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arithmetic logic units and they operate at twice the speed of the processor. While this might sound like absolute heaven, it is good to keep in mind that they had to do it this way due to the pipeline design in order to even keep integer performance up to that of the Pentium III. So, this is really a necessary design change due to the increase pipeline size.• Execution Trace Cache
Intel also did some re-working of the P4's internal cache in order to nullify the effects of a mistake in branch prediction that can be a real lag with a 20-stage pipeline. First, they increase the branch target buffer size to eight times that of the Pentium III. This cache is the area from which the branch predictor gets its data. Secondly, Intel reduced the size of the L1 data cache to only 8K in order to reduce the latency of the cache. This, no doubt, increases the need for the 256 KB on-die L2 cache, and the latency of that has been improved on the P4 as well. Lastly, Intel added a execution trace cache. This is a new cache that can hold instructions that are already decoded and ready for execution. This means that the processor
The early Pentium 4's made use of the Socket 423 interface. One of the reasons for the new interface is the addition of heatsink retention mechanisms to either side of the socket. This is a move to help owners avoid the dreaded mistake of crushing the CPU core by tightening the heatsink down on it too tightly. The retention bases hold the heat sink onto the CPU. Socket 423 was short-lived, and Pentium IV quickly moved to Socket 478 with the release of the 1.9 GHz. Also, P4 was, at its launch, associated exclusively with Rambus RDRAM. Intel was stuck in this agreement with Rambus, and this was an obvious hurdle for promotion, being that most computer users to not have Rambus and don't wish to buy any. So, early retail P4's actually came packaged with two 64MB sticks of RDRAM. With chipset support later coming, DDR mating with the Pentium IV eventually came.
Pentium IV's, as you might expect, were and still are on the expensive end of things. The new core was quite big when compared to other processors and the cost to product it was innately higher. In early 2002, Intel announced a new edition of the Pentium IV based on the Northwood core. The big news with this is that Intel leaves the larger 0.18 Willamette core in favor of this new 0.13 micron Northwood. This shrunk the core and therefore allowed Intel to not only make Pentium IV's cheaper but also make more of them. The core is still bigger than that of the Athlon XP, but this is explained by the fact that Intel increased the L2 cache from 256 KB to 512 KB for Northwood. This raises the transistor count from 42 million for Willamette to 55 million for Northwood. Northwood was first released in 2 GHz and 2.2 GHz versions, but the new design gives P4 room to move up to 3 GHz quite easily. It was recently released at 2.53 GHz using a 533 MHz front side bus. Other than that, Northwood is architecturally the same as Willamette.
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