Specifications (Model A To Model B+128)
| Model A | Model B | Model B+64 | Model B+128 | |
|---|---|---|---|---|
| Processor | MOS Technology 6502A at 2 MHz | Rockwell Semiconductor 6512A at 2 MHz | ||
| RAM | 16 kB | 32 kB | 64 kB composed of 32 kB standard memory, 20 kB video (Shadow) memory and 12 kB extended (special Sideways) memory. | 128 kB composed of 32 kB standard memory, 20 kB video (Shadow) memory and 76 kB extended (Sideways) memory. |
| ROM | 32 kB of ROM composed of a 16 kB MOS (Machine Operating System) chip, and 16 kB read-only paged space defaulting to the BBC BASIC chip. Four paged 16 kB ROM sockets standard, expandable to 16. | 48 kB of ROM composed of 16 kB MOS, 16 kB DFS, and 16 kB read-only paged space defaulting to the BBC BASIC. | ||
| Keyboard | Full-travel keyboard with a top row of ten red-orange function keys ƒ0–ƒ9. These generated text semigraphics when pressed with CTRL or SHIFT, and could be programmed with keyboard macros. The arrow keys and BREAK could also serve as function keys. Links on the keyboard PCB allowed users to select the behavior of Shift+Break, and Display Mode on Power-up/Break. | |||
| Display | As Model B except RGB (Optional upgrade, soldering required). | 6-pin DIN digital RGB connector +5 V/0 V, 1 V p-p composite colour or monochrome video (link S39) and built-in UHF (PAL) RF modulator. | ||
| Graphics | As Model B, but Modes 0, 1, 2, and 3 not available due to lack of memory. | Configurable graphics in Modes 0–6 (see table below) based on the Motorola 6845 CRT controller or Mode 7, a special Teletext mode, based a Mullard SAA5050 Teletext chip and only taking 1 kB of RAM. | ||
| Sound | Four independent sound channels (one noise and three melodic) using the Texas Instruments SN76489 sound chip. Phoneme-based speech synthesis using the Texas Instruments TMS5220 with a custom Acorn ROM (the "PHROM", a TMS6100) of Kenneth Kendall's voice (optional). | |||
| Tape storage | Tape interface (with a relay operated motor control, controlled via 2 pins on a circular 7-pin DIN connector), using the CUTS variation of the Kansas City standard data encoding scheme operating at 1200 or 300 baud. | |||
| Disk storage | Optional floppy disk interface based initially on the Intel 8271 controller and later on the WD1770, also requiring the installation of the DFS (disk filing system) ROM (and of soldered connector on Model A). (5.25" floppy drive usually used) - Densities: Single-Sided, Single Density, Single-Sided, Double-Density, Double-Sided, Single-Density and Double-Sided, Double-Density. | floppy disk controller based on the Western Digital WD1770 controller and DFS ROM as standard (except ANB51, ANB52). | ||
| Hard-disk storage | None (lack of memory). | Additional ADFS ROM required, external drive unit connected to the 1 MHz Bus interface. (Winchester Hard disc drives with 5 MB, 10 MB or 20 MB capacities. Maximum of 512 MB per drive, up to four drives). | ||
| Serial Interface | Optional upgrade, soldering required. | 5-pin 'domino'-DIN RS-423 serial port. | ||
| Parallel interface | Optional upgrade, soldering required. | 26-pin IDC Centronics-compatible parallel port. | ||
| User port | Optional upgrade, soldering required. | 20-pin IDC "user port" with 8 general purpose digital I/O pins and two special/trigger sensitive digital pins used for control purposes (for e.g. a turtle when using the Logo programming language). | ||
| Analogue interface | Optional upgrade, soldering required. | DA15 socket with four 8/12 bit analogue inputs based on µPD7002 IC (suitable for two joysticks), two inputs suitable for pushbuttons and an input for a light pen. | ||
| 1 MHz Bus | Optional upgrade, soldering required. | 34-pin IDC connector for generic expansion on a "daisy-chain" (used for connecting hard disks, sound synthesisers etc.). | ||
| The Tube | Optional upgrade, soldering required. | 40-pin IDC connector for external second CPU. Options included a second 6502, a Zilog Z80, the ARM Evaluation System, or a National Semiconductor 32016 (the latter was either branded "BBC Microcomputer System – 32016 Second Processor" or "Acorn Computer – Cambridge Co-Processor"), other vendors added 6809, 6800, 68000 and 68008. A 10 MHz 80186 co-processor from a BBC Master can be connected through a co-processor adapter to a BBC Micro, thus enjoying a limited degree of PC compatibility. | ||
| Network (Optional extra) | Econet large-scale low-cost networking system – around 100 kbit/s using the Motorola 68B54 (standard on US model). | |||
| Secondary power output | Power supply for external disk drives, 6-pin, top to bottom, left to right: 0V, 0V +5V DC @1.25A, +12V DC @1.25A, NC, -5V DC @75mA, |
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