Why aren't all CPUs 'overclocked' as a factory default? [duplicate]

First of all, not all CPUs are capable of overclocking. Many have fixed or range-limited multipliers. This is intended by the industry, hardware vendors are happy to sell CPUs and peripheral hardware with more freedom for higher prices. Real 'overclockers' seem to pay anything as long as it enables them to double the factory defaults ...

Secondly it's a cooling and efficiency problem. Energy consumption and frequency don't scale linearly, nor does the actual performance (especially considering that, with faster CPUs, other system components quickly become bottlenecks ...).

With overclocked CPUs, there is also a strong variance in durability and lifetime even within a manufacturing series. The frequency at which they're sold is a frequency at which all units of a series are known to work stable, regardless of possible differences in detail. One CPU of a series may fail quickly as you overclock it while another may work stable up to 4+ Ghz.

CPU Binning is relevant here:

http://en.wikipedia.org/wiki/Product_binning

Semiconductor manufacturing is an imprecise process, with some estimates as low as 30% for yields. Defects in manufacturing are not always fatal, however. In many cases, it is possible to salvage a part by trading off performance characteristics, such as by reducing its clock frequency or by disabling non-critical parts that are defective. Rather than simply discarding these products, their performance level can be marked down accordingly and sold at a lower price, fulfilling the needs of lower-end market segments.

This practice occurs throughout the semiconductor industry, including central processing units, computer memory, and graphics processors as well.

As well as the tolerances and MTBF reasons posted, there is another one as well.

(Please bear with me as I have not kept up with hardware for a very long time.)

The cost for intel to make a fabrication plant that can create a specific chip is a very large fixed cost. The cost for them to make a single processor once they have built the plant is very, very small.

There is an economic advantage of making the same die for a series of chips, and then locking the chips at different multipliers for product differentiation and pricing. This way, the chips all come out of the same plant. Instead of having a unique plant for each single speed of chip. If you want to buy a low-end chip, the economic way for intel to do it for you is often to sell you a mid-end chip which is set up to run at a lower frequency.

You will see this in other markets as well, when the manufacturing process requires a high initial fixed cost and a very low marginal cost. Every major brand aluminum bicycle, for example, is actually made in the same factory, by the same robots.