Atomic I/O letters column #6
Originally published in Atomic: Maximum Power Computing Reprinted here 27-Apr-2002.Last modified 16-Jan-2015.
PSU puzzle
A 550 watt (!) Enermax EG651P-VE PSU, as reviewed here.
Enermax: The Choice Of Loonies.I read with interest Atomic's recent article on power supplies. I recently built a new machine with a 1.2 Gig Athlon CPU and "to be on the safe side" bought a case that boasted a 300W power supply. Exactly a month later it failed, and I was back to the search for good information on the subject. Basically there are two questions that we would all like to know the answer to:
a) How do I calculate much power I really need for a given system, and
b) How do I know if the power supplies on sale are any better or worse than each other?
Chris Caudwell
Answer:
Power supplies do not have just one output. Sure, if you take the amp ratings for the +3.3, +5 and +12V "rails" and multiply them by the voltages and add them all up then you'll get a number, which may resemble the power rating on the sticker. But your computer is unlikely to load each of the PSU's rails evenly.
If you've got a "300W" PSU with 3.3, 5 and 12 volt rail ratings of 20, 30 and 12 amps respectively, then just multiplying and adding gives you 360 watts. But that's split up among the rails into 66, 150 and 144 watts, respectively, and one rail can't "lend" power to another.
Moreover, if you max out one rail - if you've got a bunch of devices sucking on the 5V rail, or a fan-farm drawing power from 12V - then the voltages on the other rails are likely to sag in sympathy, and flake out your computer.
And, of course, dodgy PSUs such as come with many cheap cases may have a short lifespan, no matter how lightly you load them.
The overall wattage rating on the sticker doesn't give you much idea of the capabilities of the PSU, by itself. There are lots of cheap yum cha PSUs with optimistic ratings. Even the individual rail current ratings can be misleading; they may, for instance, be rated according to the maximum power they can deliver at the rated voltage when the other rails aren't loaded at all. Which is, of course, not realistic.
It's generally a decent rule of thumb that if you work out the wattages for all of the rails, add them together and end up with a result substantially higher than the overall power rating, then you're probably looking at a decent PSU. If the rail powers added together don't equal the overall power rating, then you're definitely looking at a lousy one.
Anonymous Asus
I've got an Asus A7V-VM mainboard. I just want to ask you what graphic chip is it using? Does this board support the AMD Athlon 1.33GHz C-type CPUs and let them run at full speed?
Richard Liu
Answer:
It's hard to pin down information about this board, but I presume you've got an HP Pavilion PC. I presume this because I'm pretty sure that Pavilions are the only machines that ever contained the VM variant of Asus' popular A7V. Asus have made special motherboards for a variety of HP machines.
If you've got a VM with built in video - not a separate video card - then it ought to be using the Via KM133 chipset, which is based on the KT133 - not the newer KT133A. That difference matters.
The video adapter on KM133 boards is an S3 ProSavage, which is very slow for 3D, by current standards. Not useless, but not even slightly exciting, even if you only compare it with a modest graphics card like the old TNT2 Model 64 ("M64"). One of those will spank a ProSavage.
Despite the "133" in its name, the KM133 chipset can only do 100MHz Front Side Bus (FSB). The updated KT133A can do 133MHz, but the KT133 and its relatives can't.
Thanks to the Athlon's clock-doubled bus design, 100MHz FSB means a 200MHz processor-to-chipset bus speed. Athlons that want a 133MHz bus speed will work on a 100MHz-only board, but they'll run at 3/4 speed. So a 1.33GHz Athlon will give you only 1GHz.
BIOS blasting
When resetting the CMOS/BIOS password through changing the BIOS password jumpers to the clear position, is it necessary to place the jumper in the clear position, boot up the computer, shut it down, replace the jumper to the original position and boot up again, or is it possible to set the jumper to the clear position, then back to the normal position without starting, and boot up?
