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B-series Lo-profile machine The CBM-II page B-series High-profile machine


Welcome to the Commodore CBM-II page! This page contains articles, news, technical information and pictures of what some may claim as the sexiest machines Commodore ever released before their ultimate demise...

The CBM-II line was Commodore's followup to their original PET/CBM machines. Enhancements included extra memory, better screen editor, three-voice sound (SID), RS-232 port, cartridge port, expansion port, and a new keyboard with function keys... all in a sexy new case.

Originally the line was to be split into a Business line (B-series) and a Professional line (P-series). The P-series was ultimately dropped due to the success of the Commodore 64. A few P-series machines were released to dealers and a few were sold before Commodore decided to cancel the series and recall the dealer units. Luckily I managed to aquire one and you can find some pictures below.


In 1981 Commodore started planning a followup to their aging 6502-based PET line. The PET had 32K, a 6845 video controller, and barely any sound. The VIC-20 had just been released and was doing well. The VIC-20 used a 22 Column colour video chip, the VIC-I. MOS Technologies were developing newer chips; A 40 column colour chip called 'VIC-II', and a sound chip called 'SID'. By this time 32K memory just didn't seem enough so they modified the 6502 chip to support more memory (1 Megabyte) and so the 6509 CPU was born. Around the same time IBM entered the PC market using the 16-bit Intel 8088 chip.

Work started on three lines at the time: The new advanced PET line, a game machine, and another secret project. These were to become the CBM-II series, the Max Machine, and the C64 respectively. We know what happened to the C64... The Max machine was released in Japan but never took off. And the CBM-II line would ultimately split into two lines, the B-series and the P-series. The B-series was, once more, split into both High-Profile and Lo-Profile models.

The CBM-II machines were introduced at the Summer 1982 CES show. There was the P500 Professional Computer for US$995, and the B700 Business Computer for US$2,995. Later, at the Winter CES show the B128 was announced for US$1695. The B700 became the BX256 with built-in 8088 coprocessor board and built-in dual drives. In addition two external drives, the SFD-1001 single and 8250LP dual models, and two printers, the 6400 and MPP-136 were announced with styling/colouring to match.

Due to various factors, such as engineering problems and delays, and the popularity of the C64, Commodore could not produce many CBM-II machines. The P500 was cancelled before going into general production; only pre-production machines exist. The BX machines were never released due to problems with the 8088 board. Eventually, in 1983 some machines were released. Shorly after, in 1985 the remaining were liquidated. By 1987 all machines (about 15,000) had been sold and Commodore handed over all information and documentation to the Chicago B User's Group (CBUG). When Commodore went bust some prototype machines, pre-production machines, 8088 boards, and other variations were discovered.

This was not to be the end of the CBM-II. In the labs at Commodore was another machine. This machine started as a merging of the B-series and the P-series, with 6509 CPU and BOTH the VIC-II and CRTC chips for video. The machine was known as the D128 (perhaps "dual" video). However, the machine was not C64 compatible and the C64 was Commodore's greatest success. It was decided that any new machine should be compatible to the C64, and so the machine was re-engineered and became the C128.


Commodore went through many model number changes for the CBM-II line. Products were announced and then changed (see transactor article). The 128/256 naming convention was generally used for the North American markets using the "CBM", "CBMX", "B" or "BX" designations to indicate the case type and the existence of a coprocessor board (X=Extra processor). The 5x0/6x0 convention for the European markets. Some Canadian product sheets also used the European convention. Some models were listed with a "-80" added to the end to indicate 80 column video. The P500 was the only model with 40-column video with colour. In any case the machines are fundamentally the same save for the power supply and NTSC/PAL video setting.

The following are various models and model numbers released. All machines are basically made up of combinations of the following:

PL1 ProfessionalLow color 128K - 510,520,P500, P128, C128-40, PET-II Extremely rare BETA units
BL1 BusinessLow mono 128K - 610, B500,B128, B128-80 Most common model
BL2 BusinessLow mono 256K - 620, B500, B256, B256-80 See spec-sheet
BL1X BusinessLow mono 128K Yes ? Did this exist?
BL2X BusinessLow mono 256K Yes 630 Did this exist?
BH1 BusinessHighmono 128K - 710, B700,CBM128-80 Common. (See below)
BH2 BusinessHighmono 256K - 720, B700/256, CBM256-80 -
BH2D BusinessHighmono 256K - 720D Very rare, Pre-production
BH1X BusinessHighmono 128K Yes CBMX128-80 -
BH2X BusinessHighmono 256K Yes 730, CBMX256-80 Pre-production
BH2XDBusinessHighmono 256K Yes BX700, BX256-80 Pre-production (See spec-sheet)

Note: There are examples of the B500 with 128K and 256K Ram. Click here for the CBM-II section of Bo Zimmerman's canonical list.


