Cache as an intermediate component serves for storing content which has been requested by user and will be potentially used in the future. The cache capacity is limited, thus we cannot store all requested content. We have to use algorithms which mark an old content to be replaced in the cache. These algorithms are commonly named cache or caching policies. Optimally, the caching policy should replace the content which will not be used in the near future. First goal of this paper is to present a cache simulator which serves for comparison of caching policies. In a simulation, requests for data are produced by random request generator or can be generated from a log file. The second goal of this paper is to present results gained from simulations of different caching policies applicable to mobile devices and other clients in order to choose most suitable one.

Need of storing a huge amount of data has grown over the past years. Whether data are of multimedia types (e.g. images, audio, or video) or are produced by scientific computation, they should be stored for future reuse or for sharing among users. Users also need their data as quick as possible. Data files can be stored on a local file system or on a distributed file system. Local file system provides the data quickly but does not have enough capacity for storing a huge amount of the data. On the other hand, a distributed file systems (DFS) provide many advantages such as reliability, scalability, security, capacity, etc. In the paper, traditional DFS like AFS, NFS and SMB will be explored. These DFS were chosen because of their frequent usage. Next, new trends in these systems with a focus on increasing performance will be discussed. These include the organization of data and metadata storage, usage of caching, and design of replication algorithms. This paper provides overview of existing algorithms which are used in DFS. Described algorithms can be used as a basis for any future work.

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A cache stores data in order to serve future requests to those data faster. In mobile devices, the data have to be transferred from a server through the mobile network before being stored in the cache. The mobile network is prone to failure caused by users' movements and by the placement of base transceiver stations. Moreover, the mobile devices use various telecommunications technologies and therefore the speed of the network is highly variable. Using a cellular network for communication is also expensive. The cache is an intermediate component which addresses this problem. Once the data are downloaded, they can be stored in the cache for possible future reuse. When using a cache, the system designer presumes that the data will be requested again in the future. On the other hand, the original data stored on the server can be changed. Then, the cached data are in an inconsistent state. In this paper, authors present an adaptive method for maintaining the consistency of cached data which saves network traffic by reducing the number of messages needed for inconsistency detection.