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MBASIC is the Microsoft BASIC implementation of
BASIC BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
for the
CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...
operating system. MBASIC is a descendant of the original
Altair BASIC Altair BASIC is a discontinued interpreter for the BASIC programming language that ran on the MITS Altair 8800 and subsequent S-100 bus computers. It was Microsoft's first product (as Micro-Soft), distributed by MITS under a contract. Altair BASI ...
interpreters that were among Microsoft's first products. MBASIC was one of the two versions of BASIC bundled with the
Osborne 1 The Osborne 1 is the first commercially successful portable computer, released on April 3, 1981 by Osborne Computer Corporation. It weighs , cost US$1,795, and runs the CP/M 2.2 operating system. It is powered from a wall socket, as it has no on- ...
computer. The name "MBASIC" is derived from the disk file name MBASIC.COM of the BASIC interpreter.


Environment

MBASIC version 5 required a CP/M system with at least 28 kB of
random access memory Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A Random access, random-access memory device allows data items to b ...
(RAM) and at least one diskette drive. Unlike versions of
Microsoft BASIC-80 Microsoft BASIC is the foundation software product of the Microsoft company and evolved into a line of BASIC interpreters and compiler(s) adapted for many different microcomputers. It first appeared in 1975 as Altair BASIC, which was the first v ...
that were customized by home computer manufacturers to use the particular hardware features of the computer, MBASIC relied only on the CP/M operating system calls for all input and output. Only the CP/M console (screen and keyboard), line printer, and disk devices were available. MBASIC in the uncustomized form had no functions for
graphics Graphics () are visual images or designs on some surface, such as a wall, canvas, screen, paper, or stone, to inform, illustrate, or entertain. In contemporary usage, it includes a pictorial representation of data, as in design and manufacture ...
, color, joysticks, mice,
serial communications In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are ...
, networking, sound, or even a real-time clock function. MBASIC did not fully support the features of the host CP/M operating system, for example, it did not support CP/M's user areas for organizing files on a diskette. Since CP/M systems were typically single-user and stand alone, there was no provision for file or record locking, or any form of multitasking. Apart from these limitations, MBASIC was considered at the time to be a powerful and useful implementation of BASIC.


Features


Language system

MBASIC is an interpreter. Program source text was stored in memory in tokenized form, with BASIC keywords replaced by one-byte tokens which saved memory space and speeded execution. Any line prefixed with a line number was stored as program text; BASIC statements not prefixed with a line number were executed immediately as commands. Programs could be listed on the screen for editing, or saved to disk in either a compressed binary format or as plain
ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
text. Every source line was identified with a number, which could be used as the target of a
GOTO GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
or
GOSUB BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
transfer. Only line editing commands were provided.CP/M products providing full-screen editing support required their own installation routines to customize the software for the specific
computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...
used as the system console. No support was provided within CP/M to standardize terminal capabilities.
It was often beneficial to save a program as plain text and edit it with a full featured editor. Program text, variables, disk buffers and the CP/M operating system itself all had to share the 64 kilobyte address space of the 8080 processor. Typically when first starting MBASIC there would be less than 32 kB memory available for programs and data, even on a machine equipped with a full 64 kilobytes of RAM. Comment lines, prefixed with the REM keyword or an apostrophe, could be placed in the program text but took up valuable memory space, which discouraged BASIC users from fully documenting their code. To allow larger and more complex programs to be run, later versions of MBASIC supported functions that allowed portions of program text to be read in and executed under program control (the " CHAIN " and MERGE statements). No support for "shell" command execution was provided, though this functionality could be duplicated by a determined programmer. A particular advantage of MBASIC was the full-text error messages provided for syntax and run-time errors. MBASIC also had a "trace" function that displayed line numbers as they were executed. While this occupied the same screen space as normal program output, it was useful for detecting conditions such as
endless loop , also called Eiko or Peko, is a female J-pop singer-songwriter, and producer who is currently affiliated with Heart Company. She is best known for singing the opening themes of the anime series ''Higurashi When They Cry''. Eiko also handles a s ...
s.


Files and input/output

Data could be read and stored to disk as either sequential files (delimited by the CP/M convention of CR/LF at the end of each line) or else as fixed-record-length random access files, which, given a sufficiently determined programmer, could be used to perform database-type record manipulation. The
Microsoft Binary Format In computing, Microsoft Binary Format (MBF) is a format for floating-point numbers which was used in Microsoft's BASIC language products, including MBASIC, GW-BASIC and QuickBASIC prior to version 4.00. There are two main versions of the format ...
for
floating point In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be ...
numbers was proprietary to the implementation, which meant that data could only be interchanged with other programs using ASCII text representation or else with extensive programming to convert the binary format.


