how a CPU operates when looking at fundamental operation of CMOS requires and understanding that CMOS slew rates cause heat dissipation and rising temperatures reduce the slew rates thus increases slew rate even more and propagation time increases as well. If there is a set margin in timing before a race condition then it can be said with constant clock speed that the MPU may run slower rise times and increased clock delays so the margin before lockup due to a race condition in the chip or external memory may cause failure.
This explains why MPU's that run hot will work after a cool down period.
Apparent aging of CMOS gates can occur if moist dust accumulates on the exposed bus soldered lands. This can add many pF of loading which can reduce the rise time of bus signals and increase the internal heat dissipation causing further reduction in slew rates.
Another cause of apparent aging is the increased number of background tasks installed by the user startups and resulting in excess heat during so called idle activity. trimming the startups can reduce the overall CPU load and thus restore normal temperature rise due to excess processes running. For example XP on clean install of a retail version might have 25 processes running and an OEM version with many user auto-installed services and startup processes in the registry, might increase this number of processes as shown in the TaskManager process Tab to say 50, and even up to 100 from my experience of inexperienced users. DIsabling these processes using simple programs such as MSConfig can help, but WinPatrol is even better and free and restore cool operation as a new.
As pointed out by others, there are internal failure mechanisms which also slow down the slew rates of gates called time-dependent dielectric breakdown from ElectroMigration growth on the semi-conductor material. This is dependant on stress levels of heat and voltage and also exposure to gamma radiation in space.
All of these factors contribute to why the temperature rise and loss of time margin occurs in laptops from aging, even after a fresh install of OEM image. So 5yr old latops will run hotter which means they must have longer slew rates and thus elevated temperature rise above ambient and that means it must be running slower rise times. But the clock rate is fixed so the performance if working will be the same until the margin drops to zero without warning. So monitor your temperature rise and do not exceed 70'C for reliable operation is my best advice. 60'C is preferred maximum where most CPU fans start to run at full speed.
There are many reasons why CPU's get hotter with aging.
One reason requires and understanding of complementary switching. Simply put, it is a synchronous pull up switch that turns on while pull-down shuts off. During the interim there is a momentary short circuit if there is a crossover from unequal slew rates or switching times. New technology of CMOS may compensate for this characteristic that is temperature & voltage dependant to introduce faster switching times but with a controlled dead time to eliminate transient power loss during crossover. Although ElectroMigration is one reason of additional delays, it is not obvious if this is symmetrical.
Never-the-less CPU temperature rise is a widespread phenomena with aging {with laptops sensed by users lap of gradually getting hotter over the years} and this helps to explain the reasons. i.e. aging cause gradual slew rate increase which affects dynamic power consumption of a steady clock frequency or a repetition rate of cross-over transitions. Since we know the steady state leakage power is negligible, it is this effective driving force of complementary outputs with momentary current surge that drives CPU temperatures up. So CPU idle temperature is a strong indicator of aging or slowing down of slew rates if everything else is constant.. (CPU load, V+, ambient temp, cooling efficiency, dust elimination) YOur CPU will still execute instructions at the same speed but run hotter and thus with less timing margin before a race condition occurs. ( read data when not ready due to propagation delay)
The same phenomena exists in desktop CPU's but users may not be aware of gradual increase in fan speed over the years that compensates for increased heat dissipation from gradual aging. There is no empirical study to my knowledge, but it is my personal observations of CPU's over the last 20 years that this happens in many cases, but not all.
Related: Do computers slow down as they age?
– kenorb – 2016-07-23T15:02:44.3878I suppose that in theory, a CPU could run slower as it ages if the cooling mechanism doesn't cool as efficiently as it used to (maybe the fan breaks a little and can't reach top speed), I think some CPUs can automatically scale back their clock speed if they detect they are too hot. Note that this doesn't mean the CPU itself is aging into poor performance; in this scenario, replacing a bad fan would probably allow the CPU to run as fast as when it was new. I don't have any references to back this up though, but it seems plausible to me... – FrustratedWithFormsDesigner – 2012-08-01T20:47:58.493
3@FrustratedWithFormsDesigner, I've seen a Dell notebook throttle its CPU severely because it thought it was getting too hot (mainly through bad design I believe). It's entirely feasible that the build up of dust over time can cause that too, but you're correct that it's not strictly age that causes it. – Highly Irregular – 2012-08-01T21:55:41.463
34What gets slower is the software. – Daniel R Hicks – 2012-08-01T22:00:13.393
See - http://superuser.com/questions/55218/why-does-hardware-get-slower-with-time/55226#55226
– ChrisF – 2012-08-01T22:22:50.77718
Here is a great IEEE article written specifically in regards to transistor aging I urge anyone interested in this topic to read.
– Breakthrough – 2012-08-01T23:50:24.207@ChrisF The first bullet point in your link is about one's perception of hardware. I was hoping more for a answer based on objective, repeatable benchmark data. In the same question, I did find this answer enlightening: http://superuser.com/a/55316/149691
– Ben Simpson – 2012-08-02T00:04:55.463@Breakthrough Fascinating article. It looks like there are three phenomenon which cause CPUs to degrade in performance over time 1) hot-carrier injection, 2) hot-carrier injection and 3) oxide breakdown. The first two cause gradual slowdown, however the third is a catastrophic failure. – Ben Simpson – 2012-08-02T00:15:51.177
1Bah - just noticed that #2 should read bias temperature instability – Ben Simpson – 2012-08-02T00:25:24.803
1@Breakthrough If I understood correctly CPUs do get worn out (and slow down) but the effects can only be perceived after many (10?) years. How is it that so many answers specifically say "NO"? Wouldn't a more accurate response be "Not in the first year" or something like that? – João Portela – 2012-08-02T09:20:02.197
@BenSimpson - I meant to link to the question :) While there may be a real effect in the hardware it's swamped by your perceptions and the fact you run more/bigger programs. – ChrisF – 2012-08-02T09:51:48.013
If yes, Will there be a significant change in clockspeed? – Khaleel – 2012-08-02T12:33:43.690
2@JoãoPortela it's all relative. The CPU will run at the same speed/voltage until some transistors stop functioning correctly due to age. The only way to solve the problem at that point is to either slow the CPU down by reducing the clock speed, or increase the operating voltage (further aging the transistors on the CPU die). And of course, over time, the clock generation units in the CPU also become unstable, leading to more clock jitter. – Breakthrough – 2012-08-02T15:18:43.937
@QuickSilver it's a synchronous circuit, and you tell the CPU how fast to go. The issue is that, over time, the CPU needs to be run slower and slower as the transistors age. They take longer and longer to switch, and when this switching time becomes too long, the computer will crash (the same when you overclock a CPU too much). See my previous comment as well. – Breakthrough – 2012-08-02T15:20:02.733
Note, there is a difference between actual speed and perceived speed. – Thorbjørn Ravn Andersen – 2012-08-02T19:10:39.940
Reminds me of: http://superuser.com/questions/375160/
– Freesnöw – 2012-08-03T02:00:48.880