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Title is pretty much self-explanatory. When I disconnect (take out) my laptop's battery for a few hours, then put it back in and turn my laptop on, I haven't lost any information. How is this possible?!? Is time of the essence here, or are there like "on-chip" power supplies that keep the HD supplied with power for a long time?

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Yes the laptop battery has beeen removed, the OS (Windows 7) has been shut off completely, the power plug has been removed, etc. All of what you said applies so far. – pnongrata Aug 9 '12 at 13:52
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Magnets don't need power. Magnets are magic... – Tom Wijsman Aug 9 '12 at 13:54
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Probably the same way VHS does.. You serious??? – Artem Ice Aug 9 '12 at 19:25
Thanks @Artem Ice (+1) - however I am talking about laptops here with hard drives ("HDs"), not VHS technology. I understand that VHS taps store all information in the form of slides! But computer are a more complicated beast an need to store more than just pictures, things such as config files, executables, libraries and more. This was at the heart of my question. Thanks again! – pnongrata Aug 9 '12 at 19:36

2 Answers

up vote 12 down vote accepted

There are two types of modern laptop hard drives, spinning plate and solid state. Both are non-volatile, and only require electricity to read or change the data. No electricity is required to keep the data stored.

In a traditional spinning disk platter, a very precise moving head permanently charges small precise parts of the platters to represent the individual bits of data. In a SSD, non-volatile flash chips are used.

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Note that data in the disk buffer can be lost if it hasn't been flushed before the power loss. So it's possible in certain circumstances for very recently written data to be lost. – cmh Aug 9 '12 at 16:13
@cmh What you say is true. However, once disk gets written to the Flash chips or platters, its permanently saved. To not confuse the person who asked, I should clarify that if all programs and the operating system are shut down properly, then the disk buffer and all other forms of disk cache and data buffers that were destined for the hard drive would be saved there permanently. – Justin Dearing Aug 9 '12 at 17:29
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@cmh: Yes, that is one reason why it's always recommended to properly shut down the OS, instead of just cutting power. During shutdown, the OS will tell the drive to write out its buffer, and wait for the drive to report completion. – sleske Aug 9 '12 at 17:29
up vote 10 down vote

If you're talking about a hard disk drive then you're misunderstanding how they work. A hard disk drive has spinning metallic platters. The information is stored magnetically and does not require electricity to remain "saved", only to be read or written.

If you're talking about a solid state drive, then you may wish to read the Wikipedia article on flash memory. Essentially it works the same was as the card in a digital camera or an MP3 player. Short electrical bursts are used to change bits of the memory, without requiring a constant power supply. If you're asking about an SSD drive, you may find the HowStuffWorks article on Flash memory or the eHow article on SSD drives interesting.

Compare those to RAM, (Random Access memory) which is what your computer uses while running and does require a constant power supply.

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