CPU 6509 6509 6509
CPU Speed 2 MHz 2 MHz 1 MHz
Internal Memory 128K or 256K 128K or 256K 128K
Max Internal Memory 256K 256K 256K
Max External Memory 704K 704K 704K
Text Mode 80x25 lines text 80x25 lines text 40x25 lines text
Character Size (pixels) 8x14 8x8 8x8
Colours Monochrome Monochrome 16 Colours
Graphics Mode None None Max 320x200
Monitor Integral Green Screen None,5pin DIN None,8-pin DIN
Disk Drives Optional Internal Via IEEE Via IEEE
Sound 3 voices 3 voices 3 voices
Keyboard Separate Integrated Integrated
Joystick Ports None None 2
IEEE,RS-232,User Ports Yes Yes Yes
Cassette Port Yes (*) Yes (*) Yes
Optional 8088 Board YES Not without mod NO
Built-in ROM Language BASIC 4+, MLM BASIC 4+, MLM BASIC 4+
Power LED None Red LED Green LED

* The cassette port is electrically functional but software support was removed in later kernal revisions.


General Ledger Commodore (Info Designs) B010
Accounts Receivable Commodore (Info Designs) B011
Accounts Payable Commodore (Info Designs) B012
Inventory Control Commodore (Info Designs) B013
Payroll Commodore (Info Designs) B014
Order Entry Commodore (Info Designs) B015
SuperScript II Commodore (Precision Software) B030
SuperBase Commodore (Precision Software) B031
Multiplan Microsoft -
MS-DOS 1.25 Microsoft Requires 8088 board
CP/M-86 Digital Research Requires 8088 board
SuperScript III Precision Software -
SuperBase II Precision Software -
SuperOffice Precision Software -
EasyScript Precision Software -
Calc Result Handic Software Cartridge + Disk
Word Result Handic Software Cartridge
700 Assembler/WorkshopJCL Software Cartridge or Disk
Inventory Northwest Music and Computer -
Profi-Text Völkner Cartridge with Cassette to IEC cable

Hardware Add-ons

8088 Board Commodore Board used an AMD 8088 CPU
8088 Board CBUG Version With an NEC V-20 CPU
24K Cartridge GLA Cartridge adds 24K of RAM to Bank 15. Thanks to Ernie Chorny for lending me the cartridge to test.
Here is a hand-drawn schematic and a view of the board.
1 MEG Board ? -
High-Speed Graphics Commodore Germany External Box with video pass-thru
Proxa 7000 Ultra Electronic Board to emulate CBM 8000 series
8250MINI Ultra Electronic Board for SFD-1001 to add second drive (in 720D machines)
IEC interface Ullrich Von Bassewitz New Kernal with IEC interface for cassette port (schematic)


The CBM-II B-series and P-series are very similar architecturally. The main difference between them is the video chip. The B-series uses the 6845 CRT controller just like the older PET models. The P-series has the VIC-II chip as used in the popular C64 (note: the chip was designed separately and both the B and C64 were announced at the same time). Likewise for the SID sound chip. The other main difference is that the B-series is clocked at 2 MHz while the P is only clocked at 1MHz due to the VIC chip.

The CBM-II series is all about memory. The machines use a 6509 processor which is based on the 6502 core. The 6509 adds memory BANKING. Four extra lines are added to the processor giving 16 possible memory BANKs, or 1 megabyte total addressable memory. In the CBM-II series, BANK 15 is called the system BANK. All ROM, IO, and custom chips as well as some RAM, are located here. Banks 0 to 14 can contain RAM. In the P-series BANK 0 is used entirely for video RAM and BANK 1 is for everything else. In the B-series BANK 0 is not used, only BANKS 1 to 4 depending on the model. In order to maximize memory use the B-series had two different BASIC ROMS. Machines with 128K RAM had "BASIC 128" which used BANK 1 for programs, and BANK 2 for variables. Machines with 256K RAM had "BASIC 256" with BANK 1 for programs, BANK 2 for Arrays, BANK 3 for simple variables, and BANK 4 for string variables.

While flexible, in practice this BANK memory scheme is very hard to work with. There is a small amount of memory in BANK 15 which can be used for machine language programs, however if the code is large then the software must reside in one of the other memory banks. This involves setting up very complicated "transfer" routines in order to access ROM routines and custom chips in BANK 15. Perhaps this is a factor for the relatively small software base for the CBM-II line.

The IBM PC was released around the same time and newer "16-bit" processors were being developed. To take advantage of these newer processors the CBM-II line had enhanced expansion cababilities. A second processor could be attached that could "take over" the system and use the 6509 as a slave CPU. Originally Commodore developed an 8088 board that could run a version of MS-DOS and CP/M-86 although due to the complexity of the design these would not be fully working until much later. Plans to include the 8088 board as standard had to be dropped.

