X-bit labs

NVIDIA NV18/NV28 and AGP 8x Investigation

Category: Video

by FastSite

[ 12/06/2002 | 12:00 AM ]

On September 25, NVIDIA introduced its new graphics chips supporting the AGP 3.0 standard and 8xdata-transfer speed. The chips boasted higher working frequencies as well. But what hides behindthese praised innovations? What are the advantages? Read the review to find out the truth!

Table of contents:

• AGP 3.0: - What's New?
  
• Universal AGP 3.0, Forced AGP 2.0
  
• Closer Look: NVIDIA NV18 and NV28 Graphics Cards
  
• Testbed and Methods
  
• 3D Performance: SiS648 Based System
  
• NVIDIA GeForce4 MX440 with AGP 8x
  
• NVIDIA GeForce4 Ti4200 with AGP 8x
  
• 3D Performance: VIA KT400 Based System
  
• NVIDIA GeForce4 MX440 with AGP 8x
  
• NVIDIA GeForce4 Ti4200 with AGP 8x
  
• Conclusion
  

On September 25, NVIDIA introduced its new graphics chips supporting the AGP 3.0 standard and 8x data-transfer speed.

When naming the chips, the company didn't exert imagination so we have got "NVIDIA GeForce4 Ti4200 with AGP8x" (unofficially known as NV28) and "NVIDIA GeForce4 MX440 with AGP 8x" (NV18). Actually, NV18 and NV28 only differ from NV17 and NV25 by their AGP 8x support. Besides, they also feature higher working frequencies:

• NVIDIA GeForce4 Ti4200 with AGP 8x: 250MHz chip frequency, 128MB 128bit DDR SDRAM working at 512MHz (256MHz DDR).
• NVIDIA GeForce4 MX440 with AGP 8x: 275MHz chip frequency, 64MB 128bit DDR SDRAM working at 512MHz (256MHz DDR).

The increase in the working frequencies is quite significant: "older" GeForce4 Ti4200 based graphics cards with 128MB of graphics memory worked at 250MHz/444MHz (222MHz DDR), while GeForce4 MX440 based cards - at 270MHz/400MHz (200MHz DDR).

In this review we will try to find out the advantages brought about by the increased frequencies and the AGP 3.0 support.

AGP 3.0: - What's New?

The AGP 3.0 standard is the evolutionary development of the AGP 2.0. It's the newest, but regrettably (or, fortunately) the last generation of the AGP standard, which appeared in 1996 and has been steadily developing since then. Intel, the inventor of the AGP, put the full stop in AGP development with this last modification.

The company sees further development of high-performance data transfer buses in serial interfaces and is actively promoting the new PCI-Express standard. Judging by the mess and noise around that new standard, AGP 3.0 is going to give way to faster and perspective data buses soon, despite of all the advantages it may have.

But back to the point. What's so new and impressive about AGP 3.0?

Not delving deep into details, let's list its main differences from AGP 2.0, which are interesting from the bandwidth point of view:

• 4x and 8x data transfer rates support, so the peak bandwidth of the bus in this modes is 1064 and 2128MB/sec, respectively;
• Out of two variants of AGP-transactions (SBA and PIPE), there is only one left - SBA.

  The transaction is a process that includes the creation of a read or write request and the reception of the response to the request. For example, during AGP-texturing, the graphics chip wants to get data from the textures stored in the system RAM and starts bombarding the bus with data-read requests. In response, it gets the requested texture samples.
  In the PIPE mode, the same channel is used for both creating and receiving requests, so the next request cannot be sent until there arrives a response to the pervious one.
  In the SBA (SideBand Addressing) mode, a separate request channel is used, so the requests may be sent before receiving responses to the previous ones. It's clear that the SBA mode uses up the AGP bandwidth more effectively.

• "Long transactions" support (when over 64Bytes are transferred) has been removed. Now, if the graphics chip needs to read over 64Bytes, it has to carry out several transactions;
• "High priority transactions" support has been removed. All the AGP transactions now have "low priority";
• Isochronous mode and isochronous transactions support has been introduced. The regular AGP transactions are now called asynchronous for distinguishing purposes.

