Celeron chips have a smaller L2 cache 9128kb compared say with 512kb in the Pentium 4 Northwood, which translates into slower processing speeds. Celerons have a clock speed limit of about 2.0GHz, where as the Pentium is capable of speed in excess of 3.0GHz. Another difference is the Pentium runs at a lower core voltage because it is more energy effecient.
