Nowadays the basic way to identify Intel processors (Pentium 4 and Celeron) is through their clocks. The greatest problem that Intel faces is that many times same-clock processors have different features. To get rid of this fix, Intel usually adds a letter after the processor clock to differentiate this extra feature.
For instance, nowadays there are two 3.2 GHz Pentium 4 models on the market, one has 8 KB of L1 cache memory and 512 KB of L2 cache memory, and the other has 16 KB L1 cache memory and 1 MB L2 cache memory. The model with more cache memory uses a letter E (3.2 GHz E) so it can be differentiated from the model with less cache memory.
Another example that shows well this problem is found in the 2.8 GHz Pentium 4 processor: there are four models of this processor on the market, all of them having different features. The original model, the model using Hyper-Threading technology (a resource that enhances the performance of the processor), which is identified by the letter C, the model with more cache memory (16 KB L1 and 1 MB L2) and Hyper-Threading technology, which is identified by the letter E, and the model with more cache memory that does not use Hyper-Threading technology and has a 533 MHz external bus (the other models have an 800 MHz external bus).
If professionals from the area are confused with the adoption of those letters, imagine you!
The solution Intel will start adopting from May or June is to use a single number for each processor, in other words, a model number, as it happens with printers and digital cameras. It is the same idea that AMD has been using in their Opteron processors. This model number will indicate only the processor features and will be useful for the comparison of processors from the same family. In today's standard, it is possible to differentiate same clock models using the letter, but there is no way to know, beforehand, which model is better or faster. In this new system, the rule is simple: the higher the model number, the more resources the processor has, which generally means better performance.
The numbering standard will consist of three numbers, the first one indicating the processor family: 7 for Pentium 4 Extreme Edition (or Pentium M, in notebook processors), 5 for Pentium 4 and 3 for Celeron. The two other numbers compute all the processor features, such as internal clock, external clock, cache memory size, and technologies, such as Hyper-Threading, SSE3, etc.
For the example given (2.8 GHz Pentium 4), it would have four different model numbers, one for each model, instead of just being classified as 2.8 GHz Pentium 4 and optionally having a letter that, as we saw, is difficult to understand.
For instance, the 3.6 GHz Pentium 4 will be called Pentium 4 560 and the 3.4 GHz Pentium 4 will be called Pentium 4 550. As you can see, the 560 is better than the 550 because of its having a better clock.
The only drawback is that, except for the first number, the others don't have any special meaning, that is, there is no correlation like every processor ending in zero has 1 MB L2 cache and 800 MHz external bus. To know the technical features of a certain model number, you will have to visit Intel's site to decode its meaning.