The Cisco ASR 9000 Series has a modular power architecture available in both AC and DC. The power supplies are housed in field-serviceable power entry modules (PEMs), which also come in AC and DC forms. Each PEM can hold up to three or four modules depending on its corresponding type, with no power zones or placement restrictions (mixing of AC and DC supplies is not supported). Service providers can add more power as their bandwidth and feature requirements increase over time, by adding more line cards to the chassis. This capability translates to lower CapEx initially and optimal OpEx over the product life.