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Review: Nvidia Gainward GeForce GT 640 Rev 2 (GK208)

by Tarinder Sandhu on 20 August 2013, 17:00

Tags: NVIDIA (NASDAQ:NVDA), Gainward

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A new GeForce for entry-level systems

Multiple GT 640 GPUs

Though the tech press' attention rarely wavers from looking at high-end, aspirational components that often grace wish lists, the mundane truth is that selling in volume is king. Most readers cannot justify spending £800 on a GeForce GTX Titan or £500 for a Radeon HD 7990, but, with many being gamers at heart, often look for the cheapest, most cost-effective method of obtaining more performance.

Just the other week we took a look at a Radeon HD 7730, priced at around £60 and offering a visually better gaming experience than on the very best integrated graphics (IGPs) bolted to the latest CPUs from Intel and AMD. The direct comparison from Nvidia, GeForce GT 640, was conspicuous by its absence, though there's good reason for that.

Nvidia sees the GT 640 as an add-in card for a very wide variety of systems. Creating great scope for deployment means the GT 640, unlike other GPUs, is available in a multitude of flavours - some are retail, others are OEM, and there are a few in-between.

Take a peek at most retailers' listings and you'll simply see Brand 'X' GeForce GT 640 alongside a basic specification and, obviously, a price. But the devil really is in details, as Nvidia is transitioning retail cards from the GK107 to the GK208 die.

What's in a name?

A shift in die usually means a bump in specification, with the new part running faster due to optimisations at manufacturing partner TSMC. This time, however, there are considerable changes afoot for the budget GT 640 and it's worth delving into a table to tease out the finer details.

GPU GeForce GT 640 Rev 1 GeForce GT 640 Rev 2 Radeon HD 7730
Radeon HD (5)6670
Codename GK107 GK208 Cape Verde LE Juniper XT
DX API 11 11 11.1 11
Architecture Kepler Kepler GCN VLIW5
Process 28nm 28nm 28nm 40nm
Transistors 1.3bn 1.02bn 1.5bn 716mn
Die Size 118mm² 79mm² 123mm² 118mm²
Processors 384 384 384 480
Texture Units 24 16 24 24
ROP Units 16 8 16 8
GPU Clock (MHz) 900 1,046 800 800
Shader Clock (MHz) 900 1,046 800 800
GFLOPS

691

803.3

614

768

Memory Clock (MHz) 1,782 5,010 4,500 4,000
Memory Bus (bits) 128 64 128 128
Max bandwidth (GB/s) 28.5 40.1 72 64
Power Connectors None None None None
TDP (watts) 65 49 47 66
GFLOPS per watt 10.6 16.1 13.1 11.6
Street Price £60 £60 £60 £50

Analysis

For the sake of clarity and exposition we'll call the GK107 - which is, by far, the most popular retail die - the GT 640 Rev 1 and the newer, smaller, leaner GK208 as GT 640 Rev 2: cards based on this die, and indeed in this review, are now slowly coming to market.

Let's compare the GT 640s. Scan halfway down the table and you'll wonder what Nvidia is up to. The die is fabricated on the same 28nm process and is around 25 per cent smaller. This insight tells us the newer GPU is bereft of some of the key building blocks of GPU performance, and consultation of the table describes how the GK208 has fewer texture-units and only half the back-end ROPs. Pixel fillrate, in particular, is significantly lower on the new model.

Yet Nvidia realises that, with modern games, shader throughput and memory bandwidth are the key performance-defining metrics. The GK208 cranks up core/shader speed to 1,046MHz and, with an identical number of processors, has a solid increase in GFLOPS. Decreasing die size can also be accomplished by adopting a narrower memory bus, which is half the width of the GK107's, but the new memory configuration of 1GB GDDR5 at 5GHz ensures that overall bandwidth is actually 40 per cent higher - the older card uses slow DDR3 memory in comparison.

The original GK107-based GT 640 is, for the target market, a wide, slow, medium-sized GPU. Nvidia's use of higher frequencies and optimised layout play well in the sub-$100 market and, on paper, should give AMD's nascent Radeon HD 7730 a good fight.

Our advice for anyone seeking a 'new' GT 640 is to pay close attention to the specifications as most retailers tend to list the frequencies, if nothing else.

Gainward's retail card

We have a Gainward GK208-based GeForce GT 640 in for review today, and while this editorial is more focussed on the transition of dies for the entry-level discrete card, it makes sense to have a peek into a partner's implementation.

A card that consumes just 49W at full chat doesn't need an overbearing cooler. Gainward does the right thing by going for a low-profile PCB. The 1GB framebuffer is provided by two chips that sit just to the right of the GK208 GPU.

Outputs, too, are sensible, with dual-link DVI-D, HDMI and D-Sub (via ribbon cable). We'd like to see a passively-cooled version offered as an alternative, because, while certainly not loud by any stretch of the imagination, the fan can just about be heard in our ultra-quiet test system.

Known by the model number 426018336-2913 - do look it up if unsure - and costing around £60, let's now hop on over to the benchmarks.