The present invention provides an input and output device for computer system storage that can prevent a computer system being fatally damaged by a computer virus, and also provides a software execution method that by using the input and output device, enables trial software, trial data and mail data to be safely tried. For this, a virtual computer system is used that runs on a computer system. Writes to a hard disk in the virtual computer system are made via a disk cache, and whether or not data is transferred from the disk cache to the hard disk is controlled. Application program snapshot data created by the computer system is recorded on a recording medium that is substantially read-only or transmitted to a different computer system. The snapshot data from the recording medium is read or received by the different computer system and a processing by the application program is resumed in the state in which data transfer from the disk cache to the first storage has stopped.