This paper was based on Helen's extensive review of work on temporal issues within the HCI and Psychology literature. The experienced user never has to devote conscious attention-directed awareness to the timing of interface behavior. Chris has taken aspects of utility theory, an important branch of economics, and applied it to the way retrieval delays affect user's perceptions of the value of information. Typically caching takes place at two levels. First the browser itself keeps copies on your local disk.
Proxy servers can allocate much more space to caching.
Also, because the proxy is used by many web clients, there is a good chance the page you want has recently been accessed by another user and is in the proxy's cache. Cristian and Maria described a caching mechanism based on more levels of proxy-like servers. They propose that the hierarchy of proxies should follow the DNS hierarchy given by the domain name of the machine. The advantage of this as a structure is that users within the same domain name grouping are likely to have similar access requirements. In contrast, a delay of even a few hundred milliseconds in the middle of an orchestral performance would not be acceptable, although an occasional loss of sound quality may be.