The major difference between the two is speed. Pentium III processors have a maximum speed of 1.33 gigahertz while Pentium 4 processors can achieve maximum speeds of 3.46 gigahertz. Both Pentium III and Pentium 4 processors are from the earlier families of Pentium processors.
The difference in maximum speeds that can be achieved by the two processors has many consequences on the overall performance of a computer. Notably, when a computer installed with considerable memory utilizes the speed capacity of a Pentium 4, it will perform noticeably faster when processing applications such as graphics and numerical computing operations.
There are many other differences particularly in the technology, architecture and cache size occupied by the two processors. Pentium 4 processors have built-in “hyper threading” technology that allows them to simultaneously perform multiple tasks more efficiently. In terms of cache size, Pentium 4 processors have an average size of 512 kilobytes, while Pentium III is capable of 256 kilobytes on average. Pentium 4 processors are considerably smaller than Pentium III, and so the latter normally takes up more space on the motherboard. The data bus architecture of the two processors is different as well. Pentium III has a data bus with maximum capacity of 133 megahertz, while Pentium 4 is capable of up to 400 megahertz.