PCI - AGP - PCI-E

[Maximilian]

I dont get how PCI-E can be so much faster and more advanced than PCI, it looks the same, minor differences and AGP simply looks like a PCI slot painted brown. Is there some underlying technical thing im missing here?

Almost every other bit of hardware has changed the way it looks in the past 10 years, except maybe hard drives, my 4gb wd from 97 looks like my 80gb. But since PCI came and replaced ISA, which looks a lot different from PCI, all the slots have looked the same.

Would it be correct to assume that PCI is the baseline tech, AGP is a souped up PCI slot, basically with a faster bus, and PCI-E is a souped up AGP slot with an even faster bus and 16X capability (not sure to what the 4x, 8x, 16x refers to exactly though).

 

[MattCE]

Originally posted by: Soviet
Is there some underlying technical thing im missing here?

Yes

 

[Maximilian]

Originally posted by: MattCE

Originally posted by: Soviet
Is there some underlying technical thing im missing here?

Yes

Then enlighten me.

 

[AndyHui]

Physically, they are quite different. More pins, for one thing.

For a bit of a primer on PCI Express and other buses, take a look at something I wrote.

 

[Maximilian]

Originally posted by: AndyHui
Physically, they are quite different. More pins, for one thing.

For a bit of a primer on PCI Express and other buses, take a look at something I wrote.

Thanks, that was insightful. The whole PCI and PCI-E thing consists of a lot more than simply the slot, which is generally what i thought, i knew that it mustve connected to somthing but i didnt think it was all that important.

Also the VL-Bus.... i never knew that was an actual bus. A long time ago when i was like 7, i had a 486SX, i didnt really know much about tech, being 7 and all, and one day i found this set of floppys. They said VL-BUS DRIVER on them, i was like "WOW VIRTUAL BUS DRIVER!! NEAT!!" I though i would get to drive a bus around and pick people up etc etc, i put the disks in and it mustve booted from them or somthing, i dunno but i ended up wiping windows 3.1. Now i know what those disks were *actually* for

 

[randay]

uh, yeah, there should be hundreds of articles on the net that will help you with that.

They may look alike, but they are not. Simply because of the fact that if they were physically identical, you would have people plugging agp cards into pci slots and turning thier computers into smoke machines. They have different pins amounts, configurations, are keyed differently, run at different speeds, use different technologies, and all that good stuff.

 

[icarus4586]

The physical connector is one of the least relevant things to consider when looking at bus technologies.
PCI and AGP are parallel buses - they send data many bits per clock. AGP is faster than PCI, but it also allows the graphics card more direct access to the main memory and the CPU, since it isn't sharing the bus with other devices. AGP also uses "sideband addressing," which means that address lines and data lines are separate. AGP is also pipelined.
PCI-E a serial bus. 1x, 2x, 4x, 8x, and 16x PCI-E has a totally different meaning than it does for AGP. AGP runs at a 66MHz clock rate, and the multiplier has to do with how frequently data is sent. In PCI-E, these refer to how many serial links are going to the slot. 1x has one link, 4x has 4, etc. Because it is serial, PCI-E can run at much higher frequencies while also simplifying motherboard design.

 

[BassBomb]

isnt pci e serial interface? allowing for full duplex transfers hence 16x vs the 8x of agp

 

[Aluvus]

Originally posted by: BassBomb
isnt pci e serial interface? allowing for full duplex transfers hence 16x vs the 8x of agp

As stated right above your post, the x16 (not 16x) used to refer to some PCI-Express slots has nothing to do with AGP 8x. If you would like to see a capacity comparison, try here.

As also stated right above your post, yes, PCI-Express is in fact serial.

 

[BassBomb]

true

what i meant was, serial basically is full duplex while parallel is half... so they didnt really change the amount of transfers going to the slot, it just became serial... thats why its called 16x PCIe when AGP was 8x

that was my take on it

 

[Aluvus]

Originally posted by: BassBomb
true

what i meant was, serial basically is full duplex while parallel is half... so they didnt really change the amount of transfers going to the slot, it just became serial... thats why its called 16x PCIe when AGP was 8x

that was my take on it

No, PCI-Express's by-x system and AGP's multiplier system are totally unrelated. They are describing completely different things.

PCI-Express x16, etc. get their name from how many lanes they use. AGP 8x, etc. get their name from how many transfers they execute per clock cycle. They are not connected.