1. A method for establishing and maintaining a key-accessed file management organization and procedure in a computer system which includes a primary and secondary memory, said method comprising: providing a data level including a set of blocks of pages stored in the secondary memory; providing an index level stored in the primary memory when the file is in use; said index level including a set of index entries, each of which includes a starting address indicating the location on the secondary memory where a block of contiguous pages begins; and a size field indicating the number of pages in said block of pages having said starting address; said method further comprising maintaining the file by: changing the number of pages in said blocks as the size of the file changes, specifying said size in the size field as the logarithm, base two, of the number of pages referenced by said index entry, and changing the size field in any index entry in which the number of pages in the referenced block is changed.