Radeon HD 4870 X2 will be introduced at a later date (and could see spec revisions).

You may be wondering why ATI decided to go with "odd clocks" for the video memory part and the answer may surprise you: According to our sources, AMD is no longer clocking the cards towards performance, but towards power efficiency instead. This happened first with the Radeon 2900XT (which was bleeding lots of current) and continued with the 3800 series.  

Overclockers should have no problem reaching the magic 4 GHz mark for the GDDR5 memory (1.94 to 2.0 GHz), but that, of course, would break the sub-150 watt thermal-envelope these cards were designed for. More than ever before we can envision AMD and add-in-board vendors offering a “Radeon HD 4870 TDP - Saves you $$$ on Electricity Bills!" or a "4870 Lots of Horsepower and Power Hungry" edition of these cards.  

The 4850 in fact is in a 110 watt power envelope (the 4850 256MB GDDR3 is a sub-100 watt card). There is, by the way, a big difference in power consumption between GDDR3 and GDDR5 versions. 512MB GDDR5 memory will consume 34.5% less power than a model with 512MB of GDDR3 memory.

As you can guess, a 110 watt power envelope means that 4850 boards will have a single-slot cooler, while the 150 watt part (4870) should be available as single-slot part as well (from at least one partner, 1-slot vapor chamber part). Most of manufacturers will, however, offer dual-slot cooling for the 4870.

4870 X2 is an interesting version. AMD did not send out any specs to its partners and it is expected the board will be a bit more than just a 3870 X2 two RV770 GPUs. ATI is said to be making some changes, most notably in the PCI Express department (3870 X2 is actually a PCIe 1.1 part). The product will keep the aggressive pricing in place, and, according to our sources, will scale much better than 3870 X2.

The 4850 256MB GDDR3 version will arrive as the successor of the 3850 256MB with a price in the sub-$200 range. The 4850 512MB GDDR3 should retail for $229, the 4850 512MB
GDDR5 will set you back about $249-269. The big daddy, the 1GB GDDR5 powered 4870 will retail between $329-349.

When it will become available the 4870 X2 will hit the market for $499.

Our sources indicate that the launch is only weeks away, so expect your usual hardware sites to feature dozens of reviews of 4850 and 4870 with GDDR5 memory, since this memory type will be a hot topic in months to come.

Editor’s note: Due to popular demand (see comments section of our first story ), the opening picture of this article was indeed an RV770 GPU picture. Enjoy.