What is the difference between launching a program and opening a data file?

Answer 1

The actual launching of a program and the opening of a file are performed by the system. A user or a program can only request the operating system to do this.

When a program issues a request to open a data file, it also specifies the intended use of the file. Will it read, write or do something else to the file or the information in it; Will it be concerned if other programs access the file at the same time so that it will need exclusive access or can use for the file at the same time be shared. The system will then locate the file and determine If the requesting program and the person running it are authorized for the desired type of access to the data file. It will then setup a bunch of system tables to show that the file is available and to track its use and report back to the requesting program information making the file available.

When a user or a running program asks the system to launch a program, the system has to insure that the program named exists, is capable of running as a program, is the requestor authorized to have the program launched, and if system resources are available to set up the program, bring it into memory, and run it. If all this true, the program is setup to run and is started.