The Commodore CBM B500, was a similar computer to the P500, but for the business market. The VIC-II chip was replaced by a MOS 6545 CRT Controller, capable of 80 columns text. The SID Sound chip was not removed, but the two joystick ports were. Interestingly, the connectors do exist on the motherboard but the ports in the backside of the case have been removed in this model.

The B500 ran Commodore BASIC 4.0, and came in two versions. One version had 128K RAM, with 64kByte for BASIC and 64kByte for storage, and a version with 256kByte of RAM. This version used three banks of 64kByte of RAM for variable storage.

For storage these computers could use external cassette tapes or disk drives.

The Commodore 500 series was introduced in 1982. They are very similar to the CBM 600 series computers, which were launched at about the same time. Memory ranged from 64KByte to 256KByte. There were three models:

• Model 505 - 64KByte RAM (No documentation found about this machine)
• Model P500 - 128KByte RAM for the professional market
• Model B500 (CBM 510) - 128KByte RAM for the Business Market
• Model B500 (CBM 520) - 256KByte RAM for the Business Market

The machines have 24KByte ROM, a IEEE-488 Bus, a dual 8-bit user port, a RS232C communications port. It also has a joystick port, accessible on the motherboard, but there is no hole in the case for it.

The CBM 500 series uses a lot of the same chips that the Commodore 64 uses are used in the 500 series:

• VIC-II video chip - 320x200, 16 colors, 40 column text
• SID 6581 Sound chip - 3 channel sound

The 500 series uses the MOS Technology 6509 CPU which is capable of addressing up to 1MByte of RAM where the C64 uses the MOS 6502 which can only address 64KByte. In the end, the 500 series did not get produced for the American market due to regulatory problems and the fact that the C64 was much cheaper to manufacture.

Features:

• Extended Basic v4.0
• 40x25 video mode in 16 colors (VIC-II)
• 64/128/256 KByte memory
• MOS 6509 CPU, Clocked at 1MHz
• Built in machine language monitor
• 2 joystick ports, user port & cartridge port
• IEEE488 parallel connector, RS232C port

The CBM-II has two incarnations, the P series (P = personal, or, home use) and the B series (B = business use). The B series was available with a built-in monochrome monitor with detached keyboard (hi-profile) but also available as a single unit with built-in keyboard but no monitor (lo-profile). These machines are often referred to as the "Porsche PETs" due to incorrect rumors that the case was designed by Porsche. Though Commodore did initially consult Porsche for a case design, it proved too expensive to produce, so Commodore enlisted designer Ira Velinski to create one based on the original PET prototype

Commodore BASIC was a dialect of Microsoft BASIC, licensed by Commodore in 1977 for use in the PET 2001. It ran from ROM, freeing all RAM for user programs, and provided an immediate programming environment upon power-up. The interpreter was built on the 6502 processor, with tightly coded routines for tokenization, line storage, and execution. This structure allowed BASIC statements to be entered interactively, stored in memory as linked line records, and executed sequentially or via branching constructs. Commodore kept this design across its entire 8-bit product line, from the PET and VIC-20 to the Commodore 64 and beyond, creating a sense of continuity between machines.

Historically, Commodore BASIC differed from many other implementations in its limited feature set relative to machine capabilities. For example, the original PET BASIC lacked dedicated graphics or sound commands, requiring programmers to manipulate memory directly through PEEK and POKE. Even later versions, such as BASIC V2 on the C64, still omitted high-level graphics and sound statements, in contrast with Atari BASIC or BBC BASIC, which provided structured access to system hardware. Only with extended versions such as BASIC 3.5, 4.0, and 7.0 did Commodore add disk commands, string handling improvements, and more advanced features.

When compared to contemporaries, Commodore BASIC was often criticized as being underpowered, but its simplicity made it approachable. BBC BASIC, for example, incorporated structured programming constructs and inline assembler, whereas Commodore’s offering retained the line-numbered, unstructured style of early Microsoft BASIC. Atari BASIC, developed separately, emphasized graphics and sound integration through dedicated keywords. Commodore’s approach forced users to learn the underlying memory map, making them more technically literate about hardware but also raising the entry barrier for certain types of applications.

Despite its limitations, Commodore BASIC achieved massive popularity due to sheer reach. Millions of units shipped with it as the only built-in interface, ensuring every user interacted with it directly. Its ubiquity in schools, homes, and small businesses made it a de facto teaching language for a generation. Moreover, the reliance on PEEK and POKE, while cumbersome, fostered a culture of type-in listings and hardware exploration. This combination of accessibility, wide distribution, and necessity cemented Commodore BASIC’s role as one of the most influential programming environments of the late 1970s and 1980s.

• BASIC 1.0 (PET 2001, 1977)

  Computers: Commodore PET 2001
  Features: Essentially a stock Microsoft BASIC interpreter running in ROM, with support for integer and floating-point arithmetic, strings, arrays, and file operations for tape storage.
  Limitations: No disk commands, no advanced error trapping, and no machine-specific extensions. Designed as a minimal environment to ship the PET quickly.

• BASIC 2.0 (VIC-20, C64, C-MAX, 1981–1982)

  Computers: VIC-20, Commodore 64, Commodore MAX Machine
  Features: Nearly identical to BASIC 1.0 with minor bug fixes, provided the same core Microsoft BASIC functionality.
  Limitations: No disk drive commands, no dedicated graphics or sound statements. Hardware had to be accessed through POKE and PEEK.

• BASIC 3.5 (Commodore 16, C116, Plus/4, 1984)

  Computers: Commodore 16, Commodore 116, Commodore Plus/4
  Features: Added graphics and sound commands (GRAPHIC, CIRCLE, PAINT, SOUND, PLAY), integrated disk commands (DLOAD, DSAVE, DIRECTORY), plus utilities like RENUM and TRON/TROFF.
  Limitations: Still line-number oriented and lacked the structured programming richness of competitors like BBC BASIC.

• BASIC 4.0 (PET/CBM Business Series, 1979+)

  Computers: PET/CBM 4000 and 8000 series
  Features: Expanded disk support with DLOAD, DSAVE, DIRECTORY, COPY, and SCRATCH. Improved error handling suitable for commercial environments.
  Limitations: Focused on business and disk operations, no graphics or sound capabilities because target hardware lacked them.

• BASIC 7.0 (C-128, 1985)

  Computers: Commodore 128
  Features: Added high-level graphics (DRAW, CIRCLE, PAINT) and sound (PLAY, SOUND) commands, advanced disk operations, structured programming constructs like WHILE...WEND, RENUM, and support for memory banking and multi-mode operation.
  Limitations: Despite enhancements, still less sophisticated in structured constructs compared to BBC BASIC or contemporary Pascal-like systems.

• BASIC 10.0 (C-65 prototype, 1990–1991)

  Computers: Commodore 65 (prototype, unreleased commercially)
  Features: Extended support for high-resolution graphics and larger color palettes through VIC-III, up to 8 MB memory addressing, advanced string handling, and structured commands.
  Limitations: Never commercially released, so its practical impact was negligible despite advanced features.

THe MOS Technology 6509 is an enhanced version of the 8-bit 6502 CPU. Using bank switching the 6509 is able to address up to 1MByte of RAM. The 6502 also could do bank-switching, but did so via separate logic circuits, the 6509 had this logic built in. This extra logic made the 6509 difficult to program, and it was mainly used in the Commodore CBM-II line of computers.

Source:WikiPedia - MOS Technology 6509
Source:WikiPedia - MOS Technology 6502