Identification
A digital video recorder (DVR) operates very much like your desktop computer, using a hard drive that records data (your programs) and erases it without the degradation of quality you may remember when you recorded over shows on a VCR tape. DVRs have five primary components that make them work like a computer: motherboard, through which all data flows; processor chip, the "brains" of the operation; hard drive, where information is stored; random access memory, or RAM, which is temporary memory; and read-only memory, or ROM, which stores data that can't be modified.
Read-Only Memory (ROM)
ROM is activated when you turn on the DVR, and this supplies the information necessary for the system to identify itself. The look of your menus, how they work, where you are allowed to navigate, how the system interacts with the remote control is stored here and generally doesn't change. Some of this type of information is also stored in a small section of the hard drive that is partitioned off and inaccessible to you.
Normal Operation
During normal operation, your DVR takes the data stream coming into it (the television programming) and runs it through the RAM, a type of memory that typically changes constantly, being written, read and overwritten, sometimes in a matter of just seconds, rather than storing data long term, such as on a hard drive. From the RAM chip, data that is being watched on the television will be written onto your hard drive if you are recording. If you are not recording, the data being written to your RAM eventually will be erased by subsequent incoming data.
Unplugging the DVR
When you unplug the DVR, power leaves the system. RAM requires power to store data and without it, everything the DVR was recording at that moment will be "forgotten" or lost. However, everything that had been recorded (stored on your hard drive) is saved. No power is required to keep data on a hard drive intact. The same is true with data on the ROM; the DVR will remember operate even after it has been unplugged.
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