COMPONENTS ARE IN LIGHTWEIGHT MODE

HI ALL,
WHEN I OPEN AN ASSEMBLY (WITH 260 COMPONENTS) SOME OF THE PARTSARE IN LIGHTWEIGHT MODE. I COULD NOT FIND WHATS THE REASON.

THE TASK BAR OF SOLID WORKS SAYS "LARGE ASSEMBLY MODE". WHY IS ITSO?

I AM USING SW2007

REGARDSSolidworksAssemblies