What is the Windows Virtual Memory (page file)

What is the Windows Virtual Memory (page file) and what does it do?
The Windows Virtual memory is a place allocated on your hard drive (usually somewhere in the middle of the free space) that windows stores extra data from your RAM banks when that data isn;t being immediately used but may be needed in the near future. By default this file is not static and can grow or shrink within certain system-set limits. On most systems this is absolutely critical to system performance, but on higher end machiens with large memory banks it can actually slow the system up.

Well known Port Numbers

 21     FTP -- Control
22     SSH Remote Login Protocol
23     Telnet
25     Simple Mail Transfer Protocol (SMTP)
53     Domain Name System (DNS)
67      DHCP Clint
68      DHCP SERVER
80       HTTP
110     POP3
143     Interim Mail Access Protocol (IMAP)
389     Lightweight Directory Access Protocol (LDAP)
443     HTTPS
546     DHCP Client
547     DHCP Server

Desktop Support interview questions

1. Virtual Memory
when ever a program require more main memory, if your system doesn't have require memory, then system use memory from hard disk. But it is slow compare to main memory. data stored in virtual memory must be mapped back to main memory when ever it's to be used.