Adhered particles (foreign matters and dust) cause "defective products" or the "breakdown of devices", etc. on production sites. Although these problems can be solved if production is carried out in a clean room, this incurs considerable initial and running costs, hence attracting the interest in the enclosed clean space system.

A computer which has been freshly installed with its operating system and software obtainied from trusted software distribution media. As more software and configuration are added to a computer, it becomes increasingly difficult to determine if the computer is 'clean' or has been compromised by viruses, trojan horse or misconfiguration which reduces the security of the system.