  The introduction of transactions of the new type was caused by the fact that there are situations when the bandwidth is not enough and the transaction takes too long, although the AGP bus features high average bandwidth and low latency. This can result in no real trouble in common cases, for instance when working with a 3D graphics card. The worst thing that can happen: some delays of the frames output.
  But the delays accompanied by low buffering may lead to data loss in devices that process streaming data, such as video-capturing cards.
  The AGP 3.0 specification includes a rule that obliges the chipset to effect a set number of specifically marked transactions in a set period of time (1ms), so that it can guarantee no delays and to prevent the bandwidth from falling below a certain level. Transactions like that are called isochronous and can be interlaced with regular, asynchronous transactions. The device that uses isochronous transactions for streaming data transfer can determine the read/write requests ratio in the dedicated channel.
  Isochronous transactions can be used only in 8x data transfer mode. According to AGP 3.0 specs, the AGP bus bandwidth for isochronous transactions cannot be lower than 128MB/sec.

So, there is no doubt that the AGP 3.0 8x mode provides the maximum data-transfer rate. The peak value is 2128MB/sec, which doubles the 1064MB/sec peak value of the 4x mode in AGP 2.0.

Considering the above mentioned things, it's no wonder that the today's leaders in the 3D gaming chips market, ATI and NVIDIA, and also less fortunate SiS and Matrox, accepted the standard at once and released (Matrox is just planning to release) new products with AGP 3.0 and 8x mode support.

Now let's dwell upon some peculiarities in relationships between graphics cards and AGP 3.0-supporting mainboards. You will understand later on, why it is so necessary :).

Universal AGP 3.0, Forced AGP 2.0

The connectors of the graphics cards and slots on the mainboards that support AGP 2.0 and AGP 3.0 may not differ physically, but there are certain "electrical" divergences, of course. Firstly, the connectors of AGP 3.0 supporting devices use contacts that haven't been used before. Secondly, some contacts changed their fucntions. Thirdly, while the high signal in AGP 2.0 equaled 1.5V, it's only 0.8V in AGP 3.0. Fourthly, ...

To cut it short, the graphics card that only supports AGP 2.0 and the mainboard that only supports AGP 3.0 wouldn't work together, in the best case. That's why there are Universal AGP 3.0 and Universal 1.5V AGP 3.0 specifications that add to compatibility of the AGP 2.0 hardware. The possible modes and speeds of graphics cards and mainboards that correspond to different AGP specs, are listed below:

So, I installed the graphics card into the mainboard slot. How does the mainboard recognize the AGP port mode? The system powers up and goes through POST. Then the graphics card and the mainboard that comply with Universal AGP 3.0 and Universal AGP 1.5V 3.0 specs determine the port mode by means of specific contacts on the AGP connector. It is "GC_DET#" contact (Pin #A3), which detects graphics card's ability to work in AGP 3.0 mode (if the card supports AGP 3.0 or Universal AGP 3.0, this contact is connected to the common wire, otherwise it's not connected to anything). The second one is "MB_DET#" contact (Pin #A11), which detects mainboard's ability to work in AGP 3.0 mode (if the mainboard supports AGP 3.0 or Universal AGP 3.0, this contact, like GC_DET#, should be connected to the common wire, otherwise it's not connected to anything).

So, if the both contacts are "grounded" in the graphics card and mainboard, they are checked and then AGP 3.0 is turned on during POST, otherwise - AGP 2.0. Later on, when the system is at work, you can't change the port mode, only the data-transfer rate can be set at either 4x or 8x for AGP 3.0 and 1x, 2x or 4x for AGP 2.0.

When we tested NV18 and NV28 based graphics cards with the mainboard supporting AGP 3.0, the AGP 3.0 mode is enabled without any options. This fact turned out a real nuisance during the tests.

By changing data-transfer speeds, we could see the real advantage of the transfer via AGP bus in test results. In other words, the advantage of 8x speed compared to 4x speed. But 4x in the AGP 3.0 mode and 4x in the AGP 2.0 mode are different things as AGP 3.0 forces all the new AGP 3.0 features, no matter what data-transfer rate has been set. And it means that it would be incorrect to compare 4x and 8x speeds in AGP 3.0, as the effective bandwidth in 4x AGP 3.0 may differ from 4x AGP 2.0, that is, from the mode supported by NVIDIA NV17/NV25 based graphics cards.

Nevertheless, in spite of this "incorrectness" we will compare the graphics cards performance in AGP 3.0 mode at 4x and 8x speeds.

