This is the type of DNA replication where the new strands of DNA are made from the old strands which are called templates. So, from two strands you get four. One new strand paired with the old...
Semi conservative. The double strand splits into two strands and then a strand is replicated from the template of the two strands constructing four total strands. Two original and two copies.
According to the conservative mode, of the two double helices formed one would be entirely of old material and the other entirely of new material. Thus the old parent double helix would be...