Is the concept of virtual memory obsolete?

[jtr1962]

Looking at the latest offerings while researching the PC for my brother has led me to one conclusion-that the idea of virtual memory, paging to disk, or whatever other names may have been used, seems to be obsolete. I disabled the page file on my machine when I installed XP. I only had 1GB at the time. It didn't seem to hamper anything. Now that I have 3GB paging would be even more useless.

Anyone else agree that in this era of cheap RAM the whole concept of using your hard disk for extra RAM is obsolete? This is especially true of XP with its 4GB total limit on memory (physical and virtual combined). My brother's new PC will have 4GB physical RAM. XP wouldn't even be capable of addressing anything beyond that, whether disk-based or physical. This isn't even getting into the fact that few users will actually ever be using more than 2GB, at least with current software. I think I may have once or twice so far. Carrying this a bit further, should it be needed, installing even 16GB physical RAM isn't totally cost prohibitive these days (but you need 8 slots since 4GB DIMMs are still as sparse as hen's teeth).

 

[ddrueding]

Photoshop

 

[jtr1962]

Photoshop

Yeah, but my point is that if the OS is incapable of addressing more than 4GB (physical and disk combined), and you already have 4GB physical memory, then there's nothing to be gained with a page file.

Let me just state for the record that I've always hated the idea of page files. They were probably a necessary evil until 512MB-1GB became common. However, the sound of the disk churning away annoyed me no end. I also couldn't help but think that all that disk activity had a detrimental effect on drive longevity. In general I always disable things which require constant disk access. For example, the MS Office "findfast" feature is both practically useless, and the constant disk activity very annoying. The indexing or whatever XP does periodically with NTFS volumes every minute or so is equally annoying so I disabled it.

On the other hand, using disk as memory may suddenly make sense again once SDDs become mainstream, and you have software requiring tens of gigabytes (photorealistic games?).

 

[ddrueding]

The OS can address more than 4GB of memory if page files are factored in. Physical RAM is limited to <4GB.

 

[timwhit]

The OS can address more than 4GB of memory if page files are factored in. Physical RAM is limited to <4GB.

I have read this before, but I have found that when my commit charge goes above 4GB, things in Windows stop functioning normally. Explorer windows lose their menus, I can't open new windows, etc.

 

[ddrueding]

Perhaps we've finally found something that Vista does better? When I give my computer a good thrashing, it stays responsive and everything still works.

 

[jtr1962]

You've actually had times where you were using >4GB of RAM? Honestly, given how cheap RAM is these days, if I started regularly using a page file I'd probably just buy more.

Just for kicks I tried enabling the page file. Windows wouldn't let me set it larger than 3GB (the amount of physical RAM in my system), and insisted on locating it in the boot drive despite my settings to the contrary. When I restarted my system one of my dlls failed to load. Sure, my commit charge limit was now at 6GB instead of only 3GB, but I wonder if anything useful was actually gained. Anyway, I promptly disabled it, and then had to manually delete the inactive page file upon rebooting.

Since XP has a limit of 4GB physical RAM, and limits the page file to the amount of physical RAM in the system, then the ultimate limit on virtual memory is 8GB. However, owing to stability issues the practical limit is only 4GB. So nothing is gained by a page file once you have 4GB physical RAM. On my machine I suppose I can have a 1GB page file if I want, but I've never even needed 3GB yet, let alone 4GB.

 

[ddrueding]

I'm at 4GB because I use 32-bit Windows. 64-bit Windows is a special kind of hell; Vista is much better than XP, but it's still a minefield.

 

[Stereodude]

Photoshop

Photoshop doesn't use Window VM / page file. It does it own virtual memory management outside of Window's. So, it doesn't matter if you turn off the Windows page file or not PS will still sack your disc for temporary storage.

 

[sechs]

Wow.

So all memory in Windows is virtual. You can't even stop disk paging; Windows will page directly from DLLs.

The fact of the matter is, if you don't use your page file, then all it does is use some space on your disk. If you do need it and it's not there... problems.

The amount of memory addresses that Windows can use has no bearing on the amount of total memory that it can use. Each application gets its own virtual machine and "sees" the whole memory space; Windows only needs those addresses to use real RAM.

Making your page file bigger doesn't give you more memory. It just gives Windows a contiguous bit of space on your disk to page data out of RAM. In essence, this allows Windows to have free RAM all of the time... but if you don't need it, it won't make a difference to you.

Windows x64 isn't a special kind of hell as far as memory is concerned. It sees and uses the 6GB in my system seamlessly.

Photoshop no longer uses its own virtual memory system. It still uses a temp file system (scratch disks), because, with good sized graphics, you'd never want to run that through memory, anyway; and it uses a backing-store system, where large chunks of its memory are both paged-in and paged-out, so that it can maintain a level of responsiveness. The latter, of course, requires a page file to page-out to.

 

[ddrueding]

Windows x64 isn't a special kind of hell as far as memory is concerned. It sees and uses the 6GB in my system seamlessly.

I didn't mean in a memory way, I meant in a general usability sort of way. Drivers and application compatibility specifically.

Not to derail too much, but do you know how Photoshop plays with larger amounts of RAM? Can it use it? Could performance improve with 8GB of RAM and a 6GB image?

 

[sechs]

Keep in mind that Photoshop is still a 32-bit app, and can only directly address 3GB of memory in Windows. I would presume that more memory would simply keep your system from bogging down... but I've never tried to manipulate an image more than a few gigs in size -- well within Photoshop's reach.

Photoshop is one application which could seriously gain from a 64-bit version, if only for the purpose of accessing more memory. Certainly, some of the filters would be faster in 64 bits.