A preload library partitions certain files into segments and transforms the data of the files on a segment by segment basis, each independently of the other. The transformed segments are then stored as part of a transformed file, with each segment corresponding to a bag containing a chunk (of transformed data) and a gap which permits the chunks to grow when data of the segment is modified during a write operation. The bags are followed by a chunk map which contains metadata defining the compressed version of each segment. The preload library intercepts system calls from applications to the OC specifying access to specific segments of a transformed file. The preload library identifies the chunks corresponding to the specified segments, retrieves and reverses the transform on those chunks and passes the data to the application requesting it. For a system call to write data to certain segments, the data is modified and re-transformed by the library before being written back to disk. A preload library provides improved random access into transformed (e.g. compressed, encrypted, etc.) files.