Editing IBM Cassette BASIC (section)

== Disk Variants ==

Three different BASIC builds shipped from IBM, layered on top of Cassette BASIC:

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Microsoft BASIC variants on the IBM PC'''
! Name !! Form !! Notes
|-
| Cassette BASIC || ROM (U29-U32) || Cassette I/O only; no disk; no advanced graphics
|-
| Disk BASIC (''BASIC.COM'') || Loaded from PC DOS, calls into ROM || Adds disk I/O on top of Cassette BASIC
|-
| Advanced BASIC (''BASICA.COM'') || Loaded from PC DOS, calls into ROM || Adds CGA graphics, sound, and event trapping
|}

A 5150 booted without any disk drops straight into Cassette BASIC. Disk and Advanced BASIC are not standalone — both rely on the ROM image and will not run on a clone with no Cassette BASIC ROM. This is why GW-BASIC was developed for the clone market: it is a self-contained equivalent that does not need IBM's ROM.