IBM supplied two assemblers for the Model 3020: the Model 20 Basic Assembler, and the Model 20 DPS/TPS Assembler. Both supported only instructions available on the Model 20, including unique instructions <code>CIO</code>, <code>TIO</code>, <code>XIOB</code>, <code>SPSW</code>, <code>BAS</code>, <code>BASR</code>, and <code>HPR</code>.<ref name="M20">{{cite book |last1=IBM Corporation |title=IBM System/360 Model 20 Disk and Tape Programming Systems Assembler Language |date=April 1970 |url=https://bitsavers.org/pdf/ibm/360/model20/GC24-9002-5_360-20asm_Apr70.pdf |access-date=October 2, 2023}}</ref>{{rp|page=110}} The Basic Assembler is a slightly more restricted version of System/360 Basic Assembler;<ref name="M20CPS">{{cite book |last1=IBM Corporation |title=IBM System/360 Model 20 Card Programming Support Basic Assembler Language |date=May 1969 |url=http://bitsavers.org/pdf/ibm/360/model20/GC26-3602-5_360_20_Card_Programming_Support_Basic_Assembler_Language_Jan71.pdf |access-date=October 2, 2023}}</ref> notably, symbols are restricted to four characters in length. This version is capable of running on a system with 4 KB memory, and macro support is limited to [[IOCS]] macros. The card versions are two-pass assemblers that only support card input/output. The tape-resident versions are one-pass, using [[magnetic tape]] for intermediate storage. Programs assembled with the CPS Assembler can address a maximum of 16 KB.<ref name=M20CPS />{{rp|pages=7-8}}
The DPS/TPS assembler is a somewhat restricted version of System/360 BPS/BOS Assembler.<ref name=M20 />{{rp|pages=132–134}}