Variables and data types

MBASIC supported the following data types: * 8-bit character data, in strings of length 0 to 255 characters; * 16-bit integers; * 32-bit
floating point In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be ...
(single precision), equivalent to six decimal digits, with a two-digit exponent; * 64-bit floating point (double precision), equivalent to sixteen decimal digits, with a two-digit exponent. String operators included substring selection, concatenation, assignment, and testing for equality. Arrays of the above types were allowed with up to 7 dimensions, but no functions or operators worked on arrays; for example, there was no assignment of arrays. Unlike some other BASIC implementations of the time, MBASIC did not provide support for
matrix Matrix most commonly refers to: * ''The Matrix'' (franchise), an American media franchise ** ''The Matrix'', a 1999 science-fiction action film ** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
operations,
complex number In mathematics, a complex number is an element of a number system that extends the real numbers with a specific element denoted , called the imaginary unit and satisfying the equation i^= -1; every complex number can be expressed in the form ...
s, or a decimal (BCD) data type for financial calculations. All floating point operations were carried out in software since typical CP/M systems did not have floating point hardware. The built-in mathematics functions (sine, cosine, tangent, natural log, exponential, square root) only gave single precision results. A software
pseudorandom number generator A pseudorandom number generator (PRNG), also known as a deterministic random bit generator (DRBG), is an algorithm for generating a sequence of numbers whose properties approximate the properties of sequences of random numbers. The PRNG-generate ...
was provided; this relied on the user to key in a seed number to obtain a sequence of numbers useful for games and some simulations. MBASIC permitted but did not require the LET keyword for assignment statements. Early versions of BASIC on microcomputers were infamous for one- or two-character variable names, which made the meanings of variables difficult to recall in complex programs. MBASIC version 5 allowed identifiers up to 40 characters long, which permitted programmers to give variables readable names.


Program flow control

Program flow control in MBASIC was controlled by IF...THEN...ELSE... conditional tests, WHILE...WEND loops, and GOTO and GOSUB instructions. No CASE statement was available, although an ON...GOTO... (computed GOTO) provided multi-way branches. Subroutines had no parameters and all variables were global. MBASIC did not make
structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection ( if/then/else) and repetition ( ...
mandatory for programmers and it was easy to write
spaghetti code Spaghetti code is a pejorative phrase for unstructured and difficult-to- maintain source code. Spaghetti code can be caused by several factors, such as volatile project requirements, lack of programming style rules, and software engineers with insu ...
.


PEEKs, POKEs, and user functions

No discussion of BASICs on the 8-bit computers of the late '70s and early '80s would be complete without mentioning the importance of the
PEEK and POKE In computing, PEEK and POKE are commands used in some high-level programming languages for accessing the contents of a specific memory cell referenced by its memory address. PEEK gets the byte located at the specified memory address. POKE sets ...
functions for directly reading and writing to memory. Since these systems typically had no
memory protection Memory protection is a way to control memory access rights on a computer, and is a part of most modern instruction set architectures and operating systems. The main purpose of memory protection is to prevent a process from accessing memory that ha ...
, this allowed a programmer to access portions of the operating system, or functions that would not otherwise be available. This also provided opportunities for user programs to hang the system (by accident, usually). For example, a CP/M programmer might use a POKE function to allow BASIC to switch the console device to the serial port, if the system
BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
supported this. For machines with real-time clocks, a set of PEEK instructions might have been used to access the time. For more complex operations, MBASIC allowed user-defined functions that could be called from a BASIC program. These were typically placed in a reserved area of memory, or POKEd into string constants, as a series of machine codes (op codes). MBASIC also provided hardware INP and OUT instructions that read and wrote directly to the 8080 hardware input/output ports. This could be used to control peripheral devices from a BASIC program if the system hardware permitted. Any MBASIC programs that made use of PEEK and POKE, and of
machine code In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a very ...
user functions, were not portable between machines without modifications.


