ATI Mobility Radeon HD 3850 vs ATI Mobility Radeon HD 3870 X2

ATI Mobility Radeon HD 3850

The AMD ATI Mobility Radeon HD 3850 is a slower clocked desktop HD 3850 and manufactured in 55 nm. It supports DirectX 10.1 in hardware and also features the Avivo HD video engine to help the CPU decode videos. The card is intended to be used in large laptops.

The performance of the graphics card is between the GeForce 8700M GT and the 8800M GTS. The ATI Mobility Radeon HD 4650 of the successor generation performed similar but with a much lower power consumption. Therefore, the performance should be sufficient for DirectX 9 games in medium to high details (see games list beyond).

The RV670 chip has 64 5-dimensional unified shaders with 16 ROPs, 16 TMUs, and 32 TAUs.

The Avivo HD video engine helps the cpu in decoding HD videos (MPEG-2, H.264, VC-1). The HD 3850 houses the UVD+ (Unified Video Decoder) that is capable of decoding MPEG-2, H.265/AVC, and VC-1 nearly fully. The UVD2 in the HD 4000 generation is capable of full bitstream decoding and two video streams can be decoded at once (which UVD+ can not).

Compared to desktop graphics cards, the HD 3850 is similar to the Radeon HD 3850 but features a much lower clock speed, leading to a worse performance.

The power consumption of the HD 3800 series lies between 35-55 Watt.

ATI Mobility Radeon HD 3870 X2

The Mobility Radeon X3870 X2 combines two Mobility Radeon 3870 graphics cards (on MXM boards) onto one laptop in Crossfire (CF) mode. Therefore, the combination has a power consumption of roughly both cards combined. While the total available VRAM has been doubled, the effective VRAM is actually half of the combined total as each card must store the same textures and data onto their own respective onboard VRAM chips.

Depending on the application, the performance of the Radeon X3870 X2 about 0-40 percent above a single Mobility HD 3870 and is even a bit above the GeForce 8800M GTX SLI solution. Most, if not all, DirectX 9 games can run fluently in high resolutions and detail settings. More demanding DirectX 10 games, such as Crysis,  will only run acceptably well on medium to high detail settings with lowered resolutions.

As with all multi-GPU solutions, the HD 3870 X2 may suffer from a phenomenon known as micro stuttering. See here for an overview of the term and why it happens.

Hardware features that can be found on a single Mobility HD 3870 have been preserved in the Crossfire combination. As a result, the dual GPU setup can take advantage of Avivo HD in order to aid the CPU in decoding videos.

The power consumption of the Mobility 3870 X2 can be up to 110 Watt when including the MXM boards and VRAM chips. AMD specifies that the HD 3800 series can draw up to 33-55 Watt per card.