Secret Weapons of Commodore - the 6509s

The 6509s: The P500, B128/256, B500, 600, 700, BX128/256

Lots of thanks to Ullrich von Bassewitz and Andre Fachat who alerted me to various inaccuracies in the original specs, thanks to about a megabyte's worth of E-mail exchanged within a twelve-hour period one fine August day. :-) Also big thank-yous are owed to Hans Franke, who filled in the checkered history of these European denizens, and to Steve Gray for some of their pre-history. As all the 6509 units owe significant portions of their development to each other, it only makes sense to discuss their history in general before getting down to the specific models.

The B/P series of computers, sometimes known as the CBM-II series, were intended to be followups to Commodore's PET series (in the same way that the 264 series were to herald Commodore's new age of home computers). Their first idea, says Hans, was to develop two lines: the B500, as the "B"usiness model, and the P500, as the "P"rivate (?) model. All of the lines were to have from 64K to 256K of memory, in 64K increments (so four models per line), and were to be identical except for the graphics chip (the VIC-II in the P and the CRTC in the B). Three case designs were also initially considered: the LP "Low Profile" model, typewriter style and flat to be used with an external monitor; the HP "High Profile" model with an internal monitor and separated keyboard; and an unnamed third design based on the HP with an internal drive.

Later on, the 192K variant was dumped and Commodore came up with a uniform numbering scheme. Model numbers ending in 05 were to have 64K, model numbers ending in 10 to have 128K, and model numbers ending in 20 to have 256K. The P500, released as a prototype, gave way to the European 'B' 500s (the 256K 520 was never released); the LP series became the 600s, based on the B500s (though there is some evidence to propose that the 600s were actually descendants of the 700s; see that entry); and the HPs became the 700s, also based on the B500s. The internal drive variants of the HP also were released. Of the 05 models, only the 505 materialised (there is no 605 or 705), and only the 600s and higher have 20 models extant.

Eventually, the Grim Computer Reaper caught up. Bugs in the systems' BASIC ROMs were crippling and development was only in mid-stride before the units were pushed out to be manufactured. As the Commodore 64 slowly took off to its legendary status, Commodore dropped the ailing B/P series in favour of their PC compatible line and released the PC-10 instead. As for the PETs themselves, they actually outlasted their intended successors. Commodore continued to sell the SK models, including the 200/8032-SK, 8096-SK and 8296-D, for some time afterwards until sales made them no longer profitable.

Don't cry for the lost 6509s, though. At least one 6509 survived, the D128, though not in its original form, and eventually with a different microprocessor that while less finicky than its predecessor superficially preserved many of the banking and memory management ideas first introduced in the 6509. That machine became the 128.

The P500
Steve Gray's CBM-II Page
Larry Anderson's P500 Page
aka P128, 'C' Series, PET-II (very, very early Commodore literature), C128-40
Introduced Never officially.
Hardware 6509 CPU @ 1MHz, 24K ROM; 128K RAM, expandable to max 256K internal and 704K external. May have been intended to have two 5.25" floppies, detachable keyboard (like the 700s; apparently, this never came to fruition, as pictures of the few existing P500s show them to be very similar to the 600s. IEEE-488 bus, RS232C, dual 8-bit user port.
Graphics and Sound Identical to the 64; 6581 SID; 6569 VIC-II.
Eventual Fate Released as beta models with the 600/B128 but never publicly rolled out. Replaced by the B500/600 series in Europe and the B128 in the States.

The P500 is very similar to the D128 development model, but I'm pretty certain by now after some correspondence that they are not the same computer.

Early Commodore circulars claim the P500 was to have 40K ROM, not 24; Z-80 and 8088 CPUs were to be available as "optional future processors". UCSD Pascal was also another language option. None materialized.

Because of the identical graphics and sound hardware, Commodore was planning to release versions of 64 software rewritten for the 500s. This never came to pass.

There is a drastic difference in availability of these machines on either side of the Atlantic. While European versions turn up from time to time (thus with PAL VIC-IIs), the USA version is vanishingly rare thanks to yet another interesting Commodore bungle. According to Larry Anderson, Commodore released several demo B128/600s and P500s to stores to entice consumers to buy the then-in-development units. These units were not fully operational, and had not been FCC certified in the United States, but dealers sold them anyway to the great ire of the FCC, which proceeded to threaten Commodore with penalties unless Commodore pulled all the units back (with the exception of the units sold or units the stores would not return). However, once Commodore discovered that the 64 was much more popular (not to mention cheaper to manufacture) than the P500, the P500 was pulled from rollout. Rumours persist that the P500s remaining were 'bulldozed' literally -- run over with a bulldozer to turn them into scrap plastic and silicon -- but nevertheless at least one American unit is confirmed to exist, and hopefully a couple of others. On the other hand, European P500s, while hardly common, are much easier to locate. Presumably Commodore learned its lesson from its run-in with the American FCC?

The P500's screen is superficially similar to the SX-64's; it starts up with a white screen and cyan border and the startup message *** commodore basic 128, v4.0 ***.

The same designer who created the sexy PET 200 look probably sculpted the P500's case as well (or perhaps the B500's).


The B (500) Series
Complete Views of the B500 (.jpg, courtesy Hans Franke)
Portrait (29K) | Backplate (16K, with enlargement of rear decal) | Mainboard (100K) | Keyboard Matrix (41K)
Introduced April 1982
Hardware 6509 CPU @ 1MHz, 24K ROM; 128K RAM (in this unit; supposedly ranged from 64K to 256K) expandable to max 256K internal and 704K external. Rumoured intentions to have two 5.25" floppies, detachable keyboard (like the 700s). Apparently, this never came to fruition, as pictures of the few existing 510s show them to be very similar to the 600s. IEEE-488 bus, RS232C, dual 8-bit user port.
Graphics and Sound 6581 SID; 6545 CRTC.
Eventual Fate The B500 was never released, though the later 505 and 510 models were announced in Europe. The 256K 520 never emerged. Not certain how many sold or when it was discontinued. Probably never released in the States. Based on the use of the same part numbers in the B128/600 series, according to Ullrich, the B500 is likely an early name or incarnation of the 600 design.

Unlike the P500, the B500 series were very similar to the 600/B128 series, but kept the joyport (annoyingly, there's no hole on the back for this, though it is fully wired into the board). In all other facets, the B500 series are largely identical with their descendants, the 600s. Based on the fact that even the part numbers are the same, it's just about impossible to tell if a bare motherboard is a B500 or 600 series (as I found out when I ended up with one).

There are supposedly three in the 500 line: the 520 with 256K, the 505 with 64K and the 510 with 128K. The 520 was never announced and the 500 was never released, but some were actually manufactured (Ian Moote's model has a production serial number, which means there must have been at least one run). Hans' system above is probably a prototype like the US P500, further proof coming from the very old chip date codes and the ROMs, which are piggybacked ROM/