增量备份
Time Machine compares all later backups to the first one. If you change a file since the last backup by adding, moving, or changing it,Time Machine backs up the whole file. If you delete a file, Time Machine tracks that deletion.
时间机器每次备份都会和前一次的备份文件做比较。如果从上次备份后，你更改过（移动，增加，修改）文件，时间机器将把这整个文件进行备份。如果你删除一个文件，时间机器将记录这删除的记录。
Because Time Machine makes a backup of files that have changed since your last backup, you should understand how some of your applications store files. Entourage, for example, stores its message information in a single database file that can grow very large over time; receiving a single email changes that database.
自从上次备份后，你更改过的文件，时间机器将把这个文件再次做备份。例如，存储一个信息在一个单一数据文件中，它可能随着时间变得非常巨大；收一封邮件将改变这个数据文件
Time Machine then backs up your Entourage database file, possibly several gigabytes in size, just to record the relatively small change of a email; this can quickly use all backup space. You might want to exclude these types of files from your Time Machine backup list and use a different method to back them up.
然后时间机器将备份你的邮件数据文件，可能要占据几g的空间，而只是为了备份一封很小的邮件；你可以从时间机器的备份清单里排除这类文件，选择其他的方式备份他们。