Available either as a dealer upgrade to a Model A or straight from Acorn in its Model B variety, the BBC Model B quickly became established as one of the most expandable and versatile computers available.
With an extra 16K, user VIA interface, analogue interface and connectors for all manner of things from discs to 1 MHz devices to second processors, the BBC Model B was the big brother to the Model A.
Even the BBC Model B was a tape-only machine without the addition of a disc upgrade supplied by Acorn. The two key components to this were the Intel 8271 floppy disc controller and Acorn Disc Filing System ROM. The 8271 was later replaced by the Western Digital 1770 series of floppy disc controller. The 1770 came mounted on its own little board to fit into the 8271 socket and 1770 upgrades were produced by Acorn, Watford Electronics and others. The 1770 controller could support higher density disc storage, allowing the Advanced Disc Filing System to be introduced for floppy discs along with an expanded version of DFS.
Other on-board expansion options for the BBC Model B were the Econet system and speech upgrade.
During its production era, the BBC micro underwent a number of minor changes both to the circuitry and the external appearance. A couple of different types of keytops were used in the Model B - the differences can be seen in the "SHIFT" and "TAB" keys as there are wide-spacing and narrow-spacing versions of these keys.
There are "rough" and "smooth" texture versions of the case. Station 128 appears to be a hybrid as the lower case is "smooth" and the lid is "rough" - being an obvious replacement at some point in its long life.
Some BBCs have a completely intact keyboard sticker (the black background surrounding the keyboard) whilst some are perforated where the cartridge ROM system fits.
The most visible difference is the wording on the function key strip. It will say either the original "BBC microcomputer" or the later "British Broadcasting Corporation Microcomputer System". The legend was changed around the time of the introduction of the BBC micro into America, where the "BBC" abbreviation was already in use.
The main circuit board in the BBC micro reached issue 7 although issues 5 and 6 never went into production. The most common types are issues 4 and 7. If you need to perform a disc, Econet or speech upgrade to a BBC Model B it is handy to have an issue 4 or 7 as these motherboards require the fewest modifications.