Despite the similarity between the 3850 and the 3870 the two cards use quite different form factors. The 3870 is a double-slot design that vents air through the mounting bracket as per the X850, X1800, X1900 and HD 2900, while the 3850 is a single-slot card that keeps the hot air inside the case much like an X1950 Pro or, indeed, an 8800 GT.
Ready for four-card CrossFire X...
The most obvious technical difference between the two models is that 3870 has 512MB of GDDR 4 memory and 3850 uses 256MB of cheaper, slower GDDR 3.
The 3000 series chips employ a PCI Express (PCIe) 2.0 interface which is handy if you have an Intel X38 motherboard. However, the extra bandwidth of the new interface won’t yield any immediate advantage. Think in terms of removing a potential bottleneck in performance and then lift your sights to the prospect of CrossFire X in January when we will have the prospect of up to four graphics cards working on the same image. It sounds like it might be marvellous but we’ll reserve judgement until we’ve seen the thing in action.
...but you won't see it until early 2008
Intriguingly, both the 3850 and 3870 use a single six-pin power connector to supply extra power despite the fact that PCIe 2.0 can deliver 150W through the graphics slot. However, most graphics cards will look for an extra power connector, so you need a six-pin power connector even if it isn’t strictly necessary.
How They Compare
| HD 3870 | HD 3850 | HD 2900 XT | |
| Transistors | 666m | 666m | 700m |
| Process | 55nm | 55nm | 80nm |
| Stream Processors | 320 | 320 | 320 |
| Core Clock | 775MHz | 670MHz | 740Mhz |
| Memory Clock | 2.25GHz | 1.66GHz | 1.65GHz |
| PCIe Version | 2.0 | 2.0 | 1.1 |
| UVD | Yes | Yes | No |
The 2900 XT didn’t have a UVD because the core was too large to allow the inclusion of unnecessary extras, so your PC had to decode HD-DVD and Blu-ray movies with brute force courtesy of your CPU. With the 55nm die-shrink AMD has freed up a stack of space and reduced the cooling requirements to such an extent that the 3870 runs as quietly as the benchmark GeForce 8800 GT so a noisy processor cooler would be a real intrusion during movie playback. Enter stage left the UVD, although movie buffs should note that the new graphics chip employs the same HD audio processor as the 2900 so it’s HDMI 1.1 rather than 1.3, which kisses off the prospect of Dolby TrueHD and DTS Master HD.
COMMENTS
You try to buy one....
I have been looking for 2 weeks now for one of these in the UK and its been like trying to buy rocking horse s**t... And the same goes for any 8800 GT's... Are they all making one a day or something? I did find one place that did have 5... placed my order and it was out of stock.... jeez....
Huh?
Whats with the "Bias Alert" nonsense? The FACT is, any 8800GT card other than the slowest speed 8800gt, is an OVERCLOCKED card.
They reviewed the correct card, as the 3870 can also be overclocked, which it wasn't in this review... and the 3850 was never intended to compete with the 8800GT as it has less memory. The 8800GT also has many reports of heat problems when overclocked, along with noise. Unlike the 3870 which doesn't.
re drivers
Couldn't agree more, with the point about drivers. Nvidia are now the preferred graphics card vendor for Linux systems like Ubuntu because of the ease of driver installation and compatibility with features.
Re: Look Ma, no main memory left!
Actually, modern cards don't map all of video ram into PCI space. Typically they only expose the first 128 or 256Mb. In practice the CPU never accesses video ram directly because it's painfully slow (very high latency). All data is transfered via the card's DMA engine.
This is ignoring the fact that even 32-bit x86 cpus have had 36-bit physical addressing for years (though not all of that is available for PCI devices), and a quad-card system is kinda dumb if you have a meaty CPU and buckets of ram to back it up.
Look Ma, no main memory left!
I'd like to see what happens when you combine 4 x 1Gb versions of this card on a 32 bit system (where the GPU is memory mapped).
See http://www.dansdata.com/askdan00015.htm for a round-about explanation.
