"Here's an article that details the entire performance tab. FTA:
Physical Memory (K) The total physical memory, also called RAM, installed on your computer. Available represents the amount of free memory that is available for use. The System Cache shows the current physical memory used to map pages of open files. Kernel Memory (K) Memory used by the operating system kernel and device drivers. Paged is memory that can be copied to the paging file, thereby freeing the physical memory. The physical memory can then be used by the operating system. Nonpaged is memory that remains resident in physical memory and will not be copied out to the paging file."