Why is computer using so much Virtual Memory?

Can this help?

 

Each 32-Bit process under Mac OS X has a virtual address space of ((2^32) - 1) bytes. Each 64-Bit process under Mac OS X has a virtual address space of ((2^64) - 1) bytes. The Mac OS X kernel manages this virtual address space for each process. That means, you can have many processes, which use a certain amount of the above mentioned address spaces, which requires the appropriate amount of virtual memory. That is what you see in the 145 GB.

Under Mac OS X, the real virtual memory, is the so called swap memory (in your case 0 bytes).