a. Disk caching is a technique that is used to speed up disk access by holding blocks of disk in memory. Discuss strategies that could be used to improve system performance with disk caching.

b. The time of write back for files that have been altered depends on the system. Some systems write back a file immediately when it has been altered. Others wait until the file is closed or until the system is not busy or until activity on the particular file has stopped for a given period of time. Discuss the trade-offs between these different approaches.