| |
 |
CD Recording FAQ
12. Troubleshooting
12.6. Overclocking and cd recording
Overclocking was always an attractive option, especially since continual progress in microelectronics turns a CPU into an often overpaid short-term investment. Especially since the Celeron 300, overclocking became a natural option and actually there is little reason not to at least try it. However, a risky by nature process as that of cd recording needs a steady system to rely upon, especially concerning the performance and stability of the storage devices, a point often by ambitious overclockers.
So, there must be a limit between performance and stability, and this is vital for a machine performing cd recording tasks, since data are always more valuable than a faster CPU.
12.6.1. Overclocking basics
Overclocking is done by changing the multiplier and/or the system bus
frequency. Since all Intel made CPUs are multiplier locked, the FSB is
the only thing remaining for tweaking.
The PCI bus runs at 33MHz. This speed is related to FSB via a divider,
(1/2, 1/3, 1/4). For FSB=66MHz, the divider is 1/2, so PCI bus speed is
33MHz. When we move up to 75MHz, the PCI bus speed becomes 37,5MHz. Finally,
when we go up to 83MHz, the PCI bus speed reaches the dangerous value
of 41,5MHz. At 100MHz, the divider becomes 1/3, so the PCI bus speed is
normal again. As we move from 100MHz upwords, the same pattern is repeated,
till we reach 133Mh, where the divider becomes 1/4. A similar divider
exists for the AGP slot.
These settings vary depending on the motherboard, so you have to check your motherboard manual before trying anything. Modern motherboards offer a wider range of FSB values, allowing you to change FSB at intervals of 1 or 2 MHz and adjusting the PCI bus speed properly. For example, at 90MHz the divider can be 1/3, thus downgrading the PCI bus speed at a safe 30Mhz.
When the PCI bus speed is raised, PCI cards and peripherals attached to them have to work harder. The official PCI specifications are at 33Mhz, so going beyond that limit is a risk. Cards begin to overheat and even fail to work, while the same happens with hard disks. Recorders, on the other hand, are not as much affected, because recording is a process of a strictly fixed speed.
The 37,5 PCI bus speed is the most interesting case, since it corresponds to 75FSB. Though not in compliance with the strict PCI specifications, 75FSB is the official FSB for Cyrix CPUs, so most peripherals have been tested to work at this speed. Not only that, but the increase in PCI speed brings an equivalent increase in hard disk speed, provided that the hard disk can cope with that.
Few PCI cards and modern hard disks have trouble at 75FSB, but things are different at 83FSB, since 41,5 PCI bus speed is far beyond the official specifications. The result is overheat and a lot of NIC cards and SoundBlasters will have trouble.
The most dangerous implications have to do with the hard disks. Running a hard disk out of specs can easily destroy its FAT and data and the only solution will be repartitioning/reformating.
This does not mean that 83FSB is impossible. With proper cooling and good choice of peripherals, 83FSB can be achieved, however it is best to be avoided.
Before you boot from the hard disk at such a speed, try booting from a floppy instead, and then try formatting a floppy. If the procedure completes without errors, then you have chances to be safe, provided that you already have a backup of your hard disk.
12.6.2. How overclocking affects cd recording
Overclocking affects cd recording in 3 respects: General system stability, case temperature, and storage subsystem stability and reliability.
Even if an overclocked system seems to work fine, this does not mean that it is able to maintaining its stable operation.
Your system may manage to get through POST and enter Windows, but this is far from enough. Occasional lock ups, BSODs and error messages mean that for some reasons stability cannot be maintained.
A tough test for any system is to compile a Linux kernel. If you do that 3 times and succeed all of them, then you can be almost certain that you can stress your computer without stability problems.
Another good test is zipping and then extracting a large number of files.
If you get CRC errors, then definitely something is wrong, especially
for a cdr system. An even more reliable test is running CPU
Stability Test. You can leave it running overnight, and if till next
morning your PC hasn't crashed, then you have an indication that you can
trust your overclocked system..
