VAX/VMS: Virtual Address Extension/Virtual Memory System

VAX is an acronym for Virtual Address eXtension, a 32‑bit computer developed by Digital in the 1970's. The VAX architecture supports multiprogramming, where many users running different programs can use the VAX simultaneously and each appears to have full control of the computer's resources.

The multiprocessing VAX functions vary differently from the old timesharing systems, which would allocate a slice of CPU time to each user of the system in a rotating fashion, whether the time slice was required or not. The VAX/VMS environment, however, provides each user an allocation of processor time based on the user's needs and priority. If a user does not need his quantum of time, or a portion of it, it is given to the next user.

This scheduling method is very efficient when compared to the old method of timesharing. The VAX is capable of addressing more than four billion addresses, through a method known as virtual memory addressing. Because the memory is virtual however, there is no need to have four billion bytes of physical memory. The VAX executes programs by a technique known as paging, whereby a single "page"of the program is read into memory at a time, and when a new page is needed, the old one is "swapped" back out to disk to make room for the new one.

The VMS operating system ties everything together. The user interacts with VMS (Virtual Memory System) through a Command Language Interpreter (CLI), usually the Digital Command Language (DCL). When you use VAX/VMS, you are known to the system as a process, which is created when you log in to the system and deleted when you log out. This process carries with it various attributes to identify you from other system users (process name, identification, user identification code, privileges, etc).

Terminal Control Keys

Key	Result
Ctrl-A	Allows you to insert, rather than overstrike, characters on DCL command line that you're editing
Ctrl-B	Displays DCL commands that you've previously entered
Ctrl-C	Interrupts the running program or the program being executed
Ctrl-E	Positions the cursor at the end of the line
Ctrl-H	Positions the cursor at the beginning of the line
Ctrl-I	Tab
Ctrl-O	Alternately suppresses and continues the display of the output terminal
Ctrl-Q	Enables (toggles on) output to the display after CTRL-S
Ctrl-R	Retypes the current input line and repositions the cursor at the end of the retyped line
Ctrl-S	Disables (toggles off) output to the display until CTRL-Q is pressed
Ctrl-T	Displays process statistics
Ctrl-U	Discards the current input line and performs carriage return.
Ctrl-W	Refreshes the screen
Ctrl-X	Flushes the type-ahead buffer
Ctrl-Y	Interrupts command or program execution and returns control to the DCL command line interpreter
Ctrl-Z	Indicates end of file for data entered from terminal