How does increasing RAM effect laptop battery life on standby?

Question

Just a simple theoretical question:

• Does increasing the amount of physical RAM on a laptop affect the battery life while in standby?

I always thought the only real difference between hibernate and standby was that standby still had to power the RAM to keep memory and a tiny bit of CPU, while hibernation allowed the RAM to power off by dumping the memory on hard drive which would keep that data even when turned off (at the cost of time in transporting the data).

Answer 1

Yes, probably. Most RAM on laptops is dynamic RAM, which requires periodic refreshing in order for its charge not to leak away.

There are a couple of ways that laptops can reduce this:

1. They can have flash RAM: not a good option, since flash is slower, more expensive and generally more complex than dynamic;
2. They can swap ram onto the disk: usually not all can be swapped in this way, but if most can, then you need suffer no penalty from the extra RAM. Swapped RAM will take time to be restored when the laptop wakes up.

Modern laptops have a series of states of sleep, which means they store less and less in RAM unswapped.

Answer 2

It does affect battery life, as more hardware means more power to keep it running. However, the drain on your battery from being in sleep mode is negligible. RAM only uses a few watts of electricity to maintain its state, so it doesn't really matter how much you have.

Answer 3

It depends on the design of operation system. I think everyone know what is virtual memory and swap.

Many systems, do make a copy of data from memory into HDD, with a lowest priority the background, even there are still many memory available. This kind of design speed up the response time when system is running out of memory.

It swap anyway, but if you have more RAM, it will save some power to read swap from HDD back to memory as they are less willing to be "dirty".

In the case of hibernate, I am not sure how it has been done. Does hibernate copy everything data, including cache and which are already swapped into HDD? Or it does only hibernate the data which are not "available"?