Microsoft BASICA interpreter

Microsoft BASICA (short for "Advanced BASIC") is a simple disk-based BASIC interpreter written by Microsoft for PC-DOS. BASICA allows use of the ROM-resident BASIC on the PC while DOS is loaded (the ROM BASIC itself runs when nothing is loaded when booting) and adds functionality such as file access and storage of programs on disk.

Lineage

BASICA's development environment is very similar to that of Dartmouth BASIC. In both, a user enters instructions at a prompt. If an instruction begins with a line number (used to sequence the instructions and as a label), it is stored as part of the current program. If not, it is executed immediately.

BASICA's successor is Microsoft GW-BASIC, which is very similar but doesn't use any ROM-based BASIC routines.

Example session

The IBM Personal Computer Basic Version A2.00 Copyright IBM Corp. 1981, 1982, 1983
Ready.
> 10 PRINT "Name: ";
Ready.
> 20 INPUT A$
Ready.
> 30 PRINT A$; ", you have"; LEN(A$); " letters in your name !"
Ready.
> RUN 
Name: John
John, you have 4 letters in your name !
Ready.
>