Let me elaborate. First though, let's read a wikipedia article on computer fans, shall we?
http://en.wikipedia.org/wiki/Computer_fan
OK, so now you know about some types of fans. Now, onto your MBP's cooler. Inside, there are a set of heatpipes the draw heat off the GPU, CPU, and Northbridge, and carry them to two heatsinks just below the screen. A pair of centrifugal fans are rigged up to suck air in through the keyboard and under the logic board and blow it over the heatsinks to actively cool them. The heatpipes rest against the floor of the case too, making the base of the laptop a passive secondary heatsink (or an active heatsink if you aim a fan at your machine)
Now, these little fans have a rated speed of roughly 6,000RPM. Like most fans, they run at as long as they are fed power. Always. These types of fans can run until their bearings fail, which can takes many years, even if run continuously (see the wikipedia chart on bearing lifespans, remember those ratings are always done at full speed, since the manufacturer can't guaruntee the client will be using it in a device with a PWM controller).
They run off of 5v DC power, I believe, which is what many components in your machine use as well. They receive it through a 4 pin header like the one described in the wiki article (or that's what it looks like, anyways). Well, 6,000RPM is fast. Really fast, even for a small fan like these. Meaning it's NOISY! What to do about that?
Well, if you switch the power on and off REALLY FAST, the result is the same as if you had only half the power. If you vary how many times you turn it off and how many times you turn it on each second, you can vary it's speed from within the program controlling the switch. This is called pulse-width modulation, or PWM for short.
Combine this with the fact that 6,000RPM is an excessive amount of airflow most of the time, well, PWM is employed to slow the fans down to so they are lessy noisy and irritating. Sometimes though, the end user doesn't always agree with the settings chosen for this program, they'd rather punch the fan speeds up a bit. Mac users often use SMCFanControl for this, which is a pretty simple app the raises the base fan speed.
This leads to a paranoia, however: "ZOMG, I BE OVERCLOCKIN MEH FANS!", no, you aren't. You are removing Apple's "underclock", the was put in place to reduce noise and battery drain (no other reason, just that).
Look at it another way: Remember when we didn't have this technology, and our computer fans worked for years anyway? Many desktop case fans still do not use a controller, they simply are connected to the PSU. Yet they last years. Do you think fans suddenly stopped getting less durable now that we have PWM all over the place? No, of course not. Cheap fans just don't die that easily.
So go change your fan speed to what you feel is a good balance or cooling and noise. Have fun.
And since I can hear the "But it broke my fan!!!!" comments already....let's play pretend: Let's imagine that MBP fans are the lowest quality sleeve bearing fans negotiable (which they aren't, they are made by Delta, who is a major manufacturer of these sorts of things) - they would have a lifespan of 30,000-40,000 hours at full speed and the temps you get in an MBP case. Now, let's imagine you bought the original MBP the first day it came out. Now, let's imagine your fans never left that 6,000RPM/high-heat state (maybe you edit video and fold at the same time, and have it fold some more while you sleep). Well, your fans wouldn't have died yet, because the MacBook Pro was only released about 22,000 hours ago.
And considering how over-the-top this was....in a realistic the world, the fan lifespan is probably somewhere around 50,000-60,000 hours, and you probably would sleep the machine at night while you slept.....you get the picture
http://en.wikipedia.org/wiki/Computer_fan
OK, so now you know about some types of fans. Now, onto your MBP's cooler. Inside, there are a set of heatpipes the draw heat off the GPU, CPU, and Northbridge, and carry them to two heatsinks just below the screen. A pair of centrifugal fans are rigged up to suck air in through the keyboard and under the logic board and blow it over the heatsinks to actively cool them. The heatpipes rest against the floor of the case too, making the base of the laptop a passive secondary heatsink (or an active heatsink if you aim a fan at your machine)
Now, these little fans have a rated speed of roughly 6,000RPM. Like most fans, they run at as long as they are fed power. Always. These types of fans can run until their bearings fail, which can takes many years, even if run continuously (see the wikipedia chart on bearing lifespans, remember those ratings are always done at full speed, since the manufacturer can't guaruntee the client will be using it in a device with a PWM controller).
They run off of 5v DC power, I believe, which is what many components in your machine use as well. They receive it through a 4 pin header like the one described in the wiki article (or that's what it looks like, anyways). Well, 6,000RPM is fast. Really fast, even for a small fan like these. Meaning it's NOISY! What to do about that?
Well, if you switch the power on and off REALLY FAST, the result is the same as if you had only half the power. If you vary how many times you turn it off and how many times you turn it on each second, you can vary it's speed from within the program controlling the switch. This is called pulse-width modulation, or PWM for short.
Combine this with the fact that 6,000RPM is an excessive amount of airflow most of the time, well, PWM is employed to slow the fans down to so they are lessy noisy and irritating. Sometimes though, the end user doesn't always agree with the settings chosen for this program, they'd rather punch the fan speeds up a bit. Mac users often use SMCFanControl for this, which is a pretty simple app the raises the base fan speed.
This leads to a paranoia, however: "ZOMG, I BE OVERCLOCKIN MEH FANS!", no, you aren't. You are removing Apple's "underclock", the was put in place to reduce noise and battery drain (no other reason, just that).
Look at it another way: Remember when we didn't have this technology, and our computer fans worked for years anyway? Many desktop case fans still do not use a controller, they simply are connected to the PSU. Yet they last years. Do you think fans suddenly stopped getting less durable now that we have PWM all over the place? No, of course not. Cheap fans just don't die that easily.
So go change your fan speed to what you feel is a good balance or cooling and noise. Have fun.
And since I can hear the "But it broke my fan!!!!" comments already....let's play pretend: Let's imagine that MBP fans are the lowest quality sleeve bearing fans negotiable (which they aren't, they are made by Delta, who is a major manufacturer of these sorts of things) - they would have a lifespan of 30,000-40,000 hours at full speed and the temps you get in an MBP case. Now, let's imagine you bought the original MBP the first day it came out. Now, let's imagine your fans never left that 6,000RPM/high-heat state (maybe you edit video and fold at the same time, and have it fold some more while you sleep). Well, your fans wouldn't have died yet, because the MacBook Pro was only released about 22,000 hours ago.
And considering how over-the-top this was....in a realistic the world, the fan lifespan is probably somewhere around 50,000-60,000 hours, and you probably would sleep the machine at night while you slept.....you get the picture
