Source code could be entered with a full-screen editor, and limited facilities were provided for rudimentary program debugging.

The entry-level version of the 5150 came with just 16 KB of random-access memory (RAM), which was sufficient to run Cassette BASIC.

Because it used the 32 KB Cassette BASIC ROM,[2] BASIC.COM did not run on even highly compatible PC clones, such as the Compaq Portable.

It adds disk support and some features lacking in Cassette BASIC but does not include the extended sound or graphics functions of BASICA.

By 1986, all new PCs shipped with at least 256k, and DOS versions after 3.00 reduced Disk BASIC to only a small stub that called BASICA.COM for compatibility with batch files.

BASICA will not run on non-IBM computers (even so-called "100% compatible" machines) or later IBM models, because they lack the needed ROM BASIC.

The early versions of BASICA did not support subdirectories, and some graphics commands functioned slightly differently.

BASIC 1.x's PAINT command also made use of the system stack for storage and when filling in complex areas it could produce an OVERFLOW error.

A ROM cartridge version of BASIC was available only on the IBM PCjr, shipped in 1984, and supported the additional graphics modes and sound capabilities possible on that machine.

Conversely, IBM BASICA versions 2.1 and up refused to run if they detected a PCjr, but they could be patched to work around this limitation.

When loaded, a sign-on identification message displays the program version number, and a full-screen text editor starts (see images, right).

Like most other DOS applications, IBM BASIC is a text-mode program and has no features for windows, icons, mouse support, or cut-and-paste editing.