AGP vs. PCI slots for Video cards

[ebane67]

Whats the REAL difference between cards that use PCI slots vs. cards that use AGP slots?  Are PCI video cards harder to find?  Are PCI cards slower in some way?  Whats the deal?

[AgtFox]

PCI is for sure slower and AGP has different multipliers (up to 8x).  I'm not sure of the technical breakdown, but AGP runs at a higher bus speed than PCI and allows a quicker route to the processor than PCI does.

Now there is PCI Express, which is supposedly going to be faster than AGP or already is faster.

[ebane67]

Yeah, I have heard of the xpress thingie.  I have read about some PCs that use it, but they only had expandable PCI slots, no AGP.  This kinda scared me away from them - From what I have gathered, this type of setup is bad news if you are a gamer.
Anyone have any more details about this?

[ravenvii]

PCI Express is going to replace both AGP and plain PCI (and it's successor, PCI-X, but that's a whole another post). So running cards in SLI mode is now possible and easier - since you can use any of the PCI Express slots for your card.

That's how I understand it.

[egrudzin]

Here's the skinny on AGP as I understand it:
-AGP runs at a faster bus speed than PCI, I think 66Mhz whereas PCI is only 33Mhz.
-The 8X, 4X refers to how fast it can write. 1X is 256 MB/s, 2X is 512 MB/s and so on.
-AGP can also read and write from the main system memory as if it were additional memory on the card.  This is advantagous if the Vid card runs out of its own RAM it can suppliment this with main system memory.  I'm not sure how many programs make use of this as the system memory operates at drastically slower speeds than what is on the card.

For the next 6 months at least I imagine AGP will probably be widely used for video cards. It will get phased out for PCI express as will the standard PCI.

Dell is already shipping PCs with only PCI and PCI express (no AGP) and according to them by next year they will have PCs with only PCI express.  According to the Dell representative from my University they believe hardware manufactures will begin to jump on the PCI express bandwagon pretty soon to support the new PCs.  Hope this clears things up a bit...

[Geezerone]

AGP will be dead soon.  Nvidia's new graphics cards first come out in PCI-e format and then followed with an AGP version (if ever).

The AGP bus is really a specialized version of the PCI bus that runs faster and has additional "instructions" that pertain to graphics acceleration.  You can use it as a faster PCI slot, many older server motherboards did just that.

Unfortunately, Intel is doing the same kind of thing with their new (upcoming) chipsets.  The 16x PCI-e port is dedicated for graphics (with additional "instructions" to accelerate graphics), while the 4x and 1x PCI-e slots are more general purpose.

[ebane67]

OK, so my NEXT question is...If I am looking to buy a new PC by the 1st of next month, should I look for one with an AGP slot or one of the new xpress set ups?

[AgtFox]

OK, so my NEXT question is...If I am looking to buy a new PC by the 1st of next month, should I look for one with an AGP slot or one of the new xpress set ups?

I don't know what others think, but it's a tough choice honestly because PCI Express today is kind of a middlepoint between AGP and what is coming out later.  The new PCI Express will obviously be a big jump from what is currently available.  It's a coin toss honestly at this point.

You can relate it to the release of SATA drives.  At first they didn't work so well, but after a couple motherboard revisions and manufacturers understanding it more, the technology became better.

We're kind of in a transition time right now...is that how the rest would characterize it?

[Geezerone]

I would agree with you to a certain extent AgtFox.  Todays PCI-e cards (video cards at the moment) certainly are no better than the corresponding AGP version, but it's not the buses fault.

Todays CPU chipsets (like Intels northbridges) usually provide a 16x PCI-e bus (that's 16 lanes wide in PCI-e terminology) for the graphics port on the motherboard.  Each lane is capable of 2.5 Gbps so the 16x port is capable of 40Gbps of throughput, that's 5GB/s!!!  In contrast a single Gigabit ethernet port would only connect to a 1x PCI-e port.  I believe an AGP port is around 2 Gbps.

So todays bottlenecks in performance are in the CPU, the memory interface, and the graphics processing chips, not in the bus.  I thought I read that one or more sites had tested the current PCI-e video cards in different PCI-e slots (some were 16x, some 4x, and some 1x) and they did not show that significant of a difference between them.  So obviously the problem is with the video card and not the bus.

What this really tells us is the motherboard is pretty much future proof (especially with Intels announcement that no 4GHz CPUs are going to be done, ever) and that video cards still have plenty of room to get really, scary fast.  So my prediction is that you will be replacing your motherboard because of new (multi-core) processors rather than graphics card upgrades.

Of course, I will not be upgrading to a PCI-e system until my brand new ATI x800pro ViVo card becomes an obsolete piece of crap.  :cry: