I want to know if there are any server operating systems that can make use of 2 processors. Thanks.
Pretty much any modern operating system (Windows, Mac OS, Linux) will make use of 2 processors. Some systems are limited when it comes to a much higher number of cores (for example, Windows 7 32bit is limited to 32 cores), but for "normal" systems this is not an issue.
Note that the fact that the SYSTEM supports multiple cores and/or CPUs does not mean that all the cores will be utilised effectively! To that end, your _applications_ would need to be optimised for the purpose, and at present, very few are.
Yes, just about all modern operating systems support multiple processors. to give a better idea on how many (cpu sockets, virtual cores, and logical cores (multiple cores) each edition of Windows Server since 2008, here is a great article: http://blogs.technet.com/b/matthts/archive/2012/10/14/windows-server-sockets-logical-processors-symmetric-multi-threading.aspx Windows Server 2012 can recognize up to 64 CPU sockets and 640 logical processor cores.
As Bruce said, usage of multiple processors especially in servers goes way back. For example the IBM AS/400 used to have 11 processors back in 1990/91?
Pretty much every operating system, be it Windows, Linux, BSD, OS X, supports them and can utilize them to a certain extend.
One downside is that in multi-CPU systems there is a certain waste of power solely for scheduling and communication e.g. to see which CPU is busy and which is not, which processors has excess memory that can be released etc.
This is one of the reasons why the technology is heading towards multi-core rather than multi-CPU systems. Scheduling is faster and less resource intensive between cores since it all happens on a single component, a single CPU chip.
The one problem that remains until today regardless of multi-CPU or multi-core systems is that services and application don't utilize them to their fullest and sometimes cannot utilize them duo to dependencies.
Basically you will never see a 100% increase in performance between a single-CPU/single-core and dual-CPU/dual-core system.
Most modern operating systems can do so and not only on the server. Windows supported multiple processors since at least NT Server 3.51 (the first SMP system I was respnsible for back in '98). Unix and its variants have supported multiple processors even longer. This was back when there were 2 (or more) physical processor chips on the motherboard, not just multiple processing cores on a single piece of silicon.
Windows Server and Processor Cores... (Part 1)
Best way to take advantage of maximum CPU usage is to install the hyper-V role in server 2008 upwards and have virtual servers allocate CPUs.
Better was us to run VMWare ESXi hypervisor first then host virtuals.