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PCI Express - Coming Soon to a PC Near You
Max Romantschuk writes "I've been following the emerging of PCI Express for some time now. PCI Express, previously known as "Third Generation I/O" or "3GIO", is the technology set to replace PCI. PCI has been with us for around ten years now, and is rapidly running out of bandwidth. Last week Anandtech ran an interresting story on PCI Express. The techology has previously been covered by Hexus and ExtremeTech aswell. I feel this technology looks all set to replace PCI, and we really do need some new bus technology to keep up with the bandwidth demands of today's applications. Or is this just yet another way to force us into a new upgrade cycle?"
Or is this just yet another way to force us into a new upgrade cycle?
:)
Or maybe current PCI devices don't support DRM out of the box ? Please upgrade your bus techno, so we can use all this extra bandwidth to transfer huge crypto keys to/from your hardware, just in case you want to play a copyrighted sample on your soundcard
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I'd say a new standard every 10 years is a pretty reasonably upgrade cycle compared to most other PC technologies...
OK, so yes we can probably live with PCI for longer (possibly much longer), but why not introduce a new standard with better potential? It maintains complete backwards compatability with regular PCI components, so manufacturers of harware don't even have to change anything. Of course another issue is motherboard cost, but there will always be new features put into successive motherboard generations that aren't in widespread use yet... like serial ATA, gigabit ethernet, etc. And there will probably be motherboards available for a lower cost without those features as well.
It looks like Linux developers are already working on support. Also, the Inquirer reports that PCI may kill AGP?
Based on the direction in which mass-market computers are moving, the bus that gets exposed to the user is getting somewhat less important. Aside from gamers and tinkerers, and people who manage big servers, how many computer users ever have a need to open up the case?
Ten years ago it was almost a given that at some point, you (or your Computer Guy) had to add or replace one of the cards -- add Ethernet, upgrade the video, whatever. Nowadays, the hardware on-board is more than sufficient, and any of those "special" accessories you get, such as storage drives for your digital camera, or a scanner, or whatever, are more likely than not going to be USB or FireWire.
It's very likely that the mainstream desktop computer is going to move to a slotless "brick" form factor. This would have the side benefit of making it much cheaper. This form factor is available already, but it's not yet cheap because it's still considered a "specialty" unit.
I'd also be happy to see the return of the Commodore 64 form factor -- just shove everything into the keyboard. Plug in your mouse and monitor and Ethernet, and go.
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About the only stuff that has made it into the chipset are cheap soundcards (yes creative is cheap to) and some extremely cheap raid solutions. A lot of other stuff is still in one form or another on the PCI bus. Even if it is not included on a plugin board.
So yes there is a real need for it. Simple example? Raid disks. With striping (multiple disks working together) it is now very easy to saturate the PCI Bus with the cheapest disks.
Same with gigabyte ethernet.
Of course it will be a long time before any real replacement will happen if ever. If I look at some of my old boards on top of the bookclosset I can see it took a long time before ISA was off, and I also see some odd really short slots I never used or seen cards for.
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One high end hard disc delivers 50MB+/s.
One gigabit Ethernet card can do >80MB/s
Together they are limited by PCI.
Now try Raid, TV-Card with PCI-OVerlay, GFX-Cards (Yes, they need a few 100MB/s)...
Plus remember that you NEVER EVER reach 133 MB/S with PCI. Even a single device can be happy to get 110MB with long bursts, and if you have many devices, effective total bandwith is more like 66 than 133 MB/s.
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
You will also need to consider bus efficiency. PCI is something like 60-70% efficient, and PCI-X is about 90%. So 60% of PCI 64/66 is at about 370MB/s. If all your devices happens to run at the same time with your above description you just peaked. However, consumer hardware always lag WAY behind. You are not thinking of enterprise server space where 1GigE is being deployed, fibre channel running at 2GigE, and 10GigE is being developed. Even with PCI-X 2.0 with QDR you may not have sufficient bandwidth eventually. It's a very simple analogy of most home users are still on modem as PCI 32/33, and most of the corporate world is on 10/100Mbps going to GigE as PCI 64/66 -> PCI-X 66-133.
Also, your assumption of 1Gbps peak at 100MB/s isn't quite correct. You have to remember GigE is full-duplex. The theoretical TCP maximum throughput on GigE is about 940Mbps or ~120MB/s. Not that you will ever have traffic full blast both directions but theoretical peak for GigE traffic on the PCI bus would be ~240MB/s.
PCI Express is software compatible. Therefore there wouldn't be any software changes at all to utilize PCI Express. They would be backward compatible and show up looking just like a PCI device. Of course with more features in the PCI Config space just like PCI-X if the software bother to take adventage of them. It really all depends on the OEM vendors on how fast they want to put PCI-E in. But you will see something like back in the days when PCI slowly replacing ISA and now no ISA slots are there anymore.
I scanned the articles checked for anything on this, but didn't find a suitable answer. Will "PCI Express" be like USB, wherein it will support the older gen hardware as well as the newer hardware - or it will only support "Express" PCI devices?
It would be very nice to maintain a PCI port that was capable of faster speeds but still able to run old devices (somewhat like AGP 2x/4x/8x or USB 1.0/1.1/2.0 ramping up, ignoring recent USB developments).
I still remember one of biggest pains in my backside was trying to run PC's that needed an old ISA device (Scanner interface, old ISA SCSI card, special controller card, whatever) which I have heard is a drag on the whole system. Nowadays, I've got only PCI and AGP, though my old but still very good ISA SCSI scanner is still plugged into my 1Ghz Duron (with a single ISA port).
Will we get the best of both worlds? If express supports normal PCI, we can replace the old stuff in a jiffy. Running mixed slots again might be a pain, though.