Why RAM needs a steady supply of power
A computer’s working memory, or RAM, stores information as tiny electrical states. Unlike a file saved to an SSD, those states are not permanent: they fade when power is removed. Even when the processor and screen are mostly off, the computer supplies RAM with a small amount of electricity and periodically refreshes its contents, restoring signals before they weaken.
That lets the computer preserve the exact session it had open—documents, browser tabs, and the state of running apps—without writing everything to storage first. When you wake it, the system can resume from that live memory instead of rebuilding the session from scratch.
Sleep is a tradeoff, not a full shutdown
Keeping RAM powered uses more energy than turning the computer completely off, though typically far less than actively using it. The benefit is speed and convenience: the machine can wake quickly because its working state is still there. The cost is that sleep depends on an uninterrupted power source. If a laptop battery runs flat, or a desktop loses power, ordinary sleep cannot preserve information that existed only in RAM.
Some computers use a separate mode called hibernation. Before powering down, the system copies RAM’s contents to storage, which takes longer but can preserve the session without ongoing power. Others can switch to hibernation automatically when the battery gets low. The distinction matters: sleep keeps the session alive electrically; hibernation saves a snapshot so it can be restored later.
