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I am thinking of buying a SSD for my laptop, mainly for the purpose of extended operating time when running on battery.

At the moment I use a Hitachi HTS545032B9A300 (320GB) (Datasheet) as main drive and a Seagate Momentus 5400.3 120GB as secondary drive. I dualboot Windows and Linux but I don't need the windows partition any longer, a 120GB SDD would be more than sufficient space-wise.

Speed is not an issue for me, I make heavy use of tmpfs (ramdrive) within Linux and transfers of bigger files are mainly through some network filesystem anyways, thus a cheaper SSD should do. For the purpose of comparison I chose the OCZ Vertex Plus 120GB.

Power consumption always is a big promotional thing the industry uses to make me want to buy their SSDs, some sheet on the OCZ page provides an astonishing comparison of desktop HDDS and SSDs. The numbers I got comparing my laptop HDD and their SSD were not really astonishing any longer.

Hitachi 320GB HDD: 
  Startup (W, peak, max.)     4.5
  Seek (W, avg.)              1.7
  Read / Write (W, avg.)      1.4
  Performance idle (W, avg.)  1.3
  Active idle (W, avg.)       0.8
  Low power idle (W, avg.)    0.5
  Standby (W, avg.)           0.2
  Sleep                       0.1 

  1.5W active
  0.3W standby

I see that there are differences, but actually they don't seem that high as I though they were. And compared to the power consuption of the rest of my system I wonder if it makes a difference at all.

Have I just taken the wrong look at the whole thing or may I be better off to buy another battery for my laptop?

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Looking at those specs, I would probably think it would see more battery savings in idle time. I've never bought an SSD for battery savings though, only performance. I'd love to hear what other experts may say – Canadian Luke Jun 7 '12 at 16:12
I am not really sure that the definition of standby is the same for HDD and SSD. I guess standby for SSD is comparable to idle for HDD, but thats just a thought. – Baarn Jun 7 '12 at 16:25
Standby for the SSD is essentially equivalent to everything from Performance Idle to Standby for the hard drive. So in a situation where the hard drive would be in Standby the SSD would also be in Standby, and in a situation where the hard drive would be in Performance Idle the SSD is in standby. – Mr Alpha Jun 8 '12 at 10:28
If all you care is power consumption, take at look at SanDisk SSD's, AFAIK they have the lowest. – jgillich Aug 13 '13 at 9:48

Although the numbers don't look inspiringly different, here are a couple of things to consider:

First, the startup consumption is going to be a bigger part of a HDD than you would think - in order to save power, the disk spins down a lot and hence has to spin up a lot. There will be a lot of these spikes as you use the disk on an ongoing basis.

Second, consider the duration of the usage. The SSD will essentially be on/off - you request a read or a write, it services it, done. The disk will need to (potentially) start up, seek, read/write, spin down. It will be orders of magnitude slower. When running on a battery the quicker you can complete an operation and stop using the device draining power, the better - the SSD is going to win, hands down.

I won't even get into readahead semantics and random versus sequential IO, suffice it to say: the more random and sporadic your disk access is, the better the SSD is going to do. If the laptop is permanently on, reading and writing, with no down time then the difference will not be that great but that is not really a typical usage profile for a laptop.

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I had these thoughts, too, but I wonder if this effect is measurable and worth it (10 minutes more battery are not worth an SSDs price). – Baarn Jun 7 '12 at 16:47
Ah, right - from that perspective, it would likely be more economical to just buy a bigger/replacement battery. Taken as the sole benefit, I agree with you, it is not worth it. However, as someone that took the SSD plunge a couple of years ago at a huge premium (they have reduced significantly in terms of cost since then), once you get used to the performance you will never, ever, go back to a spinning disk. Once I had my laptop upgraded my desktops soon followed - it was too painful otherwise (and the desktop had a RAID array). – Adam C Jun 7 '12 at 16:51

If you have extra money then its your choice but if you are a money saver then I will not recommend you to SSD for just increase battery life as it can increase only 10-15 minutes and only some selected models and brands do that not all. But if you care about some more things like Bootup Time for Windows 7, noise, vibration, Heat Produced, Failure Rate, File Copy / Write Speed, encryption, File Opening Speed, Magnetism Affected then SSD is the better choice.

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