Another way to estimate the advantages of AGP 3.0 and 8x data transfer speed is to compare NV17/18 and NV25/28 by setting equal core and graphics memory frequencies. But again, this method lacks accuracy, as we will compare different graphics cards, with different PCB designs, different BIOS, memory timings and different graphics chips…

Although we did carry out such a test, bear in mind the above mentioned stipulation.

The only correct way to figure out the actual advantages of AGP 3.0 8x seems to be like that. We should somehow make NV18/28 based cards work in a Universal AGP 3.0 mainboard in both modes: AGP 3.0 and 2.0.

Do you think that it is impossible? Not at all :).

AGP 3.0 specs say that if one party - the graphics card or the mainboard - doesn't support AGP 3.0, the AGP 2.0 mode will be enabled instead.

So it's simple: if we insulate the GC_DET# contact in the graphics card connector, the mainboard will think that the card doesn't support AGP 3.0. Similar: if we insulate the MB_DET# contact in the AGP slot, the graphics card will check it and find that the mainboard doesn't support AGP 3.0. As a result, if we insulate both contacts, then both: graphics card and mainboard, will enable AGP 2.0 mode (of course, if they both comply with the Universal AGP 3.0 or Universal AGP 1.5V 3.0 specs, i.e. are compatible with the "old" AGP 2.0 standard).

The insulation was made with tiny pieces of scotch tape.

The reference card based on NV28 (NVIDIA GeForce4 Ti4200 with AGP 8x) will serve as an example. That's the way its AGP connector looked like before taping the contacts (the MB_DET# and GC_DET# contacts are marked with arrows):

   

When taped up, the MB_DET# and GC_DET# contacts looked like that:

The card is ready for testing in the AGP 2.0 mode: the MB_DET# and GC_DET# contacts are insulated just like in AGP 2.0 graphics cards, where they are not laid out at all. You can see it in the following snapshot of the NVIDIA GeForce4 Ti4600 based graphics card:

   

So, after making clear what and how we are going to test, let's go over to the "heroes of the occasion": the new GPUs from NVIDIA with AGP 8x support and the graphics cards based on them.

Closer Look: NVIDIA NV18 and NV28 Graphics Cards

New NVIDIA chips support AGP 3.0 and 8x data transfer rate that is why their engineers had to re-design the layout a bit. The NV18 (GeForce4 MX440 with AGP 8x) based reference card differs from its predecessors most notably:

   

As you can see in the pictures, the graphics card features BGA memory chips, just like NVIDIA GeForce4 MX460. However, this time all the memory chips are placed on the front side of the PCB.

The GPU is cooled by a passive heatsink. Under the heatsink we find a chip marked as: "MX440-8x" meaning "NVIDIA GeForce4 MX440 with AGP 8x".

The GPU works at 275MHz frequency.

The graphics card is equipped with 64MB of 128bit DDR SDRAM graphics memory from Samsung with 3.6ns access time.

The graphics memory of NVIDIA GeForce4 MX440 reference card with AGP 8x works at 512MHz (256MHz DDR).

The card is equipped with a DVI and D-Sub connector, as well as with a composite TV-In/TV-Out connector. The output onto the TV-set is performed by the TV-Out unit, which is integrated into all GeForce4 MX chips. The external SAA-7114H chip from Philips is responsible for video capturing and decoding.

The NVIDIA GeForce4 Ti4200 with AGP 8x based graphics card doesn't differ much from the cards that follow NVIDIA GeForce4 Ti4200 reference-design:

   

The reference card is equipped with a rather out-dated cooler, similar to what they used in NVIDIA GeForce3 based cards. Under the unassuming cooler we saw a new NVIDIA chip: GeForce4 Ti4200 with AGP 8x:

The GPU frequency here is 250MHz.

The graphics card is equipped with 128MB of 128bit DDR SDRAM memory from Samsung with 4ns access time.

The graphics memory frequency is 512MHz (256MHz DDR). According to the manufacturer's specs, the maximum working frequency for 4ns chips is only 500MHz (250MHz DDR). So, the graphics memory here works at an irregular frequency. To put it short, it's overclocked. We may only wonder what prevented NVIDIA from using a bit faster graphics memory chips in their card :).