Joel Little
Answer:
The Clear CMOS jumper that's present on many motherboards removes backup power from the memory chip that holds your computer's BIOS settings. The backup power's provided by the battery on the motherboard - usually a lithium coin cell, these days - when the computer isn't getting mains power.
Modern ATX machines generally use the five volt standby line from the power supply to maintain the CMOS memory when the computer is plugged into the wall, but isn't turned on. For the Clear CMOS jumper to work, you therefore have to disconnect the power lead first.
The jumper isn't just for clearing a BIOS password, if you've set one; it clears all of the CMOS settings back to the defaults. And no, you don't need to turn the computer on for the clearing to work. Just unplug the PC, set the jumper to the clear position for several seconds, set it back to the original position, and power up again. That's all there is to it.
Some motherboards have a couple of solder pads rather than a proper jumper. To clear the CMOS on one of them, you have to short the pads for a few seconds with a screwdriver, coin, broadsword or platinum ingot. Cadillacs work, too, but you'll need a long pointy one that'll fit inside your computer case.
Quake quickie
Hi! You'll probably laugh at me for not knowing this but how do I use the quake 3 timedemo for benchmarking? Is the Quake 3 benchmarking program that you use available to the public? If so where do I get it from and how do I use it?
Ben
Answer:
You can do timedemos from the Q3 console easily enough, but there's a utility called Q3Bench that makes repeated test runs far simpler. You can get it, and its documentation, from here.
Upgrade questions
Hi! I want to buy a new computer and would be grateful if you could answer a few questions.
1. Would 128Mb of DDR RAM or 256Mb of SDR memory be better? If 128Mb is adequate for a gamer who won't be able to upgrade for a long time (a few years) should I go for DDR?
2. How could I improve my really old 133MHz Pentium with 16Mb of RAM for fairly cheap to use as a spare computer/word processor?
Shadow Spear
Answer:
1. Double Data Rate (DDR) RAM does give Socket A (Athlon and Duron) systems better performance than the same amount of Standard Data Rate (SDR) RAM, but not by a big enough margin to justify much of a price premium. When I originally wrote this reply for Atomic magazine, US pricing for quality DDR and SDR RAM was pretty much the same, making DDR a better buy if your motherboard could handle it, but Australian pricing for DDR was still silly. Now Aussie prices have caught up, and DDR is obviously superior.
128Mb of RAM is enough for a Win95-series-OS game machine, including WinME boxes, but it doesn't hurt to have a bit more. The cheapness of RAM these days means 256Mb is an easy enough purchase; 512Mb will satisfy Win2000 and WinXP power users. This doesn't mean that many people don't buy a lot more RAM than that, mind you, but there's really no need for it if you're not doing very RAM-intensive tasks, like super-high-resolution Photoshop work.
2. Upgrading old Socket 7 machines like your Pentium isn't a very economically sensible thing to do. SIMM RAM modules to suit them are much more expensive per megabyte than current-model DIMMs, and you can't use the faster Socket 7 CPUs, because the old motherboards don't support high enough Front Side Bus (FSB) speeds. The motherboard may work with, say, a 500MHz K6-2, but it'd only run it at 333MHz. Which would still be a large improvement, mind you.
Faster, Fifi! Faster!
I have a Celeron 566 running on a SystemBoard M754LMR Socket 370 motherboard. My problem is that when I try overclocking by changing the CPU multiplier settings either directly from the motherboard or in the BIOS it makes no change at all to the speed of my CPU. How can I overclock my CPU on my motherboard? Thanks for any help.
Danny Weaver-Koenigs
Answer:
All Intel CPUs for some time now have had a locked multiplier. It doesn't matter what multiplier you ask for; you get the one the CPU uses as standard.
To overclock, you have to increase the Front Side Bus (FSB) speed, and possibly also the CPU core voltage, if your processor can't quite manage a given FSB at stock voltage. Your little three-slot integrated-video PC Chips motherboard (Awww! Ain't it cute!) supports only 66, 100, 105 and 133MHz FSBs, and has no voltage adjust feature, so you're probably out of luck.
