The P4 Processor Types Thread

Since I've been getting many emails and questions about the different kinds and varieties of Pentium 4's that are out currently and confuse many newcomers and current users of PC's, I figured I'd post this here for everyone to see.  This is my basic description of the current P4's and their differences, and what is relevant to each, and what you should know about them.  I hope this will guide you in your decision if you decide to purchase a Pentium 4 now or in the near future.  Feel free to correct any info if I'm wrong or add some yourselves.

There are many Pentium 4 varieties these days, and I'll break em down as best as possible.  First off:

P4's before the Northwood Core (The Williamette Core) are not relevent to this question, they were shortlived, used Socket 423, and were only 256kb L2 cache and used now outdated RD RAM (which may or may not make a comeback in the future as better and faster XDR Ram)

Northwood Core:  These are the older Pentium 4's on the Socket 478 motherboards, they came in "A", "B", and "C" versions, and all of the Northwood cores were 130nm or .13 Micron .  The "A" version was oldest, it uses a 400Mhz FSB (Front Side Bus) and 512kb of L2 cache.  There is no supported Hyperthreading on these processors, and they use the early versions of slower DDR ram.  The "A" type P4 started at the clockspeed of 2.0Ghz

The "B" version was the same as the "A" version, but with higher clock speeds and a 533Mhz FSB.  The "B" versions usually ranged from 2.4Ghz to 3.06Ghz, the 3.06Ghz model being the first Pentium 4 to use Hyperthreading and the only "B" series model to have it.  They also used slightly faster DDR memory.

The "C" version introduced Hyperthreading Support the the P4, and upgraded the Front Side Bus to 800Mhz.  They ranged from 2.4Ghz to 3.4Ghz, and use the fastest DDR ram available (like DDR400 or 500) and so on.  The Ram on these processors is Dual Channel to give higher bandwidth.

The Pentium 4 Extreme Edition Processors are just Pentium 4's based off a Xeon Processor, they use 512kb L2 Cache and 2Mb of L3 cache, which gives it a big boost.  It uses the 800Mhz and 1066Mhz FSB.

The Newer Prescott cores come in the current "E", "F", "J" and soon to be "P" versions.  They are all 90nm or .09 Mircon (this is the size of the chip, the smaller they get the higher they can be clocked).  The first P4 "E" versions were socket 478 (the older socket now) and didn't perform too well on the then current 865/875 Intel Chipsets.  The Prescott series cores were designed the the 915/925 chipsets.  Something all P4 Prescott cores have in common is that they are now all 1MB L2 cache, which is double what Northwood cores used.  They use 1mb now to cancel out the performance hit of the long pipeline. (the Northwood cores had a shorter pipeline, and the longer a pipeline gets it performs less as good, so they added more cache to soften the performance hit) A shortler Pipeline always gives better performance, although this doesn't mean current P4's won't win in many different situations, it just means processors like the A64 and Pentium M will have the upper hand and perform better in many things.

The Prescotts have a longer pipeline because they now use SSE3 instructions, which in the future will give improved multimedia/game functions for things that take advantage of it (the Northwood cores used SSE and SSE2, Prescott uses SSE, SSE2, and SSE3).  Like Intel is missing 3 instructions from it's EM64T (64-bit) technology which I will get to shortly, AMD is also missing a few instructions from their upcoming A64 versions with SSE3 implementations (Likely these missing instructions wouldn't cause a performance loss when using SSE3).  Precott cores also have slightly improved Hyperthreading, and use the 800Mhz and support up to 1066Mhz FSB, but the 1066FSB doesnt give much performance difference at all.

Shortly after it's release, the Precott P4's switched from socket 478 to the now current Socket LGA 775 also known as Socket T.  These current P4's use the Intel 915/925 type chipsets, which they were built for.  These new chipsets also use a newer, better memory controller, have Intel Matrix Storage Technology (For RAID), and use Dual Channel DDR2, which in future will be much faster and better than what it is now because it's still a newer and early technology.  These chipsets also brought about the first implementations of the technology PCI Express.  PCI Express (PCIe) is the new standard that replaces AGP and in the future standard PCI technology as well.

When Intel released these new P4's on the LGA 775 socket, they changed the way they named their Processors.  They now rate them in a number scheme rather than in Ghz.  Examples are given below:

The "E" series processor uses like the rest of the P4 prescott cores 1Mb L2 Cache, 800Mhz FSB, Hyperthreading, and on the current LGA 775 versions DDR2 ram.  They come in the P4 520 (2.8Ghz), P4 530(3.0Ghz), P4 540(3.2Ghz), P4 550(3.4Ghz), P4 560(3.6Ghz), and P4 570(3.8Ghz) versions.  The "E" version processors, since they are the earlier type, tend to have some heating problems sometimes, though not with every kind.

The "F" series P4 is the same as the "E" series, but better revised core for slightly cooler running, and now enabled EM64T technology. (The same as AMD's A64 technology but with 3 missing instructions, and again likely that these missing instructions wouldn't cause a performance loss when using 64-bit, just like with AMD's SSE3 implementation.  The reason for the missing instructions is because Intel couldn't get them to work, AMD couldn't get the same 3 to work in the beginning either, but they eventually solved and fixed the problem) EM64T enables the processor to run in faster 64-bit mode in future when Windows XP 64-bit is released or in the future Microsoft's new OS codenamed "Longhorn".  Otherwise the chip still runs in 32-bit mode like every other until it can be used otherwise, EM64T is a good feature to be sure to have.  The "F" series processor also uses EDB (Execute Disable Bit) technology, which protects against some virus attacks trying to create a buffer overrun on your system.  The "F" series isn't widely available as of now, and it doesn't look to be anytime soon.

The "J" series P4 is the same the the above except it doesn't have EM64T, it only has better revised core to run a bit cooler and the EDB technology.

The "P" series P4 is the best of the batch, it uses the technologies listed above along with EIST (Enhanced Intel Speedstep Technology) to downclock the processor when it isn't being used to save energy, run cooler, and give it a longer lifetime.  This processor will be widely available in the future I believe.

That is the basic rundown of the P4 series processors.  In the near future there will be a "6xx" series P4 that will all use the above listed technologies and include 2mb of L2 cache, and the later on "8xx" series P4, which will be the first dual core processors from Intel, but will require a future chipset. 

Enjoy