[ltp] the purpose or advantage of suspend and hibernation

[Bjorn Knutsson]

On 19 Nov 2003 05:35, Dennis D. Jensen wrote:
> Hello laptop-fellows,
> 
> What is the purpose or advantage of suspend and
> hibernation?
> 
> I realize it is a bit funny or odd question, but I've
> rarely seen anyone questioning it.
> 
> There is even many variations of suspend: suspend to
> ram, suspend to disk, etc. What is it about?

Well, the semantics of the different modes of suspension are
different.

> Why not just shutdown and boot again when needed? It
> doesn't take _that_ long, unless of course you run a
> fashionable GUI Desktop (I don't).

Sure, you could do that. Of course, that means that you lose your
environment, the content of your ramdisk, your command history etc. 
I'm running my window manager with 12 virtual workspaces, and at
times, I have things running in all of them. Different projects and
articles that I'm working on. Rebooting would mean I'd have to
re-populate them and figure out what I was doing.

At times, I don't reboot my laptop for months. If Thinkpads did not
support suspension and hibernation, I'd be looking for a new brand.

> What are the advantages? Under what circumstances will
> they prove useful or perhaps even necessary? Do they
> save power or something like that? Nay! How can they
> compared to shutting down of powering off!?

They save time, batteries and context. I use suspend to RAM for
short-term suspension, e.g. to save on the battery during a meeting
when I don't need the machine for 5-10 minutes, but also want to be
able to get back to what I was doing quickly. I also use it when the
machine is attached to A/C-power and I'm not going to use it for a
while, e.g. when I'm finished for the evening.

I use hibernation, aka suspend to disk, when going between home and
work, or when I'm out travelling and I expect the machine to be
suspended for a longer time. In the latter case, it saves the
batteries for when I really need them. The time to restore is longer,
but since the time I keep the machine suspended is longer, that's OK.

Also, using hibernation in these case saves the batteries. The
lifetime of laptop batteries depend on the number of charge-cycles,
and since there is a draw, albeit small, when suspending to RAM,
hibernating reduces wear and tear on the battery.

Finally, if you're travelling with multiple batteries, you can use
hibernation to suspend the system when you're swapping batteries. You
could of course do this by shutting down, swapping and rebooting,
but...

> Disadvantages? Right now I cannot see the
> advantages... A couple of common sense comments could
> help out here, please.

See above - loss of context, loss of (setup) time, and of course, it
takes at least as long as hibernating.

But your use of your laptop may be very different from mine, so feel
free to use shutdown+boot instead, if you feel that's superior. ;-)

/Björn