64bit processing..

jesus_thats_gre

This is a brilliant article on AMD's processor.

http://www.anandtech.com/cpu/showdoc.html?i=1815

Quote from page 5:

The features of x86-64, whose implementation in Opteron is called AMD64, are pretty straight forward:

1) backwards compatible with current x86 code
2) 8 new 64-bit general purpose registers (GPRs) as well as 64-bit versions of the original 8 x86 GPRs (only available in 64-bit long mode, described below)
3) SSE & SSE2 support along with 8 new SSE2 registers
4) Increased memory addressability for large dataset applications (only available in long mode, described below)
5) Solid performance in current 32-bit applications with support for 64-bit applications going forward, a good transitional processor

With the ability to run current x86 code as well as future x86-64 code, you can guess that the K8 has two operating modes; they are called "legacy" and "long."

In legacy mode, the K8 will run all native 16 or 32-bit x86 applications, the processor basically acts just as a K7 would.

Things get interesting in "long" mode where a 64-bit x86-64 compliant OS is required; in this mode, the K8 can either operate in full 64-bit mode or in compatibility mode. Full 64-bit mode allows for all of the advantages of a 64-bit architecture to be realized, including 64-bit memory addressability. One of the major features of the K8 architecture is the fact that the number of general purpose registers is doubled when in x86-64 mode, and thus this feature is also taken advantage of in full 64-bit mode.

Compatibility mode gives you none of the advantages of a 64-bit architecture on the application level, as it is designed for running 32-bit apps on a 64-bit OS (hence the name compatibility); The extra registers and 64-bit register extensions are ignored in this mode.

sceptre

Originally posted by jesus_thats_gre
Compatibility mode gives you none of the advantages of a 64-bit architecture on the application level, as it is designed for running 32-bit apps on a 64-bit OS (hence the name compatibility); The extra registers and 64-bit register extensions are ignored in this mode.

Of course.

That's why it's called compatibility mode. If it addressed the extra 32 registers in this mode it wouldn't be very "compatible" now would it.

BabyEater

There shouldn't be a major price difference between the 3200 Athlon64 and the 3200XP . As they have the same PR rating the 64bit will be a bonus that won't be very usefull until people write the code to take advantage of it. Unless a lot of 64bit CPU's are sold not very many people are going to write code to take advantage of it.These Athlon64's will be a single channel chip. The AthlonFX will be dual channel .
X-Bit labs say the Athlon64 3200 will be about $400.
The Athlon FX will be about $700
The best time to buy the new range of these CPU's would be when it is moved to .09 micron as it will probaly have DDR2 support and PCI express and should have some overclocking headroom.

jesus_thats_gre

Of course.

That's why it's called compatibility mode. If it addressed the extra 32 registers in this mode it wouldn't be very "compatible" now would it.

Thats brings me back to my original point. For the home user, i.e. us, there is currently very little benefit to the 64 bit features of the processor. The primary benefits seem to be the improved architecture. When running 32 bit applications, the Opteron is effectively the same as the K7/Athlon processor.

The_Bullman

The Opteron is not effectively the same as a K7 . The main difference is the on die memory controller which helps in both 32bit and 64 bit computing as the latencey's are dramatically reduced.

spooky donkey

Originally posted by jesus_thats_gre
So Intel are never going to release a 64 bit processor aimed at the desktop market?
http://www.boards.ie/vbulletin/showthread.php?s=&threadid=110646&perpage=20&pagenumber=2

I did read a news article yesterday that intel do not expect 64 bit processors to enter the home PC market for a few years to come. Perhaps they mean when we all get a pc with 4 GIGS of ram as standard, how far away will that be?

sceptre

Originally posted by spooky donkey
Perhaps they mean when we all get a pc with 4 GIGS of ram as standard, how far away will that be?

It'll be a few years before 4 gigs becomes standard. "Standard" seems to be 256 now, it was 64 about two years ago (roughly). If we assume (again really roughly) that standard memory doubles about every year (assuming no price increases) then it'll be 3-4 years.

Obviously for gamers it's higher but they're not "standard" buyers.

(I'm taking "standard" to mean the regular offers in the newspapers, which is as good an assessment as any)

jesus_thats_gre

Fair enough. I have made my opinion known and am happy to leave it that.

astrofool

btw, i didn't mean that the opteron just had 64bit tacked on, if you're implying that the onboard memory controllers in particular seem to greatly enhance performance, and I believe that intel's 800bus was a response to that, earlier roadmaps had shown a 667 bus, but amd going dual ddr redresses that.

But as a simple example, hlds when recompiled with a 64bit compiler recieved a 30% performance boost, all other factors being equal. The advantage of basically having more data on chip in registers is great. XP 64-bit should be faster performing than the current 32bit XP. Basically it's meaning that AMD could clinch a performance advantage that puts hyperthreading to shame, if people start using it. The other bells and whistles on chip only add to whats looking like a great package at the moment, Intel's response will be interesting because they will HAVE to go 64bit in the near future. And worse for them, they'll have to go 64bit the way AMD envisaged x86-64 and not the way they'd like it. Interesting times indeed.

Of course athlon 64 could easily flop due to buggy motherboards, or poor performance, but then the cpu market will be doomed to slow down, and recieve features when intel feels it's made maximum money off it's old line of chips.

BabyEater

As far as i remember Intel can use the Yamhill which they developed to counter the Athlon 64 if the Athlon 64 becomes too succesfull this adds extensions like the Athlon64.
Correct me if i am wrong as i haven't heard about Yamhill in a long time so they might have stoped its progress.

JustHalf

Originally posted by astrofool
btw, i didn't mean that the opteron just had 64bit tacked on, if you're implying that the onboard memory controllers in particular seem to greatly enhance performance, and I believe that intel's 800bus was a response to that, earlier roadmaps had shown a 667 bus, but amd going dual ddr redresses that.

If I remember correctly, Intel originally intended to go to 800MHz, then shifted to 667 then back to 800 again.

po0k

667 is what they use for the Xeons now afaik.

On-die memory controllers have been standard with all the "proper" 64-bit processors for quite a while, eg. Alphas, Sun Ultra SPARCs etc.

makes perfect sense tbh.

This leaves one qustion, will it be PCI express or AGP on the boards?

astrofool

AGP.

PCI Express will be next years big thing.

And the next step was 667mhz for a long time, they never switched from one to the other. You've got to wonder how far they can push the qdr bus of the p4, it's already double what it started at, the p3 ended it's life at that stage, as is the k7 athlon