Editing Commodore 64 (section)

=== BASIC ===
{{Main|Commodore BASIC}}
[[File:Simons Basic Splash Screen.gif|thumb|right|The [[Simons' BASIC]] interpreter start-up screen. Note the altered background and text colors (vs the ordinary C64 blue tones) and the {{nowrap|8 [[kilobyte|KB]]}} reduction of available BASIC-interpreter program memory allocation, due to the [[address space]] used by the cartridge.]]

As is common for home computers of the early 1980s, the C64 comes with a BASIC interpreter, in ROM. KERNAL, I/O, and tape/disk drive operations are accessed via custom BASIC language commands. The disk drive has its own interfacing [[microprocessor]] and ROM (firmware) I/O routines, much like the earlier CBM/PET systems and the Atari 400 and Atari 800. This means that no memory space is dedicated to running a [[disk operating system]], as was the case with earlier systems such as the Apple&nbsp;II and [[TRS-80]].

Commodore BASIC 2.0 is used instead of the more advanced BASIC&nbsp;4.0 from the PET series, since C64 users were not expected to need the disk-oriented enhancements of BASIC&nbsp;4.0. The company did not expect many to buy a disk drive, and using BASIC&nbsp;2.0 simplified VIC-20 owners' transition to the 64.<ref name="heimarck198706">{{cite news|url=https://archive.org/stream/1987-06-computegazette/Compute_Gazette_Issue_48_1987_Jun#page/n21/mode/2up|title=When 2 + 3.5 + 4 = 7 / The Evolution of Commodore BASIC|date=June 1987|work=Compute!'s Gazette|pages=20–26|access-date=June 30, 2014|author=Heimarck, Todd}}</ref> "The choice of BASIC&nbsp;2.0 instead of 4.0 was made with some soul-searching, not just at random. The typical user of a C64 is not expected to need the direct disk commands as much as other extensions, and the amount of memory to be committed to BASIC were to be limited. We chose to leave expansion space for color and sound extensions instead of the disk features. As a result, you will have to handle the disk in the more cumbersome manner of the 'old days'."<ref>{{cite magazine |url=https://archive.org/details/Commodore_The_Microcomputer_Magazine_Volume_03_Number_04_1982-08_Commodore_US/page/n64/mode/1up | title=BASIC Programming on the Commodore 64 | volume=3 |number=4 | magazine=Commodore Magazine |date=August 1982 |page=65 |via=Internet Archive}}</ref>

The version of [[Microsoft BASIC]] is not very comprehensive and does not include specific commands for sound or graphics manipulation, instead requiring users to use the "[[PEEK and POKE]]" commands to access the graphics and sound chip registers directly. To provide extended commands, including graphics and sound, Commodore produced two different cartridge-based extensions to BASIC&nbsp;2.0: [[Simons' BASIC]] and [[Super Expander 64]]. Other languages available for the C64 include [[Pascal (programming language)|Pascal]], [[C (programming language)|C]],<ref>{{cite web|author=ShadowM |url=https://www.lyonlabs.org/commodore/onrequest/powerc/index.html |title=Power C for the Commodore 64 |website=Lyonlabs.org |date=May 2, 2019 |access-date=February 9, 2020}}</ref><ref>{{cite web|url=http://www.clipshop.ca/Aztec/compilers.htm#commodore |title=Wonderfully Ancient Aztec C Compilers |website=Clipshop.ca |date=July 15, 1986 |access-date=March 18, 2017}}</ref> [[Logo (programming language)|Logo]], [[Forth (programming language)|Forth]],<ref>{{cite web |author=Handic Software |title=C64-FORTH  |date=1983 |work=Commodore Info |oclc=19379992 |url=https://www.commodore-info.com/cartridge/item/handic_c64-forth/en/desktop}}</ref> and [[FORTRAN]]. Compilers for BASIC&nbsp;2.0 such as Petspeed&nbsp;2 (from Commodore), Blitz (from Jason Ranheim), and Turbo Lightning (from [[Ocean Software]]) were produced. Most commercial C64 software was written in assembly language, either cross-developed on a larger computer, or directly on the C64 using a machine code monitor or an assembler. This maximized speed and minimized memory use. Some games, particularly adventures, used high-level scripting languages and sometimes mixed BASIC and machine language.