(Approx. 908 words)

Shut down, Sleep, Hibernate - Which one, when and why?
By Phil Sorrentino, President, Sarasota PCUG, Florida
November 2011 issue, Sarasota PC Monitor
www.spcug.org
president (at) spcug.org

Shut-down is pretty straight forward, it removes power from your computer and ensures that the next time the power is turned on, the computer will go through the normal “boot up” process. Sleep and Hibernate are different and are “Powered Down” modes. The reason for using one of these powered down modes will differ depending on the type of computer, desktop or laptop, and the need to quickly get back to the operating mode after a pause in operation. Power usage, though always important, is mostly a consideration when using a laptop. How much operating time, before the batteries must be recharged, can be a big consideration for a laptop user. It can determine how useful the computer may be on a long flight, or how many movies the kids can watch on a cross-country road trip. Even with desktops, the increased cost of electricity can become a key factor for customers who are under pressure to manage their total cost of ownership (purchase price plus operating expenses). 

The hardware that makes up today’s laptops has gotten quite efficient and the Windows Operating System software’s ability to manage that hardware’s power usage has constantly been improved. One of the biggest improvements since the early 1990’s has been the addition of these power down modes, to help provide longer battery life. 

Improvements in battery technology has greatly increased battery capacity as well as battery lifetime. Besides improvements in battery technology, the Operating System control over the hardware can also improve the battery life. A job for the Operating System is to make the system as efficient as possible while still maintaining an acceptable user experience when turning the system on and off. (With the advent of Solid State Devices, in place of disk drives, we will eventually get to a very fast on and off experience. You can actually have it now, but it is very costly. By the way, try a tablet PC and see how fast it turns on and off; no moving parts in a tablet PC.)

The Windows 7 power management goals are simple:
1) make turning a computer off/on as reliable, simple, and fast as turning a TV off/on, and 
2) maximize the battery usage if on battery, and reduce the energy consumption if on A/C power.

The first goal involves changing the model for what "off" and "on" really mean. By now, most everyone knows that turning a TV off doesn’t really turn it off. It is still available to receive the remote control signal, so that it can come back on quickly. To the degree possible, "off" is really "sleep", in Windows. When a PC goes into the sleep mode, the system state is saved in RAM; part of that 2 or 3 Gigabytes typically available in modern PCs. This arrangement creates the best balance between speed of resuming operation, and lowest power usage.  

Currently, Windows 7 defines three power-down modes:
Sleep – a power-saving state that allows a computer to quickly resume full-power operation (typically within several seconds) when you want to start working again. Putting your computer into the sleep state is like pausing a DVD player—the computer immediately stops what it’s doing and is ready to start again when you want to resume working.
Hibernate – a power-saving state designed primarily for laptops. While sleep puts your work and settings in memory and draws a small amount of power, Hibernation puts your open documents and programs on your hard disk, and then turns off your computer. Of all the power-saving states in Windows, hibernation uses the least amount of power. On a laptop, use hibernation when you know that you won't use your laptop for an extended period and won't have an opportunity to charge the battery during that time.
Hybrid Sleep – is designed primarily for desktop computers, is a combination of sleep and hibernate—it puts any open documents and programs (the system state) into memory and onto your hard disk (so nothing can be lost if power goes out), and then puts your computer into a low-power state so that you can quickly resume your work. 
That way, if a power failure occurs, Windows can restore your work from your hard disk. Normally, when the user returns and “wakes” the machine, the system state is just restored from RAM, and the responsiveness to the user is fast. However, if for some reason power is lost (for example, if the PC is unplugged to move it - like you might move your TV), the system can still resume from the system state previously saved to disk with all context and data intact. (When Hybrid Sleep is turned on, putting your computer into sleep automatically puts your computer into Hybrid Sleep. Hybrid Sleep is typically turned on by default on desktop computers.) While Hybrid Sleep can be used on a laptop computer, it isn’t as applicable. A desktop is vulnerable to power loss, while a laptop can, of course, run on its internal battery. 

So, although there is a lot going on to produce and provide the power down modes, there really isn’t much to think about. For desktops, let it go into, or select, sleep (which should be hybrid sleep) and for laptops take advantage of hibernate (your battery will thank you).