I can't tell if that's a serious question or not, but there are too many factors (such as OC'ing, heat, voltage, freak occurrences, etc.) to give you an absolute answer. Nobody truly knows, but my own personal belief is that a CPU that is never OC'd and well maintained will long outlive it's usefulness.
CPU's are almost always the last component to fail in a system. Even OC'd, if you're not stupid with it, a CPU will still outlast everything else in the system. My best guess, assuming no freak occurrences like storm damage or something like that, is 10+ years (well beyond its useful life).
No doubt the CPU is one of the most solid parts of a machine. It sits pinned down usually all nice and cooled and protected it's whole life. Especially the current chips with all the sensors on the die and shutdown before damage features that you get.. it's almost impossible to just kill one unless you do something absurd. Even a bad overclock will just trip the sensor and you reset the cmos and try again. No big deal.
I'd be more worried about HDD/SSD, motherboard, power supply, and even video cards not lasting long enough than the CPU. It's usually the longest living part and when it dies, it's usually because of another piece of hardware killing it (such as the motherboard or PSU), rather than it having a failure of it's own.
Most actually got more than enough life in them to outlast any usefulness. The longest running life of any cpu is closing in on the 40 year mark in the voyager space probes. For a typical home pc and office workstation the typical life is around six years before being tossed out but often kept around yet longer. The oldest running comp that I got at the moment is a old 486 dx2 running at 66 mhz stock.
My list of currently still known-good PCs:
- 14 years old P200-MMX/256MB, about 8 years of 24/7 service behind it and still working last time I put a PSU in it
- 12 years old P3-1066/512MB with about 12 years of 24/7 service behind it, still in 24/7 service
- 12 years old P3-650/512MB with about 8 years of 24/7 service behind it, still using it occasionally
- 8 years old Northwood P4-3000/3GB with about 6 years of 24/7 service behind it, still using it occasionally
- 4 years old C2D-E8400/8GB with 4 years of 24/7 service behind it, still in 24/7 service as my main PC
I have yet to dispose of a motherboard/CPU due to hardware failure, all those I threw a few away (8088, 386SX, 486DX, P100, P200) were simply due to not having any further probable use for them.
So yeah, properly cared for CPUs tend to have much longer lifespans than their performance and expandability is generally considered acceptable for.
I can't tell you how many first gen p4's are still alive in this world.. that's well over 10 years right there.
I still have two Pentium 4's in a Dell and Compaq that run perfectly fine. The reason they've been replaced is because all the other parts mostly the motherboard are too old and obolete now. They have no PCI-e slots no DVI plug limited number of USB 2.0 (only two), all data connections are IDE and lack of other peripherals and features. Other than that the CPU works fine. It's slow and hot compared to the Sandy Bridges but it still works.
The reason they've been replaced is because all the other parts mostly the motherboard are too old and obolete now. They have no PCI-e slots no DVI plug limited number of USB 2.0 (only two) and lack of other peripherals and features.
I wouldn't say my P4 was missing any major features other than support for more than ~3GB RAM and sufficient processing power to decode 720p h264... it had 6x USB2 ports, FireWire, multi-format card reader, the graphics card has dual DVI outputs, SATA and just about everything else needed. The lack of PCIe isn't really a big deal since the P4 would lack the processing power and RAM to run most newer games smoothly anyhow. Motherboards not having DVI back then was perfectly normal since the G-series chipsets had horrible drivers and even worse performance so they were completely worthless for any form of remotely serious gaming and people avoided them like the plague.
Other things that contributed to the P4's quick demise were high power usage with Prescott and horrible IPC throughout the Netburst product line with AMD's Athlon running circles around them... things turned back in Intel's favor with C2D and i3/5/7. Netburst (P4) was a neat concept but Intel's first go at it turned into an embarrassing failure overall - though some concepts still live on in Core2/3/5/7 so Netburst wasn't a complete write-off.
Yes no kidding thats what I'm saying. It lacks all that stuff that computers come with today making it obsolete. The other hardware went obsolete long before the two Pentium 4's which are still working over 10 years later.
A CPU can physically survive for many years. My IBM ThinkPad T40 purchased back in 2003 has a Pentium M 1.5GHz CPU. The laptop still works.
If you are asking how long a quad core CPU will last you before you need to upgrade, then that depends on how much performance you expect from it years later. If all you do is surf the net, do office work, watch videos, then a quad core CPU bought today should still be enough for what you need in 2020.