popularity of blade servers, and their own appetite for power, has led to an increase in the number of rack-mountable uninterruptible power supply (or UPS) units, including units targeted specifically towards blade servers (such as the BladeUPS). Cooling During operation, electrical and mechanical components produce heat, which a system must dissipate to ensure the proper functioning of its components. Most blade enclosures, like most computing systems, remove heat by using fans. A frequently underestimated problem when designing high-performance computer systems involves the conflict between the amount of heat a system generates and the ability of its fans to remove the heat. The blade's shared power and cooling means that it does not generate as much heat as traditional servers. blade-enclosures feature variable-speed fans and control logic, or even liquid cooling systems that adjust to meet the system's cooling requirements. At the same time, the increased density of blade-server configurations can still result in higher overall demands for cooling with racks populated at over 50% full. This is especially true with early-generation blades. In absolute terms, a fully populated rack of blade servers is likely to require more cooling capacity than a fully populated rack of standard 1U servers. This is because one can fit up to 128 blade servers in the same rack that will only hold 42 1U rack-mount servers. Networking Blade servers generally include integrated or optional network interface controllers for Ethernet or host adapters for Fibre Channel storage systems or converged network adapter to combine storage and data via one Fibre Channel over Ethernet interface. In many blades, at least one interface is embedded on the motherboard and extra interfaces can be added using mezzanine cards. A blade enclosure can provide individual external ports to which each network interface on a blade will connect. Alternatively, a blade enclosure can aggregate network interfaces into interconnect devices (such as switches) built into the blade enclosure or in networking blades. Storage While computers typically use hard disks to store operating systems, applications and data, these are not necessarily required locally. Many storage connection methods (e.g. FireWire, SATA, E-SATA, SCSI, SAS DAS, FC and iSCSI) are readily moved outside the server, though not all are used in enterprise-level installations. Implementing these connection interfaces within the computer presents similar challenges to the networking interfaces (indeed iSCSI runs over the network interface), and similarly these can be removed from the blade and presented