IBM BASIC

Microsoft BASICA is a simple disk-based BASIC interpreter written by Microsoft for the IBM-PC to be distributed with PC-DOS. The name "BASICA" is short for "Advanced BASIC". The interpreter required the presence of ROM BASIC on the PC's BIOS chip. ROM BASIC is a program which was loaded by the BIOS on early PC's when no disk operating system could be found. BASICA was launched under DOS by the user. Once running it relied heavily on the ROM BASIC interpreter to parse the program source code. BASICA does add some features to the language which the ROM by itself would be be capable of such as filesystem access statements and the ability to save your work at the end of a session. In a technical sence, BASICA is a wrapper for ROM BASIC to allow use of the embedded ROM BASIC interpreter even while an operating system was installed.

The BASICA development envirnment was very similar to the original envirnment used by the original Dartmouth BASIC. The user was given a prompt for entering program instructions. Statements beginning which a line number were inserted into the user's program at the appropriate position so that the statements would execute in numerical order. Statements which did not contain a line number were interpreted immediately. Some commands were intended to be used at run-time (such as LET, INPUT, WHILE and FOR) while other's were intended to be used as design-time (such as SAVE, LOAD, NEW and RUN) but BASICA did not enforce these restrictions.

The following is an example of a session with BASICA:

The IBM Personal Computer Basic Version A2.00 Copyright IBM Corp. 1981, 1982, 1983

Ready.
> list

Ready.
> 10 print "please type your name"

Ready.
> 20 input a$

Ready.
> 30 for t = 1 to 10

Ready.
> 40 print "hello "; a$;

Ready.
> 50 next t

Ready.
> 60 print a$; " you have "; str$(len(a$)); " letters in your name!"

Ready.
> run 
please type you name
john hancock
hello john hancockjohn hancockjohn hancockjohn hancockjohn hancockjohn
hancockjohn hancockjohn hancockjohn hancockjohn hancockjohn hancock yo
u have 12 letters in your name!

Ready.
> system 

A similar BASIC interpreter was Microsoft GW-BASIC except that it shipped with MS-DOS and didn't rely on the embeded ROM BASIC interpreter. Eventually IBM and other PC clone manufacturers removed ROM BASIC from the BIOS to make room on the small chip for more advanced features such as Plug and Play and Advanced power management. In 1983 GW-BASIC was replaced with an even more advanced product from Microsoft called QBASIC or QuickBASIC. While Microsoft sold QuickBASIC seperately from DOS, a subset of the language called QBASIC continued to be included with DOS and later Windows.