dynamically while the system is running by a system's manager (i.e.: it is not permanent like a disk file). When logged in, a user can "SWITCH" to any of these environments, type language statements in the BASIC-PLUS programming language, issue RUN commands to specific programs, or issue a special command called a CCL to execute a program with command options. Most RSTS systems managers generated the kernel to include the "Control-T" one line status option which could tell the user what program they were running, under what RTS the program was using, how much memory the program was taking, how much it could expand to, and how much memory the RTS was using. BASIC-PLUS Programs written in BASIC-PLUS ran under the BASIC RTS, which allowed them up to 32K bytes of memory (out of 64K total). The language was interpreted, each different keyword being internally converted to a unique byte code and the variables and data being indexed and stored separately within the memory space. The internal byte-code format was known as PCODE. When the interactive SAVE command was issued, the BASIC Plus RTS simply saved the working memory area to a disk file with a ".BAC" extension. Although this format was undocumented, two Electronic Engineering undergraduates from Southampton University in the UK (Nick de Smith and David Garrod) developed a decompiler that could reverse engineer BAC files into their original BASIC-Plus source, complete with original line numbers and variable names (both subsequently worked for DEC). The rest of the memory was used by the BASIC RTS itself. If one wrote programs in a language that permitted true binary executables such as BASIC-Plus-2, FORTRAN-IV, or Macro Assembler, then the amount of memory available would be 56K (8K allocated to the RTS). The standard BASIC-PLUS prompt is the "Ready" response, pressing Control-T displays status (example): DCL (Digital Command Language) Starting with Version 9, DCL became the primary startup RTS even though it does not have the ability to execute binary programs. This became possible with the advent of the disappearing RSX RTS (see below). DCL was incorporated into all of the recent versions of DEC's operating systems (RSX-11, RT-11, VMS, and later OpenVMS) for compatibility. The standard DCL prompt is the dollar "$" sign (example): $ write 0 "Hello World, it is "+F$TIME() Hello World, it is 01-Jan-08 10:20 PM $ inquire p1 "Press Control-T for 1 line status:" Press Control-T