You can look them up in your system documentation. Much of the discussion will apply to most systems. A few system functions take more than one parameter or return something unusual. However, you could model the necessary function on the implementation included and do anything you wish. The most interesting use of the system is to read and write program and system files.
All disk accesses using system calls require a file control block.
This is a block of 32 bytes which contains file information. Seven bytes before the file control block and 3 bytes after it may also be used by some systems. Therefore you really need to allocate 42 bytes to a space for the file control block. The pointer to the file control block is actually seven bytes above its beginning. Each would have to be given a separate name.