Overclocking with P4 (800FSB)

[philsymonds]

Hi folks
Got a problem:  Got great BIOS that allows me to O/C my 2.8 P4 800FSB by 10, 20 or 30%.  However, when i do, the RAM drops from dual channel (2x200Mhz=400Mhz), to single channel.  This effectively reverses any advantage gained by the CPU O/C.  Any ideas?  Someone suggested using a matched pair of Corsair PC3500 RAM sticks, but this seems a little ott.
Phil

[4_Series_Scania]

I think you need to buy faster RAM, I've oc'd my 2.6c to 3.4ghz, lost the dual channel but still noticed an improvement in 3D Mark 2003 & 2001, either way, actual "game play" in FS,CFS or Battlefield 1942 / Desert combat Nascar 2003 etc etc etc was visually no better but my cpu was considerably hotter.....

In short, its back to standard and fast enough for my uses..... (or in other words, I could'nt afford any faster than PC400 when I upgraded!  ::) )

Buy some PC500 DDR and watch that p4 take off....  8)

http://www.corsairmicro.com/corsair/xms_proseries.html

http://www.overclockers.co.uk/acatalog/Online_Catalogue_Corsair_65.html

Regards,

Paul.

[congo]

Why is the ram dropping dual channel mode?

Are you guys leaving the Ram to Auto-config using the SPD?

I've been manually dropping my Ram speed way back, so when I overclock the FSB, the ram just comes up to it's normal speed, isn't that what you are supposed to do? Or does dual channel drop out anyway?

[philsymonds]

?

[4_Series_Scania]

Why is the ram dropping dual channel mode?

Are you guys leaving the Ram to Auto-config using the SPD?

I've been manually dropping my Ram speed way back, so when I overclock the FSB, the ram just comes up to it's normal speed, isn't that what you are supposed to do? Or does dual channel drop out anyway?

I'm assuming its 'cos I'm pushing the RAM beyond its design limits? dunno really, in a nutshell, with PC400 DDR, my machine isn't much quicker overclocked. I've "borrowed" from a mate, some PC500 DDR, the speed jump was considerable but still not worth

[congo]

Hi again philsymonds,

I just re-read your first question, and it appears you aren't clear on what "dual channel mode" is.

You get your "virtual" 800mhz front side bus speed because it's kind of a 4x multiplier of an actual FSB speed of 200mhz.

A P4 cpu performs similar trickery through it's technologies, and gains a massive apparent speed increase through it's mutipliers.

At stock clocking, your RAM actually runs at 200mhz, (the actual FSB speed), but it's DDR or DUAL DATA RATE, which makes it "virtually 400mhz" , it's not truly running at 400mhz, it reads the data twice in a single clock cycle, once on the voltage rise, and again on the voltage fall.

This DDR RAM running at 400mhz is specified with a maximum rating for the ram module, ie. PC3200, meaning it's desinged to run at a maximum speed of 400mhz DDR , or a 200mhz maximum bus speed.

Some good quality ram can be pushed at a certain risk beyond it's rated speed, but the margins for overclocking the RAM itself are usually small.

Dual Channel is a totally different technology, and doesn't affect the speed of any bus, it just effectively doubles the width of the bus, so more traffic can pass without a traffic jam. In other words, dual channel effectively increases "memory bandwidth" enabling the computer to process more data without having to wait for it's turn on the bus.

Imagine a new P4 rig as essentially everything running at 200mhz; The P4 chip itself, the Front Side Bus and the RAM.

Now start multiplying 200mhz by 2 or 4 for the different technologies that increase the apparent speed of the system and you see how much these technologies (DDR, Dual Channel Ram, Hyperthreading, Multiple cpu pipelines) can rapidly increase a PC's performance.

Overclocking is really based on understanding the relationship of the various bus speeds and technologies, and how they all tie in together.

If you want to increase the front side bus from, say 800mhz to 1ghz (1000mhz), you need to increase the actual front side bus speed of 200mhz by 50mhz, to 250mhz. so that when it get multiplied by 2 and then by 2 again, it ends up effectively 1000mhz.

This degree of overclock is RADICAL and turns a 2.4ghz cpu into a 3ghz!

This increase of 50mhz has profound implications for the RAM which is designed to run at a maximum speed of only 200mhz (true speed). It simply will either not work at all or it may damage the RAM module.

One way to fix this problem of the ram being over-cooked, is to reduce the Ram speed by a percentage in BIOS, (if the BIOS supports the option), so that when the Front Side Bus is overclocked, the underclocked RAM then gets multiplied by the percentage increase, and reverts back to it's originally designed operating speed.
This is a simple matter of some basic math.

Another way to overcome the over-cooked ram problem is to buy RAM rated for faster bus speeds, ie. PC3500, where there is no need to reduce the actual ram speed when the FSB is overclocked by a certain percentage. Also, the RAM (PC3500) is truly running at the higher speed, giving some marginal benefit.

Now, we have all this massive power and speed, only to jam it all up on the busses because the road isn't wide enough to fit all the traffic on, This is where Dual Channel Ram Mode comes in, it simply doubles the lanes, (memory bus width) to allow all the traffic to flow un-impeded.

I'm sorry if you already knew all that, but it sounded like it needed clarifying.