Tiếp theo, chọn cơ sở dữ liệu cần thiết và nhấn nút 'Restore' để bắt đầu MS Exchange Server phục hồi hoạt động. Quá trình khôi phục lại (khôi phục lại từ "máy tính địa phương của MS Exchange Server) sẽ mất một khoảng thời (phụ thuộc vào kích thước tập tin khôi phục của bạn). | 368 INPUT OƯTPUT CHAP. 5 --------------- s f 7 2 Time - a - - I H ------------------------------ 0 T 2 T Time b Figure 5-51. a Running at full clock speed. b Cutting voltage by two cuts clock speed by two and power consumption by four. In a similar vein if a user is typing at 1 char sec but the work needed to process the character takes 100 msec it is better for the operating system to detect the long idle periods and slow the CPU down by a factor of 10. In short running slowly is more energy efficient than running quickly. The Memory Two possible options exist for saving energy with the memory. First the cache can be flushed and then switched off. Il can always be reloaded from main memory with DO loss of information. The reload can be done dynamically and quickly so turning off the cache is entering a sleep state. A more drastic option is to write the contents of main memory to the disk then switch off the main memory itself. This approach is hibernation since virtually all power can be cut to memory at the expense of a substantial reload time especially if the disk is off too. When the memory is cut off the CPU either has to be shut off as well or has to execute out of ROM. If the CPU is off the interrupt that wakes it up has to cause it to jump to code in a ROM so the memory can be reloaded before being used. Despite all the overhead switching off the memory for long periods of time . hours may be worth it if restarting in a few seconds is considered much more desirable than rebooting the operating system from disk which often takes a minute or more. Wireless Communication Increasingly many portable computers have a wireless connection to the outside world . the Internet . The radio transmitter and receiver required are often first-class power hogs. In particular if the radio receiver is always on in order to listen for incoming email the battery may drain fairly quickly. On the other hand if the radio is switched .
