Processor and other speed questions

[Cazadum]

I'm planning on building a decent gaming computer. I have been doing some research but there are still a few things I am unclear about.

First off, how important is bus speed? When comparing 2 processors, is bus speed a good spec to compare? I read something that the actual bus speed that a processor communicates with peripheral hardware is the bus speed divided by the number of cores. Is that true?

When choosing RAM, should the RAM's bus speed match that of the processor? So if a dual core processor had a bus speed of 1333 Mhz, the ideal RAM speed would be 1333/2= 666.5 Mhz? And just to be clear, the RAM would be called

Also, is there any way to tell if a video card is overkill and my system won't utilize it to its full potential? And conversely is there a way to tell if my system can handle a more powerful video card?

Any input will be greatly appreciated.

 

[Mondoman]

Number of cores doesn't affect the (front side) bus or the memory bus; it just allows 2 (or 4) program segments (or "threads") to run at the same time. This helps when you're running multiple programs at the same time, or with programs that are specially written to use multiple threads in parallel.

The main number to look at is the core speed of the CPU. FSB speed, cache amount, memory bus speed and so forth will have only minor additional effects on performance (up to maybe 10% or so).

As for RAM, you want to have the memory bus datarate match the FSB datarate, since all data going between the RAM and CPU has to go through both the memory bus and the frontside bus. Assuming you have installed RAM DIMMs in pairs, just take the FSB datarate (e.g. 1333MHz), divide by 2 (no matter how many cores), and that will give you the memory bus speed to run. For a 1333MHz FSB datarate, 1333/2 = 667, so you would run the memory bus at DDR2-667.

When not gaming, the model of the video card doesn't matter. For gaming, the better the video card, the faster the frame rate (or the better the details). In practice, your video card will never be overkill -- the better the video card, the better your gaming performance.

 

[Kraynor]

The main number to look at is the core speed of the CPU. FSB speed, cache amount, memory bus speed and so forth will have only minor additional effects on performance (up to maybe 10% or so).

Just one point about the cache amount - Try to get a CPU with a decent cache. A system will be somewhat bottlenecked with too small a cache (just look at the Pentium D). It doesn't make that huge a difference but it's an easily avoidable problem so why run into it?

Basic rule is that you want 2 to 3 MB of cache per core in a quad core, 3 to 4 MB in a dual core (simply because you can and it doesn't throw the price up that much, relatively speaking). Just as a point of interest, the Pentium D line mostly only has 512KB per core, while some of the more 'expensive' Pentium D chips have 1MB per core.


And yes, you'll see the best performance gains with a 1:1 ratio beween your FSB and Memory Bus, unless you spend an absolute fortune for high-end DDR3 RAM. DDR2-667 will serve you fine with a 1333 MHz FSB.

 

[rtfm]

Slap a q6600 (oc slightly) with 4gb ddr2 and a 4870 (or a 4850 if you game at lowish resolutions of 1280x1024 and below) and decent mobo and you can't go wrong, you will be a happy gamer for a long time to come

Don't get too deep into thinking about it, just buy and enjoy. Oh, don't forget a good quality brand psu - it will save you a lot of headaches

 

[Kraynor]

Q6600 is awesome all right, have one myself and wouldn't change it. Best bang for buck chip around, and can hit 3.2 GHz quite easilly on aftermarket cooling.

 

[Cazadum]

Thanks for the help guys.

I've been told that a dual core is better than a quad for gaming. Is there any truth to that?

 

[zenmaster]

Dual vs Quad is a tough question.

At the same speed, Quad will be better in all cases.
However, Duals tend to be clocked higher than Quads.
The result is that Duals are faster in programs that do not make sure of more than two cores, which is most at this point.

When building a gaming system, start with a lower end chip such as the E7200 and then flesh out the rest of the parts. This can be OC'd to proivde sufficient power. Then once the rest of the system is set, if you still have funds left over, consider upgrading the CPU. The E8500 and Q6600 are popular options in the next range up.

You will find threads with 100s and 100s of responses arguing which is better. They key will be to check the games you may like to see if they support quads at this point.

 

[Cazadum]

As for RAM, you want to have the memory bus datarate match the FSB datarate, since all data going between the RAM and CPU has to go through both the memory bus and the frontside bus. Assuming you have installed RAM DIMMs in pairs, just take the FSB datarate (e.g. 1333MHz), divide by 2 (no matter how many cores), and that will give you the memory bus speed to run. For a 1333MHz FSB datarate, 1333/2 = 667, so you would run the memory bus at DDR2-667.