NVIDIA GeForce4 Ti4200 with AGP 8x reference card is equipped with a DVI, D-Sub and TV-Out connectors. The traditional for the Ti4200 family Sil164CT64 chip from Silicon Graphics controls DVI-output, while the SAA 7104E/V1 chip from Philips forms the video signal for TV-Out.

By the time we worked on the review, the NV18 based graphics cards had hit the stores already. So, we took a mass piece instead of the reference one. The first NV18 based card we got into our lab was a solution from Albatron.

A few words about the Albatron GeForce4 MX480 graphics card.

The card is shipped in a stylish looking retail package:

It includes the graphics card, the user's manual, two CDs with drivers and WinDVD, an S-Video-to-RCA adapter and an RCA cable:

The card follows the design of the NVIDIA GeForce4 MX440 reference card supporting AGP 8x:

   

The card features the NVIDIA GeForce4 MX 440-8x GPU and 64MB of 128bit DDR SDRAM from Samsung with 3.6ns access time:

   

The chip and memory working frequencies comply with those recommended by NVIDIA: 275MHz/512MHz (256MHz DDR) respectively.

The cooler on the GPU deserves a closer look: it covers not only the graphics core, but also the graphics memory chips. It's not that the memory chips in such a graphics card required any special cooling, or the GPU needed such a big cooler, but this cooling system does look impressive anyway.

As for the name of the card, it is not the best thing Albatron could do, actually. The number "480" in it may confuse the customer into thinking that this graphics card would work faster than NVIDIA GeForce4 MX460, which is not true. It's sad, but another graphics card makers may follow Albatron's example.

However, Albatron GeForce4 fully complies with NVIDIA's reference card in terms of frequencies and design and arouses no complaints about its functioning, which is just what we need now :).

Testbed and Methods

The most popular AGP 3.0-supporting chipsets today are SiS648 for Intel Pentium 4 and VIA KT400 for AMD Athlon XP.

So, the benchmarks were run on two systems:

The SiS648 based testbed was configured as follows:

• Intel Pentium 4 2800MHz CPU;
• ASUS P4S8X (SiS648) mainboard;
• 512MB PC2100 CL2.5 DDR SDRAM by Samsung;
• IBM DTLA 305030 HDD.

The VIA KT400 based testbed was configured as follows:

• AMD Athlon XP 2700+ CPU;
• ASUS A7V8X (VIA KT400) mainboard;
• 512MB PC2100 CL2.5 DDR SDRAM by Samsung;
• IBM DTLA 305030 HDD.

We used the following software:

• Detonator 40.52 for Windows XP;
• Windows XP:
• DirectX8.1;
• Quake3 Arena v. 1.30;
• Serious Sam: The Second Encounter;
• Unreal Tournament 2003 v.2107.

The higher data-transfer speed of AGP may lead to performance growth in "extreme" modes: in high resolutions, with turned-on full-screen anti-aliasing and anisotropic filtering.

In this case, some textures may not fit into the local graphics memory and the GPU will have to use AGP-texturing, that is, take samples from textures that are stored in system RAM. Quite naturally we expect that doubled AGP bandwidth in 8x mode will improve the results significantly.

On the other hand, we shouldn't expect these situations to happen often. Game developers do their best to avoid AGP-texturing, as the 4x AGP bandwidth (1064MB/sec) is much lower than the graphics memory bus bandwidth. For example, with 128bit DDR SDRAM working at 400MHz (200MHz DDR), the peak graphics memory bus bandwidth makes 6400MB/sec.

Besides the data, transferred via the AGP bus during the textures loading or AGP-texturing, the GPU also receives the descriptions of polygons vertexes. Transferring the polygon data via the AGP bus in low resolutions may take not so little time compared with what the drawing of these polygons on the screen takes. In this case, the higher AGP bus bandwidth would also positively impact the results.

Taking all this into consideration, we decided to test the graphics cards in both low and high resolutions as well as with enabled full-screen anti-aliasing and anisotropic filtering.

We used the following settings in the games.

Quake3 Arena:

32bit screen and textures color depth. Maximum graphics quality settings. Tri-linear filtering and texture compression enabled.

Serious Sam: The Second Encounter:

32bit screen color depth. "Quality" graphics quality settings.

Unreal Tournament 2003 v.2107:

Default graphics quality settings.