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Comment by free652 | Hacker News Reader

Windows loves to cache and "prefetch" apps, I still need to figure out how to disable prefetching since I have a very fast SSD.

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Memory is still an order of magnitude faster than your “very fast SSD”.

And memory is still an order of magnitude more expensive than SSD, per GB.

I just bought 4 GB of PC-6400 for a laptop at £40. A fast 128GB SSD is £100.

Summary: use RAM judiciously

All the more reason for your OS to use memory aggressively. Surely you don't want your expensive investment sitting around just doing nothing?

Unused memory is wasted memory.

The prefetched data is managed by the OS. If a program needs the RAM, the prefetched data is immediately discarded. Prefetching never creates RAM pressure.

This. It blows my mind how many people who write software don't understand how OS caching and virtual memory work. They are great filter interview questions ;)

just one?

At least one. Potentially more. The actual multiple depends strongly on the specific SSD and memory configurations in question, and on the benchmark of interest.

Instructions for Win7. http://www.tomshardware.com/reviews/ssd-performance-tweak,29... Why not leave it on, though? RAM is still faster than SSD.

Why? All it does is make it go faster.

And drain your battery for no reason.

Do you have any proof of that? "Free" memory uses as much energy as "used" memory, there is no distinction in SD|DDR-RAM. And if the OS is smart, it only has to keep a simple index of memory pages still relevant. I'd argue that this has a measurable battery-hit.

You're only accounting for the RAM power. Accessing the SSD costs power, too.

Then I think I'd rather Windows prefetched my programs while I'm plugged in so it doesn't have to do so when I'm on battery.

> You're only accounting for the RAM power. Accessing the SSD costs power, too.

A typical modern SSD reads at 500 MiB/s, consumes 3 watts when reading, and 0.3 watts when idle.

A stick of DDR3 RAM consumes about 3 watts, just sitting idle.

The power consumption from prefetching is minor compared to that of the RAM.

Reading from the SSD to laod it into RAM does drain battery. No idea if it is enough to matter though.

Windows7 are SSD aware. You dont have to do anything about it.

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