Early this year NVIDIA launched two solutions based on overhauled 55nm GPUs, but AMD did not respond promptly with its own products. However, rumors of an improved "super RV770" had been circulating through the web for a long time already. The company didn't seem ready to produce improved GPUs at that time. But in early April AMD finally announced its new graphics card based on the improved RV7x0 GPU.

The new solution from AMD -- RADEON HD 4890 -- is based on the overhauled RV790 GPU. Its differences from RV770 will be described later, and now we're interested in card's improved performance. RADEON HD 4890 works at higher frequencies than HD 4870, and its direct competitor is NVIDIA GeForce GTX 275 that was launched on the same day.

The reviewed graphics card is somewhere between RADEON HD 4870 1GB and HD 4870 X2 in terms of performance and price (it looks like everybody, even AMD, has already forgotten about HD 4850 X2), but closer to the former, of course. The new product is positioned against GeForce GTX 275, which corresponds to the recommended price of $260. HD 4870 with 1GB of video memory ranks lower, while HD 4870 X2 and the rare HD 4850 X2 stand much higher.

According to AMD, the key objective of the new GPU was to lead the Upper Mid-End price range. But we know that the improved RV790 is just a modified RV770, designed for higher clock rates and performance. There are no other changes, the process technology is the same (well, almost the same), all features have been preserved, the architecture hasn't changed. It's just that when a rival releases solutions based on the newer process technology, it's necessary to do the same to keep the market position. Even if the novelties are not completely new.

If you don't know about the RADEON HD 4800 (RV770) architecture, you can read all details in our baseline review. This architecture is actually an overhauled R6xx with lots of modifications to improve its functionality and performance. Detailed information about the unified architectures R7xx/R6xx, exemplified by previous solutions, can be found in the following articles.

• ATI RADEON HD 4870 512MB
• ATI RADEON 4850 512MB
• ATI RADEON HD 2400XT/2600PRO/2600XT (RV610/630)
• ATI RADEON HD 2900 XT (R600)

We proceed from the assumption that our readers are already familiar with the RV7xx architecture. Now we'll examine specifications of the new RADEON HD 4800 graphics card based on the overhauled RV790 GPU. The theoretical part won't be long, as the GPU itself hasn't changed much, and we have already examined its architecture. Let's take a look at the graphics card specifications.

RADEON HD 4890

• Code name: RV790
• Process technology: 55 nm
• 959M transistors (versus 956M in RV770)
• Unified architecture with an array of common processors for streaming processing of vertices and pixels, as well as other data
• Hardware support for DirectX 10.1, including new Shader Model 4.1, geometry generation, and stream output
• 256-bit memory bus: Four 64-bit controllers supporting GDDR3/GDDR5
• Core clock: 850 MHz
• 10 SIMD cores, including 800 scalar floating-point ALUs (integer and floating-point formats, support for FP32 and FP64 in compliance with IEEE 754)
• 10 enlarged texture units supporting FP16 and FP32 formats
• 40 texture address units
• 160 texture fetch units
• 40 bilinear filtering units that can filter FP16 textures at full speed, trilinear and anisotropic filtering for all texture formats
• Dynamic branching in pixel and vertex shaders
• 16 ROPs supporting antialiasing with programmable sample patterns (over 16 samples per pixel), including FP16 or FP32 formats of the frame buffer. Peak performance is up to 16 samples per cycle (including MSAA 2x/4x and FP16 buffers), 64 samples per cycle in Z only mode
• Writing results up to eight frame buffers simultaneously (MRT)
• Integrated support for two RAMDACs, two Dual Link DVIs, HDMI, HDTV, DisplayPort

RADEON HD 4890 specifications

• Core clock: 850 MHz
• Unified processors: 800
• 40 texture units, 16 blending units
• Effective memory frequency: 3900 MHz (4*975 MHz)
• Memory type: GDDR5
• Memory: 1024 MB
• Memory bandwidth: 125 GB/sec
• Maximum theoretical fillrate: 13.6 gigapixel per second
• Theoretical texture sampling rate: 34.0 gigatexel per second
• Two CrossFireX connectors
• PCI Express 2.0 x16
• 2 x DVI-I Dual Link, 2560x1600 video output
• TV-Out, HDTV-Out, support for HDCP, HDMI, DisplayPort
• Power consumption: up to 190 W (60 W when idle)
• Two-slot design
• Recommended price: $259

Minor modifications of the GPU (to be described below) allowed AMD to design a faster solution, ranking above RADEON HD 4870. The new graphics card is faster. Besides, the HD 4890 consumes much less power in idle mode than its predecessors. We should thank much lower clock rates in 2D mode than in RV770.

As usual, we pay attention to memory volume and product name. Unlike previous solutions from Series 4800, the HD 4890 is not equipped with 512MB of memory, there are no such models anymore. The only modification offers 1GB of video memory, the optimal choice for Upper Mid-End cards, because 512 MB is not enough in some situations, while 1 GB of memory will suffice for a long time.

The name of the new graphics card has gone through logical changes. AMD rolled out a slightly accelerated card (versus the HD 4870) called HD 4890. This change of a model number makes sense to users. It clearly indicates that the card is faster, but it belongs to the same family.

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