Question: There are a lot of retro-computers with BASIC as an integral part of the operating system. The IBM 5100 was one of the first computers with a separate memory space for BASIC, followed by the Commodore PET, Apple II and TRS-80.

But why was BASIC built into their operating systems, using memory? From [this memory map](http://sta.c64.org/cbm64mem.html), the Commodore 64 had memory completely reserved for BASIC. There were computers, like the Altair 8800, that provided BASIC as software that could be loaded into memory when necessary, and these computers both worked and sold well.

So why was BASIC built into so many computers' operating systems?

Answer: 
Having a programming language built-in gave you a multi-purpose tool into your hands at the flick of a switch (power on).

As to the choice of BASIC vs. other programming languages, microcomputer BASIC dialects are - despite some of their shortcomings - quite accessible to novice programmers. They are a bit like using English in an imperative style ("PRINT this", "DO that"), so not hard to learn. There was a lot of BASIC literature around at that time and sufficiently general example programs could be ported to different systems without too much work. Many other languages are more cryptic to someone not used to it.

As they were usually included on the ROM chips, they didn't take away any RAM if you chose not to use BASIC.
Having BASIC available for the machine was a selling point so early adopters wouldn't have to wait for software to become available--they could write what they need themselves, and they wouldn't need to learn machine language to do it.

> 
> [Bill] Gates [believed](https://en.wikipedia.org/wiki/Altair_BASIC#Origin_and_development) that, by providing a BASIC interpreter for
>  the new [MITS Altair] computer, they could make it more attractive to
>  hobbyists.
> 
> 
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