Abstract: It is provided a computer system comprising a storage device storing a file, application computers and a management computer for executing a management program. The management computer manages fragmentation definition information indicating a manner of allocation of data of the file and file management information for managing the state of allocation of the data of the file, and allocates the data of the file stored in the storage device to a distributed memory storage in accordance with the fragmentation definition information. The application computers executes an application program and an access management program. The application computers, by executing the access management program, receives an access to data of the file from the application program, obtains the file management information about the file to be accessed from the management program, and accesses the data allocated to the distributed memory storage on the basis of the file management information.