basis where server 140 appears as to its clients as a network file server or on a per block basis where server 140 appears to the clients as a directly attached disk drive in either situation server 140 may need to move large quantities of data about both internally and between its clients and its mass storage devices furthermore server 140 may not need to examine or modify individual bits or bytes but may simply be required to accept or deliver blocks consisting of for example 1 024 1k bytes 4 096 4k bytes or other numbers of bytes of user data this storage server application may be implemented by a computer system such as that depicted in functional block form in fig2 central processing units cpus 210 may control and coordinate the operation of various devices connected to system bus 240 under the direction of instructions stored in memory 220 disk 230 may contain other instructions and data that are not immediately required by the system in its operations the system can communicate with its clients through network adapters 260 and with its mass storage devices such as disks 150 through storage adapters 270 the system may also benefit from additional cache memory separate from memory 220 that may be installed on an add in card such as pci cache memory card 250 in operation the storage server may place user data on mass storage devices 150 for long term availability but to improve performance and throughput it may be beneficial to store or u201c cache u201d copies of the user data in memory 220 eventually memory 220 may become full of these cached copies of user data and a least recently used u201c lru u201d or similar algorithm may be employed to determine which cached data to remove.