Currently Apple represents 20.5% of the 100 index and it is being reduced to 12.3%.
Other big names in the index are rising in weighting. Google will be up 1.6 points, Intel by 2.4, Microsoft by 4.9 and Oracle by 3.4.
None of this affects the values of the companies directly, but large shareholders, such as pension funds and hedge funds, have to adjust their holdings according to the index weightings. These trades will take place over the next few weeks before the revised weightings come into force on May 2. On the face of it, this could lead to a temporary sell off in Apple stock but it will be a technical sell rather than one based on fundamentals. Some analysts will be tempted to read more into this than is there.
Source: AppleInsider.