First I will say if you want this answer to determine which processors you should buy, look at benchmarks instead. They will give you a much more reliable comparison between processors.
I'm also assuming you are only concerned with the differences between Intel and AMD processors. There are other brands that design processors for non-desktop computers (gaming consoles, mobile phones, etc), and outlining the differences between all of these would probably make any sane person crack.
Having said that, here's some differences:
Differences you will see on the box:
- Amount of cores (i3 usually has 2 cores, i7 will usually have 4)
- Clock Speed
- Overclocking ability
- Cache size (L1, L2, and L3 cache sizes)
- Fabrication size (refers to the separation between memory cells. IE
- Power dissipation (generally correlated to the fabrication size)
- Quality of on-board graphics (though, not all processors even have this)
- Support for hyper-threading
Differences you won't see on the box:
- Bus sizes
- Dhrystone instructions per second
- FLOPS (floating point instructions per second)
Differences uncommonly found:
- Support for branch prediction (most Intel processors have this, I think)
- Maximum memory (3rd generation Intel Processors maxed out at
32GB, I believe the 4th goes up to
There are many other differences I could mention, but these are most relevant to end-users. If you are a programmer, for example, the different abilities of the processor's instruction set may make a big difference to you. If you are a system administration, you're probably more focused on server processors (commonly Xeon processors).
i7s are not subject to higher controls in the way that you think they are. This is how the different
i7s generally come about:
- A Single CPU is designed, fabricated, etc.
- Batches of the CPU are run through intense performance tests (How many cores are correctly running? What's the max clock frequency? How much power does it dissipate? etc)
- Features of each processor are disabled or limited based on the test results
- The processors are then divided and labeled accordingly
This process is called binning and is common many different manufactures and products of the solid state type. Therefore, i3s aren't designed differently than i7s. In fact, it's the same design, just different fabrication results (the fabrication process isn't perfect).
As DavidSchwartz pointed out - if a company needs more of a certain lesser processor (ie more
i3s of a line of processors), they will physically disable some features (even if they pasted the test results) of a better batch to make it equivalent to the lesser module.
Making a rough comparison (Intel):
- Check the cache sizes (L1, L2, and L3)
- Can it overclock? How much?
- How many cores?
- How much power does it consume?
- How much ram does it support (also depends on the motherboard)
- Does it have on-board graphics?
- What generation processor is this? (right now, Intel has four. A new one every ~ year).
- Does it support hyper-threading?