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First Looks At PCI-X, BTX, New Chipsets, And More
rsrsharma writes "AnandTech has some early bird Computex 2004 coverage up its sleeve. Included are the first pictures and partial specs of nVidia's NV45, the PCI-X (PCI-eXpress) successor to the 6800 Ultra, and ATI's PCI-X cards. Also shown are Intel's new 9xx line of chipsets and LGA-755 motherboards, BTX form factor (the successor to ATX) motherboards, and much more. I'm definitely looking forward to this stuff." Update: 06/01 01:08 GMT by T : Several readers have pointed out that PCI-X properly stands for "PCI Extended" rather than "PCI Express."
As usual there's some confusion between PCI-X (64bits PCI up to 133mhz) and PCI express which is a serial bus. Please call that PCI-E or whatever!
If you don't feel like clicking through a hundred pages, use the "print" link instead.
This is actually the first I heard of BTX, so I immediately flipped to the last page and had a look at the board. I have to say that the thing that bothers me the most about it, is the apparent lack of expansion slots. I only saw one slot, which was probably PCI-X?
I sincerely hope that this does not mean the end of expansion cards. Because if it DOES, I am just going to say goodbye to Windows, and get a Mac. It defeats the main advantage of a PC if I can't upgrade whenever I see fit.
I'm assuming you're talking about NICs (I for one need quite a few PCI slots myself for the thing). The newer tower computers (early 2005) will probably have lots of PCI slots, one AGP slot, and one PCI-X slot. Small-form-factor computers will have one of each.
It also kinda irks me when I see that PCI-X will not be in any way compatible with older PCI cards. They ought to change the name. This is a good technology, don't get me wrong; this speed is needed for both the newer video cards and gigabit and 10-gigabit network cards of the future, but when people try to stick in the old PCI cards that their cable/DSL provider gave them into those slots and find that they don't fit, they'll be making a call to the manufacturer wondering why a PCI card doesn't fit in a PCI-X slot.
A bureaucratic nightmare, indeed. Change the name, Mr. Industry, or you'll regret ever inventing tech support.
It should be noted that Mr. Anand mostly focuses on the gaming industry. I knew him back when he was in high school and he only looked at new technology if it would help him get his game on. So for mainstream society and the people who use game consoles instead of PCs, this isn't necessarily news.
PCI-X is a 133mhz bus which is backward compatible with PCI and PCI66.
PCI-Express is a system bus but is more of a networking protocol using high-speed differential signaling (like DVI and SATA) as the physical layer.
PCI-X and PCI-Express are similar only in name (and some similarities in how "config space" is handled). They are really two radically different things.
- PCI-X: 64bits PCI up to 133mhz
- PCI Express: Serial bus, a replacement for AGP (mostly), and for graphics cards (at the moment). What I accidentally called PCI-X (PCI eXpress)in the article. From other articles I've read, it looks like it'll be used for all cards eventually. Although I still think this acronym makes more sense than PCI-E, I guess it'll confuse some people who have actually heard of PCI-X before. I have this wierd feeling that the industry is gonna call PCI Express PCI-X now (it sounds way cooler).
Some other info on PCI Express:- There can be different sizes of slots. All the graphics cards use x16 size slots, while it looks like most other types of cards will use x1 size slots.
- It will eventually become ubiquitous like PCI
- More information in this article.
I'm sure I got something wrong, feel free to correct me.Am I missing something? They've replaced the standard ATA-IDE connectors with Serial ATA connectors, gotten rid of all of the PCI slots, but for some reason kept the FDD drive connector and the parallel port? Most newer motherboards support booting from USB flash device. As for the parallel port, there aren't many devices being sold today that use them and there are parallel-USB adapters available for those who want to use their old printers.
I know this is a pico-ATX board so it's understandable that the PCI slots were removed for space-saving purposes, but if a pico-ATX enclosure can't fit an extra PCI card, why leave room for a floppy drive?
Yep, they are usually to make different traces either equidistant or to introduce necessary delays. Another reason to use non-straight paths is to avoid RF interference and induced current between PCB layers. Also hard bends in a trace can often lead to leakage and singaling problems so you might need two smooth curves to avoid a single hard corner.
There are 4 boxes to use in the defense of liberty: soap, ballot, jury, ammo. Use in that order. Starting now.
I've never designed a high speed digital board before, but I guess it's to compensate for the transmission line effect.
;-)
Let's pick a number. Say 500MHz. Depending on dielectric constant of the PCB substrate, thickness, etc. a ball park figure for the speed of a signal propagating along one of those traces is around 70% the speed of light, so 2.1E+9 m/s. That makes the 500MHz signal have a wavelength of about 4.2m. Now, consider a 20cm trace. That shouldn't be unrealistic on a video card, if you actually followed one around on the PCB, it could be longer.
That trace has delayed the signal by 17 degrees, or 0.05 of a wavelength, which may or may not be significant. If we have the 64 data lines in a 64bit bus all different lenghts, you can see that different bits are going to "arrive" at different times.
Transmission line theory is a black voodoo art, where you can do all kinds of neat stuff like "create" reactive components and make matching transformers (impedance matches) or filters (different goal, same method) on your high frequency PCB just by making a carefully calculated sudden change in track width, plus the necessary "stubs"...
This all very over-simplified, but yeah, the squirly bits are to keep them all the same length (my guess). I'd be very worried if digital circuits needed impedance matching transformers made out of microstrips
PCI Express is software compatible with PCI and PCI-X, but the physical connection is different. There are already specifications available for PCI Express-to-PCI/X bridge, so you need'nt worry about your "legacy" PCI devices becoming useless after PCI Express' adoption.