The most notable difference between a Pentium 3 and a Pentium 4 processor is the speed. The Pentium 3 maxes out at 1.33 GHz while the Pentium 4 blazes up to a maximum of 3.46 GHz. But these processors have other characteristics that affect the performance and reliability of your computer.
Caches
The Pentium 4 processor has a cache size of 512 KB and up, while the Pentium 3 processor has about 256 KB and maxes out at 512 KB.
Size
The Pentium 3 processors were bulky and took up a lot of space on the motherboard. As with each new generation of the Pentium, the Pentium 4 processors are significantly smaller.
Technology
The Pentium 4 has "hyper threading" which allows the computer to multitask more efficiently and effectively.
Architecture
The Pentium 3 lacks the "NetBurst" architecture of the newer version. The Pentium 4 thus allows for advanced graphics, video and multimedia processing.
Bandwidth
The Pentium 3 had a maximum of 133 MHz and 64 bits wide bus with a peak bandwidth of 1.064 GB. The Pentium 4 has a maximum of 400 MHz with a 64 bit wide bus and a peak bandwidth of 3.2 GB
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