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 System
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 hits 800Mhz
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.
800Mhz has how become the turning point for Intel as a bridge between the Northwood and the upcoming Prescott CPU. At 800Mhz the Pentium 4 has a maximum theoretical bandwidth of 6.4GB per second. This allows the Pentium 4 to take full advantage of the Dual Channel DDR 400 memory.
- 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.
- SSE2, one massive performance boost
Intel's name for the Pentium 4's new design is "NetBurst". Like with the Pentium III and its SSE instructions, Intel is trying its hardest to push the idea that their new processor will make your web pages load quicker. Unfortunately, the Internet is mostly limited to your modem's maximum speed and the speed of your ISP. The average consumer, however, is not going to know this straight off and it is a perfect way to market the Pentium 4.
Another big issue with the Pentium 4's "NetBurst Micro Architecture" is its obvious focus to deliver the highest clock rates. Again, 'NetBurst' shows its roots in Intel's marketing department. While Intel in the past has said "MHz isn't everything", it seems that they are trying to ring that bell that they tried to cut down in the days of the Cyrix 6x86 CPU's. As many of you may know by now, the Intel Pentium 4 at the same clock speed can't beat an AMD Athlon in just about every benchmark today. While these benchmark programs aren't SSE2 optimized (yet), it does show that Intel is trying to focus more on the future and not on the present. This could be a very big marketing mistake with most of the hardware community staying away from expensive Pentium 4/RDRAM solutions at the moment. However, if you are one of the hardware junkies like me who have to have the fastest thing with the highest numbers on it, Intel has taken this crown and continues to do so.
- 128-bit SMDI Integer Enhancement
While the MMX and SSE technologies provided for a total of 68 64-bit Integer Instructions, Intel's SSE2 allows for 128-bit Integer instructions. This allows for 2x 64-bit instructions from SSE or MMX optimized software to be executed, or 1x 128-bit SSE2 instruction to be executed.