5GB of a RAM does not look as good in computer sales advertisements. But, 6GB of RAM, or 8GB of RAM looks better on an PC ad, Many people are willing to spend an extra $20 to $50 money for 6GB to 8GB RAM. People may choose to buy a computer with 4GB and less RAM because it is cheaper than a computer with 5GB of RAM. Some PC motherboards may not have enough RAM slots to support 5GB of RAM if the motherboard only has four RAM slots which only support 1GB of RAM per slot, or newer motherboards with 2 RAM slot which only support 2GB of RAM per slot where both the motherboards only support a maximum of 4GB of RAM. There are also some older Intel Pentium 4 motherboards which may support only a maximum of 2GB of RAM because there are only 2 RAM slots on the motherboard, and each RAM slot can only use a maximum of 1GB of RAM per slot.