Features of the new Beast
While we have given you an explanation in our past Pentium 4 reviews on what this processor has in the way of new features over the Willamette, Pentium 3 and Athlon XP processors, we feel that opening two reviews at once is a hassle. So here it is for you again, and for those of you who haven't seen a Pentium 4 review before, here is your chance to brush up on what everyone is talking about.
- Cache Increase over Willamette
The Intel Pentium 4 Northwood CPU has stepped up the L2 cache from 256KB of Advanced Transfer Cache, or ATC as it is known, to 512KB, running at the same speed as the CPU core. This gives the Northwood a clear advantage for high memory usage, especially when using DDR SDRAM and SDRAM model mainboards. While the L2 cache has grown over the Pentium 4 Willamette processor, the L1 cache has remained the same size.
- Netburst Bus Interface now at 533Mhz
For most of the past three years, Intel has been relying on the P6 bus used by the current P3 and Celeron range. While this bus has been easy to overclock and very stable, it doesn't have the scalability that is required for future processors. Intel finally decided to step away from the P6 architecture and introduced the new Pentium 4 400MHz QDR FSB. The well-known 'FSB' of Pentium 3 is clocked at 133 MHz and able to transfer 64-bits of data per clock, offering a data bandwidth of 8 bytes * 133 million/s = 1,066 MB/s. The Pentium 4's system bus is only clocked at 100 MHz and also 64-bit wide, but it is "Quad Data Rate" using the same principle as AGP 4x. The new bus can transfer 8 bytes x 100 million/s x 4 = 3,200 MB/s. This is obviously a tremendous improvement that even leaves AMD's EV6 bus far behind. The bus of the most recent Athlon is clocked at 133 MHz, 64-bit wide and "Double Data Rate", offering 8 bytes x 133 million/s x 2 = 2,133 MB/s. With the move to 533Mhz FSB, Intel has effectively increased the CPU to System communications bus to 4.2GB/s, the fastest that any processor has ever been.
Intel's Pentium 4 CPU is paired with the i850e chipset, a Dual Channel RDRAM solution. The i850 has two independent RDRAM channels, which can deliver up to 3.2GB/s max memory bandwidth when used with four RIMM modules. While RDRAM is able to produce such high bandwidth, its memory latency problems and high prices make it practically a dead issue for the home consumer. To this end, Intel and other third party vendors have started to produce SDRAM and DDR SDRAM solutions to provide the Pentium 4 with lots of memory bandwidth goodness. Introduction of the I845PE and GE have made the Intel Pentium 4 processor more affordable to the average user.
- Rapid Execution Engine
Another feature of the Pentium 4 which is unique to Intel is the Rapid Execution Engine, or REE for short. The REE works on the principal of two double pumped ALU's and two double pumped AGU's. This allows for the engine to process 2x the amount of a P3 or Athlon CPU. But the story looks a lot different for the instructions that cannot be processed by the rapid execution units. Those instructions, or µOPs, need to use the one and only slow ALU which is not double pumped. The majority of instructions need to use this path, which obviously sounds scary. However, the majority of code is in actual fact consisting of the most simple 'AND', 'OR', 'XOR', 'ADD' instructions making Intel's "Rapid Execution Engine" design sensible, though not particularly amazing. This feature has remained unchanged from the Willamette to the Northwood.