So if I had a Q6600, the FSB rate would be 1066/2 = 533 and not 1066/4 = 266.5? And I read that for DDR2 the speed should also be divided by 2, so from using your example above wouldn't the best RAM be DDR2-1333? Also, how does the bandwidth factor in? Would the total bandwidth for a Q6600 be 1066*8 = 8528 Mb/s? If that is correct, should the total bandwidth for memory only go up to that value, even if the motherboard supports more sticks of RAM? So that if DDR2-1333 is (1333/2)*8 = 5336 Mb/s, it would be pointless to add another stick of DDR2-1333 since 2*5336 = 10672 > 8528, and I'd be better off getting a second stick of slower RAM (since it's cheaper)?

Thanks Zenmaster for the cpu advice, I think that is what I'll do.

 

[Dekasav]

Really, you can ignore the FSB entirely. Just grab one or two sets of 2Gb DDR2 800 RAM and call it good. But add ram in pairs, and use the same kind. (Either 2 sticks of 1Gb, 4 sticks of 1Gb, or 2 sticks of 2Gb.)

 

[Mondoman]

So if I had a Q6600, the FSB rate would be 1066/2 = 533 and not 1066/4 = 266.5?

No, the stock FSB for a q6600 is a 1333MHz datarate. However, many people overclock it by raising the FSB, with a 1600MHz FSB datarate being pretty much the practical maximum for this CPU.

And I read that for DDR2 the speed should also be divided by 2...

Sort of -- to match the FSB datarate and memory bus datarate, run the memory bus at 1/2 the FSB speed. Thus, a 1333MHz FSB datarate matches that of a memory bus run at DDR2-667. Since the memory bus has 2 channels (DIMMs installed as pairs) running in parallel, 2x667 = 1333.

..., so from using your example above wouldn't the best RAM be DDR2-1333?

No, see above.

...Also, how does the bandwidth factor in?

"datarate" accounts for bandwidth.

Remember also that all DIMMs installed on a MB have to run at the same speed (the memory bus speed), which may or may not be automatically set to the rated speed of the DIMM modules.

 

[Kraynor]

Basically the speeds are all multiplied... it's complicated but I'll try to lay it out simply.

A CPU has a clock speed, and a multiplier. The clock speed multiplied by the multiplier gives the end result.
In the Q6600's case, it has a clock speed of 266 MHz, and a multiplier of 9, giving a nett result of 2.4 GHz.

The FSB speed then is the CPU's clock speed multiplied by 4, in the Q6600 it's 1066 MHz, but as stated above some people overclock it to 3 GHz (which is very easy), resulting in a 333 MHz CPU clock speed, and a 1333 MHz FSB speed.

Most newer CPUs come with a FSB speed of 1333 MHz anyway through a multiplier of 8.

Where the CPU:RAM ratio comes into it then is in the name - DDR2... that is Double (or is it Dual) Data Rate. The clock speed of RAM is the rated speed divided by 2. With DDR2-667, it has a clock speed of 333 MHz. Look familiar? It's the same as your 1333 MHz FSB CPU's one!

That's where the extra performance comes from - both pieces of kit work in syncronisation.

 

[Cazadum]

A CPU has a clock speed, and a multiplier. The clock speed multiplied by the multiplier gives the end result.In the Q6600's case, it has a clock speed of 266 MHz, and a multiplier of 9, giving a nett result of 2.4 GHz.

What is this multiplier? Is it simply 9 "units" pumping at 266 MHz for a grand total of 2.4 GHz, or is it something built into the circuit that can be set to multiply the base frequency by a certain factor?

The FSB speed then is the CPU's clock speed multiplied by 4, in the Q6600 it's 1066 MHz, but as stated above some people overclock it to 3 GHz (which is very easy), resulting in a 333 MHz CPU clock speed, and a 1333 MHz FSB speed.

Is the FSB speed always the CPU clock speed multiplied by 4, or is the 4 specific to the processor or the number of cores?

Where the CPU:RAM ratio comes into it then is in the name - DDR2... that is Double (or is it Dual) Data Rate. The clock speed of RAM is the rated speed divided by 2. With DDR2-667, it has a clock speed of 333 MHz. Look familiar? It's the same as your 1333 MHz FSB CPU's one!

So DDR2-XXX isn't actually using a frequency of XXX. The XXX is what a single data rate would have to be at to match the cycles/second of the dual rate?

Basically the speeds are all multiplied... it's complicated but I'll try to lay it out simply.

Feel free to get complicated if you have to. I have a decent knowledge of circuits and I'm trying to bridge the gap to the application. If you could get all nuts and bolts on me, I'd be extremely grateful, and I appreciate all the help everyone has given me so far.

 

[Kraynor]

It's complicated to the point I don't fully understand the specific circuitry, but I know enough to get by.

Don't know what a multiplier is all I know is what it does for the chip as a whole. It's also part of Intel's SpeedStep technology, the multiplier in your CPU drops to a lower integer when less power is needed, sticking with the Q6600 it goes from 9 to 6... which is also the main cause of 90% of the 'My CPU isn't running as fast as it should!' threads here on the THG Forums.

Also, as far as I know FSB is always divided by 4, and you're right about DDR to the best of my knowledge.