Successors to MBASIC

Besides Microsoft's BASIC-80 for CP/M, a variant of MBASIC was also available as for the ISIS-II operating system. MSX-BASIC is also a well known successor of MBASIC, featuring several extensions specific to the MSX machines. All the functions of CP/M MBASIC were available in the IBM PC disk-based
BASICA The IBM Personal Computer Basic, commonly shortened to IBM BASIC, is a programming language first released by IBM with the IBM Personal Computer, Model 5150 (IBM PC) in 1981. IBM released four different versions of the Microsoft BASIC interpre ...
or
GWBASIC GW-BASIC is a dialect of the BASIC programming language developed by Microsoft from IBM BASICA. Functionally identical to BASICA, its BASIC interpreter is a fully self-contained executable and does not need the Cassette BASIC ROM found in the ori ...
which made migration of programs from CP/M systems to PC-compatibles possible. The tokens used to represent keywords were different, so CP/M programs had to be saved in ASCII source form. Typically screen formatting escape sequences put into the CP/M version would be replaced with the cursor positioning commands found in the PC versions of BASIC, otherwise little rewriting would be needed.


BASCOM

Microsoft sold a CP/M BASIC
compiler In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
(known as BASCOM) which used a similar source language to MBASIC. A program debugged under MBASIC could be compiled with BASCOM. Since program text was no longer in memory and the run-time elements of the compiler were smaller than the interpreter, more memory was available for user data. Speed of real program execution increased about 3 fold. Developers welcomed BASCOM as an alternative to the popular but slow and clumsy
CBASIC CBASIC is a compiled version of the BASIC programming language written for the CP/M operating system by Gordon Eubanks in 1976–1977. It is an enhanced version of BASIC-E. History BASIC-E was Eubank's master's thesis project. It was developed ...
. Unlike CBASIC, BASCOM did not need a
preprocessor In computer science, a preprocessor (or precompiler) is a program that processes its input data to produce output that is used as input in another program. The output is said to be a preprocessed form of the input data, which is often used by so ...
for MBASIC source code so could be debugged interactively. A disadvantage was Microsoft's requirement of a 9% royalty for each compiled copy of a program and $40 for hardware-software combinations. The company also reserved the right to audit developers' financial records. Because authors' typical royalty rates for software was 10-25%, ''
InfoWorld ''InfoWorld'' (abbreviated IW) is an information technology media business. Founded in 1978, it began as a monthly magazine. In 2007, it transitioned to a web-only publication. Its parent company today is International Data Group, and its siste ...
'' in 1980 stated that BASCOM's additional 9% royalty rate "could make software development downright unprofitable", concluding that "Microsoft has the technical solution o CBASIC's flaws but not the economic one".


Importance of MBASIC

MBASIC was an important tool during the era of 8-bit CP/M computers. Skilled users could write routines in MBASIC to automate tasks that in modern-day systems would be performed by powerful application program commands or scripting languages. Exchange of useful MBASIC programs was a common function of computer
users' group A users' group (also user's group or user group) is a type of club focused on the use of a particular technology, usually (but not always) computer-related. Overview Users' groups started in the early days of mainframe computers, as a way to sh ...
s. Keying in long BASIC listings from a magazine article was one way of "bootstrapping" software into a new CP/M system. At least one compiler for a high-level language was written in MBASIC, and many small games and utility programs ranging from a few lines to a few thousand lines of code were written.


Other uses

MBASIC is also the name of a commercial
BASIC BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
compiler for the
Microchip Technology Microchip Technology Inc. is a publicly-listed American corporation that manufactures microcontroller, mixed-signal, analog and Flash-IP integrated circuits. Its products include microcontrollers ( PIC, dsPIC, AVR and SAM), Serial EEPROM ...
PIC microcontroller PIC (usually pronounced as ''"pick"'') is a family of microcontrollers made by Microchip Technology, derived from the PIC1650"PICmicro Family Tree", PIC16F Seminar Presentation originally developed by General Instrument's Microelectronics ...
family developed by Basic Micro, Inc., unrelated to the CP/M interpreter.


References

* Thom Hogan and Mike Iannamico, ''Osborne 1 User's Reference Guide'',(1982) Osborne Computer Corporation * David A. Lien, ''The BASIC Handbook'', 2nd Edition Encyclopedia of the BASIC Computer Language",(1981), Compusoft Publishing * ''BASIC 80 Reference Manual'', Microsoft Corporation, no date {{BASIC CP/M software Discontinued Microsoft BASICs BASIC programming language family Microsoft programming languages