Something else to note is that operation under Windows is one thing and
operation under Linux or BeOS another. If your PC runs stable under Windows,
that doesn't mean that it will be stable under Linux.
A common result of overclocking is that more heat is generated by the processor, shortening its life time and affecting all nearby cards and peripherals, which can also radiate heat as a result of overclocking.
First of all, a good, large heatsink and cooler have to be attached on the CPU. Applying a thin layer of thermal paste between heatsink and cooler is almost necessary, while there are always the solutions of an Alpha cooler or a peltier (though far more expensive and harder to find).
However, even more important is keeping the case temperature low. Heat affects the quality of written cds, can be the reason for coasters, and has a negative influence upon a recorder's life expectancy and reliability. Add this to the fact that many drives overheat because of bad design, and you can see how important keeping case temperature low can be.
The first step is to buy a case with many free positions for extra coolers (since it is very difficult to find one with those coolers already installed in factory). Usually you will need 8cm, 12V coolers, easily found at Radio Shack, plus some Molex plugs and power splitters so you can plug them on the main power supply (usually you can plug 4 of them without having to worry about the power supply). However, you may need smaller coolers too, depending on the case design.
When placing the coolers in the case, you also have to think about the air flow. Air must enter the case from one direction and leave it from another, so you have to plan carefully, especially since you need to cool the entire case and not just the CPU.
The cooler which rests inside an ATX power supply sucks air into the
case (which means that actually raises the overall case temperature),
so reversing it can be a good idea. All you have to do is turn it the
other side, but the power supply is a very dangerous kit, so don't do
that unless you really know what you are doing or you may get electrocuted.
Another point of interest is the use of "software coolers".
These are programs which will implement the HLT command in Windows, putting
the CPU into sleep when idle. The problem is that these programs will
offer nothing when your system is under load, when playing games or running
processor intensive tasks. Though cd recording by itself rarely uses more
than 5% of the CPU of a modern PC, recording programs become more and
more complex, especially when dealing with audio (mp3 encoding/decoding,
filters etc). The point is that your system should be stable even without
the use of such programs.
Ooverclocking often demands to raise the CPU voltage, which is dangerous for the CPU itself and increases the heat generated by it. A 10-15% increase is not extravagant, but going higher than that can be a source of problems. The opposite, decreasing CPU voltage in order to get it cooler, can prove to be a bad practice, since the CPU needs a certain voltage in order to operate without accumulating errors, while decreasing the voltage increases current.
Changing the PCI bus frequency is beneficial for the overall system speed, since it makes the PCI cards and the hard disks run faster, provided that you don't pass the line and cause damage to them. Balancing these two factors can be a real dillema, where stability has to come first. There is no doubt that CPUs and peripherals have margins to go faster, but you cannot avoid the fact that when a circuit runs out of its specifications, errors occur and accumulate. These errors are not perceived by the user till the point their accumulation causes malfunction.
There is the opposite side as well. Suppose you choose 90FSB, with a
divider of 1/3, which means an underclocked PCI bus running at 30MHz.
Let's make a comparison for a Celeron 400 (66FSB, multiplier=6):
At 75FSB, Cel400 goes at 450, running at 37,5 PCI bus speed.
At 90FSB, Cel400 goes at 540, running at 30PCI bus speed.
As you can see, what is gained in CPU speed is lost in PCI bust speed.
Running the CPU at 540 is not sure to be safe for system stability, so
you have to choose between CPU and PCI bus.
37,5 PCI bus speed is the best compromise. Almost all cards and hard disks can cope with that, while the system speed is increased uniformily, so if you can't go to 33, it is better to compromise with 37,5 instead of going to 41,5.
Always remember that data written on a cd may get corrupted if running
your system out of specifications. 37,5 PCI bus speed is not completely
outside the margins, but anything beyond that definitely is.
If your data and your work are really important, it is better not to risk
overclocking. However, you can overclock and still have a reliable system,
provided that all precautions are taken.