The Acorn BBC series comprises of several sets of machines which share a similar OS and similar hardware (all 6502 based). The range is as follows:
- Acorn Atom, the original machine with a slightly older OS
- Acorn BBC Micro A, a 16K original machine
- Acorn BBC Micro B, the 32K classic
- Acorn BBC Micro B+, basically a B with 128K of memory
- Acorn Electron, a cut down version of the BBC B, with slower CPU, updated OS, but better hardware support
- Acorn BBC Master, a 512K version of the B with better hardware support and an updated OS
All Acorn systems may support different file systems:
- Tape, built into the OS and doesn't take up much memory
- Disc (DFS), originally this required working memory, which was reduced free memory by nearly 3K; on the Electron and Master, separate memory was included with the disc hardware to allow full access to the memory with DFS.
- Disc (ADFS), an upgrade to DFS that allowed multiple directories, much like modern filing systems. This used up a lot of free memory on the Electron and BBC.
Most images found out there are usually DFS formated discs, these will generally have the extension .ssd or .dsd (Single Sided Disc or Double Sided Disc) and comprise of an exact image of the disc. It is usually best to use a Master or Electron with DFS as you get more free memory.
To use these within an emulator, several OS commands can be used, these are normally referred to as star commands, as they all start with a *. The important ones are:
- *CAT (or *.), catalogues a disc.
- *DISC, selects the DFS filing system
- *DRIVE, selects which drive to use. The drive numbering systems starts with 0, being the first disc drive, 2 is the other side of the first disc drive. 1 is the second disc drive, with 3 being the other side of that disc.
- *TAPE, selects the tape filing system
- *ADFS, selects the ADFS filing system
- *EX, shows extended information about files
- *DIR, changes directory
The Break key (usually mapped to either F10 or Break on a PC keyboard) is special on the Acorn OS, this sends a reset request to the OS, it can be used in several ways:
- Break is used for a soft reset of the system.
- Ctrl + Break is used for a hard reset of the system.
- Shift + Break is used to boot off a device, here the active filing system looks for a file called !BOOT on the disc/tape and loads it.