You seem to misunderstand some things.
Is there a way to make the computer use less RAM as the disk cache and
at the same time, allocate more memory for any other GUI resources,
file handles, TCP/IP sockets, and any other possible resources,
especially if the computer has more RAM, sometimes even 16GB nowadays.
Memory allocation (and, more generally, management) is done by the kernel of the operating system. The cached memory is used as what its name implies: as a cache. To be more specific, the kernel has decided that some data, even if not asked by processes, are better of kept there, due to that they may be frequently used/requested and the kernel finds it non efficient to do hard disk I/O.
Having said that, it simply is a cache. If the kernel finds that it needs to utilize more memory it may as well write the cache contents back to the hard disk and use the freed memory for other purposes.
I remember at some point, it was possible to set a computer more for
"desktop" tasks vs "server" tasks.
There is not much practical distinction - aside from processes each computer is running. People who want to use their computers as servers try to stop unneeded processes from running, so that more CPU time/memory is provided to the process they want to run.
Having said that, nobody stops you in your "desktop" machine from killing processes you don't want to be run so that more CPU time/memory is available to the other running processes.
So I think these are tweak-able numbers.
I may be wrong here, but seeing as this is done by the kernel of the operating system, I do not really think it's tweak-able.
I don't know about XP vs Win 7, but note that each OS might not be designed to be perfect. So at the time of Win XP, it might have been that even if they allocate resources, the pool was limited to a hard coded number, in the Registry, such as to 1GB or 2GB, when most of the machines at that time was max 1GB or 2GB of RAM. Even at some point, a partition in the hard drive cannot be beyond some size, such as 320GB or whatever it was, until the OS is improved to handle it. – nonopolarity – 2013-05-13T01:20:47.960
So you can't be so sure to say the resource pool can be as large as it is to grow automatically, particularly most PC were not above 8GB at the Win 7 era, but nowadays, it is so easy to get 12GB or 16GB or even 32GB or RAM. – nonopolarity – 2013-05-13T01:21:39.700