When a file is opened by a program, a filesystem lock is placed that prevents it from being accessed by another program. However, most programs in OS X will only truly “open” a file as a brief step in order to read its contents into memory. The file is then technically closed so it may be accessed elsewhere. Further interaction with the file will result in another quick “open” followed by the instructed manipulation right before the file is closed again, and computing goes on. Continue reading →