Why Use Virtual Memory In Modern Systems?

Cyberhwk writes "I have a system with Windows Vista Ultimate (64-bit) installed on it, and it has 4GB of RAM. However when I've been watching system performance, my system seems to divide the work between the physical RAM and the virtual memory, so I have 2GB of data in the virtual memory and another 2GB in the physical memory. Is there a reason why my system should even be using the virtual memory anymore? I would think the computer would run better if it based everything off of RAM instead of virtual memory. Any thoughts on this matter or could you explain why the system is acting this way?"

Comments

Re:Memory exists to be used

[etymxris]

I've known this argument for many years, I just don't think it applies anymore. The extra disk cache doesn't really help much, and what ends up happening is that I come in to work in the morning, unlock my work XP PC, and I sit there for 30 seconds while everything gets slowly pulled of the disk. XP thought it would be wise to page all that stuff out to disk, after all, I wasn't using it. But why would I care about the performance of the PC when I'm not actually using it?

At the very least, the amount of swap should be easily configurable like it is in Linux. I haven't actually used a swap partition in Linux for years, preferring instead to have 6 or 8gb of RAM, which is now cheap.

rephrasing his question charitably...

[Trepidity]

I'd assume what he's asking is: in modern systems where the amount of physical RAM is considerably larger than what most people's programs in total use, why does the OS ever swap RAM out to disk?

The answer is basically to free up RAM for disk cache, based on a belief (sometimes backed up by benchmarks) that for typical use patterns, the performance hit of sometimes having to swap RAM back into physical memory is outweighed by the performance gain of a large disk cache.

Of course, OS designers are always revisiting these assumptions---it may be that for some kinds of use patterns using a smaller disk cache and swapping RAM out to disk less leads to better performance, or at least better responsiveness (if that's the goal).

Re:Would it help if

[Changa_MC]

I know it's not a good idea now, but this was seriously a great trick under win98. Win98 Recognized my full 1GB of RAM, but seemed to want to swap things to disk rather than use over 256MB of RAM. So I just created a RAM disk using the second 512MB of RAM, and voila! Everything ran much faster. When everything is broken, bad ideas become good again.

Re:You mean physical memory right :-)

[Reziac]

I've been running without a pagefile, in all versions of Windows, for about 10 years now -- on any machine with more than 512mb.

The only drawback is that a few stupid Photoshop plugins whine and refuse to run, because if they don't see a pagefile, they believe there is "not enough memory" -- a holdover from the era when RAM was expensive and the pagefile was a busy place. Sometimes I think about making a very small pagefile just for them, but have never actually got around to doing it.

Can't hibernate

[anomaly]

Windows makes me CRAZY about this. the OS is internally configured to use an LRU algorithm to aggressively page.

("Technical bastards" who question my use of paging and swap interchangeably in this post can send their flames to /dev/null \Device\Null or NUL depending on OS)

What I found when disabling paging on an XP pro system with 2GB RAM is that the system performance is explosively faster without the disk IO.

Even an *idle* XP pro system swaps - explaining the time it takes for the system to be responsive to your request to maximize a window you have not used in a while.

I was thrilled to have a rocket-fast system again - until I tried to hibernate my laptop. Note that the hibernation file is unrelated to the swap/paging space.

The machine consistently would blue screen when trying to hibernate if swap/paging was disabled. Enabling swap enabled the hibernation function again. Since reboots take *FOREVER* to reload all the crap that XP needs on an enterprise-connected system - systems mangement, anti-virus agent, software distribution tool, and the required ram-defragger which allows XP to "stand by" when you've got more than 1GB of RAM, plus IM, etc

I reboot as infrequently as possible and consider "stand by" and "hibernate" required functions. As a result, I live with XP and paging enabled, and tolerate the blasted system "unpaging" apps that have been idle a short time.

Poo!