"Systemboard", by the way, is just a brand name that PC Chips use for their motherboards, along with their real name. PC Chips is not what you'd call an illustrious marque in the overclocking scene.
Your Celeron runs at 66MHz FSB normally. If you set your motherboard to 100MHz FSB, that corresponds to an 850MHz core speed. A C-566 may actually be able to handle that, because it's the second-lowest-clocked Celeron to use the P-III based "Coppermine 128" core, not the old P-II based one. Those older Celerons topped out not far above 500MHz.
850MHz is certainly not unheard of for C-566 CPUs; 800MHz capability's common enough, and some manage 900MHz. You're likely to need to boost the core voltage, though, and the M754LMR doesn't let you do that.
The Laptop Of Mystery
I have bought a second-hand laptop and it kept crashing, so I formatted the drive and installed WinME. But unfortunately I belatedly realised that I did not have the recovery disk for the video drivers etc. Could you please tell me how to find out what drivers are needed, as the people that originally sold the laptop are not helping at all.
The laptop is a "Highlander", model HL63A, the processor is a P3 600MHz and there's 256Mb of RAM. Please help as this laptop is for school and I really need to get it working.
ds98 Stocker
Answer:
Well, Mr Stocker, I don't know what hardware your laptop's using.
What I do know, or am at least sure enough of that I let it be printed in a magazine, is that "Highlander" laptops are actually a Clevo product.
Clevo do a roaring trade in cheap laptops, which are so cheap because they use some desktop-PC components, like CPUs, instead of the special lower power consumption laptop ones. So some corners are cut, but you get a good general feature set for the price.
If you go to the Clevo site and look up whichever Clevo-brand product matches the specifications of your laptop, you'll be able to download the driver package for that machine and you should be OK.
Optimal, schmoptimal
I have been told that each processor has an "optimal" amount of RAM. Can you please elaborate on this topic and tell me what my optimal amount of RAM is (I have an AMD Duron 800MHz with 128Mb at the moment).
Thomas Baxter
Answer:
You know, I've been told that squirting coffee up your bottom can cure cancer.
This belief, and the belief that the amount of memory your computer should have has something to do with the CPU it uses, are both based on no sound evidence.
Your computer needs enough memory for all of the stuff you want to do at once. Modern operating systems, including all of the Windows flavours, use hard disk space as "virtual memory" when they run out of real, or "physical" RAM. The hard drive's much slower than real RAM, so if you want decent performance from a PC, you need as much physical RAM as is necessary for the tasks you want to perform.
Generally speaking, that means 128Mb for the average game-playing Win95, 98 or ME user. Another 64 or 128Mb will help a bit more, but nothing to get excited about. Given how very cheap RAM is these days, though, why not?
If you're using an NT-series OS, including Windows 2000 and XP, then you want 256Mb, or at least 192Mb. If you're doing very memory intensive things - heavy multitasking, graphic design, database serving, CAD, scientific computation - then you may need a lot more.
But the speed of your CPU's got nothing to do with it, except insofar as an old slow CPU isn't going to give you half-decent performance for various tasks including current games, no matter how much RAM you've got.
Invisible FSB
I finally got around to overclocking my Intel 815e, and then I realised I can't figure out how to change the CPU's FSB, let alone the multiplier (which you already said couldn't be changed). I have currently got a PIII 733MHz and I've looked and looked for a FSB setting that could be changed in BIOS; is it just me or is my CPU not overclockable by standard means? Is there a way to get around this?
David Greenfield
Answer:
Not all motherboards have FSB adjustment. Intel-CPU boards that aren't made for overclocking commonly just look at the CPU's FSB ID pins, which let the motherboard know what FSB the CPU wants in order to run at stock speed. The motherboard locks the FSB to whatever's indicated by the FSB ID pins, and that's it. You can't change the FSB on such a motherboard without some quite adventurous hardware hacking.
