if we do not use any wallpaper on desktop will it increase performance of windows?
I've never seen wallpaper adversely affect performance on the machine itself, but when connected to the machine from a remote desktop connection it certainly can. The bitmaps that get sent across in a terminal session are much smaller with just a solid color background.
I suppose with really low-grade video hardware or a buggy video driver you could see downgraded performance.
Rarely I've seen wallpaper be repainted slowly after a maximized window was minimized, but that's usually when there are a ton of things going on on the server that consume considerable amounts of system resources.
If you are using some kind of remote access (via network / internet), then turning off the background will increase the transmission speed of your desktop. From my experience, a background image effects the performance very little (unless your running a netbook with little memory or something). It will chew through a bit of memory however, a 32bit 1920x1080 image will consume a bit over 8MB of RAM (not much of an issue of you have 8GB, but might be an issue if you have 512MB or less)
It can certainly have an impact on a machine with virtual memory, in my experience. (That's the default and how most machines run, although for newer machines with multigigabyte RAM there is a good case for disabling it.)
The problem is that Windows likes to swap ‘unused’ memory out to the pagefile even when there's no real need, there being memory to spare. That's normally not a problem, except for if you're working in a full-screen application window, your background image isn't being rendered; its memory becomes unused and gets swapped out to disc. Then when you finish working and unmaximise the window, it suddenly becomes needed; several meg of rendered background then has to be dragged back off the disc and copied back onto the screen. On older, slower machines like laptops this was very noticeable.
This was the case for WinXP; it may have changed in Vista/7 since, due to the increased usage of video-card-accelerated rendering.
This answer from another question explains it fairly well: Logging in to Windows 7 with one specific user account is very slow. Why?
It seems that having a solid colour desktop slows down the login time on Windows. Yes, this even affects Windows 7, so its not just a problem with older OS's.
I am interested in this topic so I test it on the virtual machine. I have archlinux with LXDE desktop on VMware, I assign 500M RAM to this system, therefore I care much about the memory useage.
when I use a 600k png file as the wallpaper, the memory use is about 139M.
when I use a solid background, the memory use is just 122M.
I tested on two fresh start separately and use the
htop command at about 2min after the start.
The conclusion is that with wallpaper addtional memory will be needed, the cpu is hardly affected. If you have a very small memory, you may care about the performance.