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Why does Hibernate have to be implemented?



 
 
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  #1  
Old June 4th 15, 02:16 PM posted to microsoft.public.windowsxp.general
micky[_2_]
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Posts: 926
Default Why does Hibernate have to be implemented?

Just as a matter of curiosity, Why does Hibernate have to be implemented
by checking a box in the Power options? Sleep is not like that. Off
is not like that. Restart is not like that.

Does this have something to do with public computers or shared
computers, that managers wouldnt' want these hibernated but wouldn't
mind sleeping them or turning them off?

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  #2  
Old June 4th 15, 03:23 PM posted to microsoft.public.windowsxp.general
Paul
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Posts: 18,275
Default Why does Hibernate have to be implemented?

micky wrote:
Just as a matter of curiosity, Why does Hibernate have to be implemented
by checking a box in the Power options? Sleep is not like that. Off
is not like that. Restart is not like that.

Does this have something to do with public computers or shared
computers, that managers wouldnt' want these hibernated but wouldn't
mind sleeping them or turning them off?


I don't really know. I can think of a few things, but
I wasn't able to find a good conspiracy theory page
with other good reasons. Most discussions of hibernation,
seem to center around turning it on and off, without
discussing why you might want to do that.

1) On a machine with 64GB system RAM, and an SSD drive to
hold the OS, reserving a large hiberfil.sys is a waste
of valuable storage space. People with hard drive storage
for C: on the other hand, would not care. If I can afford
to buy 64GB worth of DIMMs ($800 for good ones), I can
afford a 4TB C: spinning hard drive :-)

Usually, SSD boot drives are selected from the "small/cheap"
category, and putting aside 48GB for hiberfil, isn't all that
practical.

2) The hiberfil.sys is a snapshot of system memory. Only
memory the OS "knows about", is recorded (not every byte need
be captured, which is why the shutdown interval is relatively
fast). There could be passwords stored in there. There exist
options sometimes to erase files like that (like purging the
pagefile at shutdown), but I don't think the hiberfil is
necessarily covered.

When Windows starts, it writes the "header" section of
the hiberfil, but does not overwrite the body. Even after
many reboots, information captured from days before, might
still lurk in the later sections of the file. Only a hibernation
option writes the body of the hiberfil, and if one section
writes out a big image, a second hibernation writes only
a small image, the tail end of the big image is still available
for forensic analysis.

The process that writes the hiberfil at shutdown, it uses
lightweight compression. Which is why the hiberfil does not have
to exactly match the size of system RAM. Note that this is
problematic - if I put my mind to it, I could arrange a
pattern stored in system RAM, which cannot be fitted into
the hiberfile. The hiberfil compression scheme is making some
assumptions about the typical contents of RAM, and not the worst
case contents of RAM. So if a "villain" designs a test case
for hibernation, it would be possible to break it. And have
the hibernation attempt fail to find enough space.

3) Writing 48GB of compressed memory image to a rotating hard
drive, would make the computer shutdown time take forever.
Say the hard drive writes at 100MB/sec, 6GB per minute,
worst case it would take 8 minutes to complete hibernation.
(Worst case hardly ever happens in the real world.) At
the next startup, you would wait another 8 minutes.

So that's about all I've got in the way of ideas. I have
hibernation enabled on this machine, as it isn't a "big"
machine, and the issued involved aren't that significant.

HTH,
Paul
  #3  
Old June 5th 15, 03:24 AM posted to microsoft.public.windowsxp.general
Jeff Barnett[_2_]
external usenet poster
 
Posts: 298
Default Why does Hibernate have to be implemented?

micky wrote on 6/4/2015 7:16 AM:
Just as a matter of curiosity, Why does Hibernate have to be implemented
by checking a box in the Power options? Sleep is not like that. Off
is not like that. Restart is not like that.

Does this have something to do with public computers or shared
computers, that managers wouldnt' want these hibernated but wouldn't
mind sleeping them or turning them off?


Sleep IS optional - you can turn it off in the BIOS for example or by
picking/defining a power profile that says "never". You can assign
functions to the computer's restart/boot buttons also. Pulling the plug
from the wall (or the UPS) is just about the only absolute action in
this area.

The reason that hibernation is treated special is that it can consume a
lot of some resources (disk and some memory) while saving others
(power). It's a tradeoff that makes sense in some situations but not in
others so you are involved in the choice. Sleep is almost always a good
idea for a home computer but almost never for a full-time server so
different OS may have different defaults. Etc.
--
Jeff Barnett
 




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