指的是断电以后考勤机能保存内部已存储数据的时间段，通常保存时间越长表明考勤机性能越好，其安全可靠性变越高。
而卫星在接收到信息后也要先将数据保存一段时间，直到绕到能送回地球的那一刻。
After receiving the data, that satellite would hold the information until it could be sent on the next hop towards Earth.
尽管DB 2 PE的历史数据只保留较短的时间(几小时或几天)，但是一旦数据被保存在PWH中，这些数据便可在很长的时间内用于报告和趋势分析。
While the history data of DB2 PE is only retained for a short time (hours or days), once data is in the PWH, the data is available for reporting and trend analysis over much longer periods.
但是最简单的数据库并不要求使用所有允许的类型，通常只需要保存数值型、字符型和日期(或时间)数据。
But most simple databases don't require the full range of allowed types, and often they need to store only numerical, character, and date or time data.
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