The B-series uses the 6845 video chip. This gives the machine an 80 character by 25-line text display much the same as the old PET/CBM 8000 machines. In the low-profile machines when connected to a monochrome monitor the screen looks quite similar due to the 8x8 character matrix. In the High-profile machines, with integrated monitor, an enhanced character set using an 8x14 matrix provides a very crisp video display.

The P-series uses the VIC-II chip giving the P500 the same colour and graphics capabilities as the well-known C64 computer. There is a small amount of memory in BANK 15 for a text screen, however, an entire BANK of 64K is reserved for VIC-II chip to use making it more flexible than the C64. We can only guess what might have been possible if the P-series had actually been released in quantity.

The SID chip provides 3-voice sound capabilities. The SID was a very advanced sound chip for the time, capable of producing some very complex waveforms. In the P-series this works very similarly to the C64 due to the 1MHz clock. In the B-series, the chip is write-only due to the 2MHz CPU, since the SID is a 1MHz chip.

Finally, rounding out the machine is a standard high-speed serial port, expanded keyboard with 10 function keys and numeric keypad, 4 separate cursor keys, and detached keyboard and integral monitor on the high-profile machines. Much of the rest of the machine is similar to the older PET/CBM machines.


Outwardly, the CBM-II machines are probably the sexiest machines Commodore (or any other company) ever produced. The case is nicely rounded and functional, made of solid plastic in a pleasing tan colour. The keyboard is well designed with a nice feel and good layout. It is the first one to depart from the dark black keys of the PET series and first to have 10 function keys, a "00" key, and the first with 4 separate cursor movement keys. In front of the keyboard the case makes a convenient wrist-rest. In the high-profile models the built-in screen has tilt and swivel for easily adjusting for the best viewing angle. The screen is recessed, reducing light and glare from the side and providing a little privacy from prying eyes in a schoolroom environment.

On the back are all ports. The back panel is metal allowing for quick design changes without worrying about changing the plastic case (unlike the C64). There is no power cable sticking out the side like with the VIC-20/C64 and there is finally a real reset button. This also marks the first Commodore to have a true industry-standard serial port accessable on the back.

Inside for the first time again, there is a real switching power supply, not the big bulky transformer of the PETS or brick-like supply of the VIC. The motherboard is complex and packed tightly with plenty of expansion ports. In the B-series the CPU is clocked at 2MHz, making it the fastest of the Commodore 8-bit machines.

Internal Drive Options

At initial announcement there were to be internal drive options for some machines. No production machines actually shipped with internal drives. Later, Commodore did release the CBM8296D machines which used the B-series case and had internal 8250LP drive units.

If you look at the B-series documentation (schematics, memory map, spec sheets) you will see that $1000-1FFF is designated as "Disk ROM" and $D900 is "Disk Units". It's clear that initially the internal drives would NOT be IEEE units. This is proven by the fact that no B-series motherboard has an internal IEEE port (like the CBM8296D does). It is possible that these "Low Cost Disk Units" might be controlled with the internal 6509 CPU. It's also possible that this could also have been the "TCBM" style interface as used in the 1551 drive of the C264/TED series machines (C16, Plus4 etc). Ultimately this was not to be.

Some 720D units with internal drives were discovered in the Commodore labs. These drive units are IEEE drives. Very early units have an SFD-1001 board with an additional daughterboard. This board is labelled 8250MINI. It is not clear if these were made by Commodore as they say "ULTRA ELECTRONIC" on the bottom. It is possible that Commodore planned to offer both internal single and dual drive machines. If you wanted one drive you would get the SFD-1001 board. If you wanted to add a drive later then the daughterboard could be installed. Later 720D machines have an 8250LP installed with modified mounting hardware. In a normal 8250LP the "analog" board is mounted to the main board between the two drives. In the 720D the analog board is connected via ribbon cable, and mounted to the side of the drives, as the power supply is at the top back of the unit. In the CBM8296D the board is mounted behind the drives since the power supply is at the side and bottom.

Michau has successfully installed the internal drive mechanisms from an 8296D machine into his 720 machine. He has written a nice tutorial here. Check it out!

Connecting IEC Drives

The CBM-II line uses IEEE to communicate to external drives. These days, IEEE drives are harder to find and expensive. Serial IEEE (known as IEC) drives are much more common. Almost all new storage solutions, such card-based drives, use the IEC protocol. It would be desirable to be able to connect such devices such as the 1541, 1581, or uIEC to the CBM-II machines. The uIEC in particular will give huge storage capability and easy file transfer from the PC.

Luckily, several solutions exist...

In 2009 I built the cable and tested the both of Ullrichs' solutions. It was my intent to adapt and expand the routines and create a new cartridge solution, unfortunately lack of time prevented me from working on it. Luckily Michau took on the task and has done a great job!

