At some point in the future, I’ll be upgrading my wife’s computer. I’ve built before, so I’m not worried about that, but…poking about, I’ve seen the new AMD 64-bit processors. I understand that, as of right now, there’s few applications made to take advantage of this, but in the future there will be more, and it is backwards compatible.
Is there any advantage to this?
Also, I’ve noticed that there are two different types - Socket 754 and Socket 939. What’s the difference, and what are the advantages?
I have a socket 754 Athlon 64 2800+ in my computer right now, and am pretty knowledgable about processors.
To take full advantage of the 64 bit instructions, you need a 64 bit operating system, like various Linux distros; WindowsXP 64 bit edition is in beta right now, and should be available by the end of the year. Some applications don’t gain anything by running in 64 bit mode; other do - for example, in the video encoding I have done, 64 bit mode is generally 10%-15% faster.
The other advantage of 64-bit is the increased address space; a 32 bit processor has 4 gb of address space, (and since Windows normally takes half of that), that makes the maximum amount of RAM you can have 2 GB. 64 bit systems have many terabytes of address space. This isn’t a big deal right now, as even a heavy gamer like myself gets by fine with a single gig of RAM, but the need for RAM is ever increasing.
Also note that my processor still runs pretty dang fast in 32 bit programs, and performs excently in Doom 3 & HL2.
The difference is the number of pins on the chips - Socket 754 chips have 754 pins, and Socket 939 have, you guessed it, 939 pins, and dual channel memory support, and price.
Basically, Socket 754 chips can communicate one stick of memory at a time, while 939 chips use those extra pins to communicate with 2 sticks of memory at once, doubling memory bandwidth. In the real world, this doesn’t make much of a difference - maybe 3%-5% performance gain. Socket 754 chips are the budget line, and are a bit cheaper & the mobo’s tend to be cheaper as well, though as of late, it isn’t that much difference.
Another factor to consider is that all of the PCI-Express boards I have seen for Athlon 64s are for the socket 939 chips. If you don’t know what PCI-Express is, well, it is the new bus system set to replace the PCI/AGP bus used in current computers.
My reccomendation for the new computer would be to go with the slightly more expensive Socket 939 route, and a PCI-Express board (with the nforce 4 chipset).
Thank you, RandomLetters - that answered about all of my questions (including one I was saving for another thread - gotta up that post count! 
), and well answered 'em, to boot.
I just built a new system, and I used a socket 939 Athlon 64 3500+ combined with an nforce4 chipset motherboard (PCI Express).
The nforce4 motherboards are hard to come by (or were a few weeks ago) but this combo seemed the most “future-proof” to me.
The system is smokin fast, and the motherboard has been rock-solid stable. Color me satisfied!
I also just built a system using an Athlon64 (as did D_Odds, who will likely be along shortly). I chose the 3500+, which is a Socket939 model. I went with the 90nm version, as it runs cooler.
The chip is really, really nice. I don’t have a 64-bit operating system to throw at it, so I can’t speak to that… but it handles Half-Life 2 and City of Heroes without any problems at all.
One thing to be aware of if you’re building and concerned about noise is that motherboards are starting to employ active cooling. In the case of the Asus SLI Deluxe board I have, that means an 8000 rpm screamer of a fan on the motherboard. A passive cooling solution arrives here in The Lab on Wednesday, and Anghammarad will be getting a trip downstairs to have his motherboard silenced. Annoyingly enough, this means removing the motherboard, which will require me to half-disassemble my system. It’s worth it, but I recommend doing the switch before building the system if you can.