The 8088 Board

The 8088 board is an internal add-on that allows the B-Series machines to run CP/M-86 and MS-DOS. Originally announced along with the B-Series and planned to be factory installed this board was never completed by Commodore. When Commodore handed all information to CBUG, a few members worked to get them running, and finally did. The CPM and MSDOS disks are specially formatted for the Commodore IEEE drives.

The 8088 board is very rare... only 40 were made, and of those, only a dozen or so are known to have survived.

Personal Notes

The CBM-II machines are very cool to me. I think that the machines had a lot of potential. It seems that they suffered from bad timing and/or lack of foresight. IBM were bringing out the "PC" and 16-bit machines were poised to take over. Plus, with the C64 being so popular Commodore couldn't devote enough resources into producing the CBM-II's. Perhaps they were just too complex to get all the bugs worked out or to program.

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B-series Technical Specifications

P-series Technical Specifications

Related Specsheets and Pictures

These are spec sheets I picked up while attending a World Of Commodore Show in Toronto (Malton actually). I loved picking up info sheets at all the shows I went to (and I went to every one I believe). Also included are pics from some of the Commodore catalogs, pictures of the user's guide and even the label from the original shipping box from my B128.


It appears almost 50% of the visitors to this page are searching for the B128 Manual or User Guide. If you are interested in a scanned copy please email me. If there is enough demand I will scan and post it.


A High-Profile B-series machine was seen in the movie "The Jewel of the Nile". When Kathleen Turner's character is in the palace snooping around she discovers an operations room with maps and computers in it. There are 4 high profile machines in the room, two on one desk and two in the background. I frame-by-frame advanced the scene and discovered the machine on the right is a PET-SK and the one on the left is a B, based on the keyboards. In between the two machines are two SFD-1001 disk drives. In the background are two more machines that could be either SK or B but I can't tell. View frame from movie (time index 00:32:30)

The case design was rumoured to have been designed by Porsche. While true that Commodore went to Porsche initially and a case was designed, it would have been prohibitively expensive to produce. Instead, armed with the original PET design they turned to a Boston design firm. Ira Velinski was the man that ended up designing the case, which later won an international award. The case designs were one of the few computer cases Commodore ever patented.

Tips and Tricks

Steve's Pictures

These are my machines. I purchased the B128 from Protecto when they were being liquidated. The B500 I bought later from the same guy that had the B Prototype machine below. The P500 was purchased from ebay. The B128 was my main machine for quite a while. I prefered it over my C64. In fact, the machine was used to run the family business, doing invoices and accounts recievable with custom software I wrote for it. I even upgraded the RAM and built a nice little internal speech-synthesizer module for fun. I ran the unit with my SFD-1001 drive.

I recently picked up another B128 from ebay in 2006, a 710 in 2009, and a European P500 in 2010.


The P500 is a rare machine. I got mine on ebay from a guy in California. Estimates are that only 1500 or so of these machines were produced. The European P500 (pal video) is more common, however on a few North American NTSC machines are known to exist now. I now own one of each. The NTSC version is shown below.

B Family:

Various pictures showing my LP machines together. Ya, I know they look the same but hey it's all about quantity ;-)

B Prototype:

I bought this machine from a developer. It is an early B-series prototype. From Edward Shockley's web pages I understand that this might be the only surviving B prototype. It was hand-assembled in a PET case. All chips are socketed and it has a ceramic 6509 CPU, probably from the first production run. Notice there are no PLA chips, so all the addressing logic is done by discrete chips.

I received this unit in working condition but with keyboard problems, making typing impossible. It appears that there were bugs in the firmware roms (EPROMs on adapters) and I was able to burn replacement Kernal/BASIC ROMs to get the unit operational. I was disappointed to find that the machine is missing the small 4K ram in Bank 15 where I normally code my ML routines.


This machine was purchased from a kind gentleman who saw this web page. I always wanted a High-profile machine and this one is in mint condition. I always thought the machines were bigger but they are relatively small and light. It is working but seems to have no sound output.

Other Picture Submissions

These pictures have been submitted by other CBM-II owners. Thanks!

I'm looking for pictures of any High-profile machine with internal drives, and any hardware addons. Contact me if you can contribute some pictures!


Request for Info

I am looking for information on the following:

I am looking to document the different models of the CBM-II line. Commodore announced many different model numbers, but which ones are "real". And, how many were made? If you have a picture of the serial number label from your machine please email it to me. I am particularly interested in labesl for CBM256-80, 710, 720, 710D, 720D, P500. Does anyones machine have an actual label that says P128, 505, 510,520, or C128-40?


I also collect Commodore machines. Check out Steve J. Gray's Commodore Collection page.

I would like to add to my collection of CBM-II and other Commodore equipment... I am looking to purchase the following equipment. If you have anything on the list you would like to sell please contact me!


Last updated: Jan 6/2011, 10:40am EST

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