The Business Operating System, or BOS, is an early cross-platform operating system originally produced for Intel 8080 and Motorola 6800 computers, subsequently for Zilog Z80-based computers, and then later for most microcomputers of the 1980s. 

Have used it on Pinnacle (p-system, 68000), Apricot, Amstrad and others.

CAP Ltd, a British company and at the time one of the world's largest Information Technology consulting firms, developed BOS. CAP designed BOS and BOS applications for platform-independence.

Via a management buyout (MBO) in 1981, BOS was spun off to three interlinked companies, MPSL (MicroProducts Software Ltd) which looked after the sales and marketing of BOS, MPPL (MicroProducts Programming Ltd) which looked after both the development of BOS and various horizontal software packages, and MicroProducts Training Ltd.

The small BOS dealer/distributor network and its command line interface structure met its demise when graphical user interface operating systems became prevalent.

MPSL developed numerous products for BOS, generally targeting the horizontal markets, leaving the vertical markets (i.e. niche) to independent software vendors ISV. Examples of MPSL developed software include BOS/Finder (database), BOS/Planner (spreadsheet), BOS/Writer (word processor) and BOS/AutoClerk (report generation). Companies sold various BOS accounting software suites in the UK and United States. In the UK, BOS accounting packages were considered to be the industry standard by some accountants.

BOS applications were compiled to a p-code and interpreted as they ran. BOS had a p-code interpreter so efficient that programs, even the BOS/Writer word processor, ran sufficiently fast to satisfy users. Apart from a 2-kilobyte (Kb) server (computing)/host kernel, BOS is written in BOS/MicroCobol, a language based on COBOL but with system level programming constructs added and elements of structured programming, which bore a vague similarity to Pascal. In recent computing, programming languages such as Java have re-introduced the concept of p-code "virtual machines".

‘Patches’ to fix issues could be literally that, you were sent a list of four character codes which were then typed into a special editor in a column.  This p-code then replaced the original code in the program to fix the problem.  The code was of course platform independent as it was interpreted at run time, so you only installed a small operating system specific for each platform and then re-used the same application program disc to install on all platforms.

BOS required 48 Kb of RAM and two 250 Kb floppies, though it was more commonly deployed on machines equipped with 64 kilobytes of RAM and a hard drive. A computer with 128 KB RAM and a 10-megabyte (Mb) hard drive could run as many as five concurrent users. When the IBM PC XT came out in 1983, BOS served over eight concurrent dumb terminals on it.

Networking between machines running the OS was built in and a user could have several concurrent screens running as well as it supporting concurrent individual users.

One feature of the Microcobol applications was the ability to access another users screen and underlying program state if their program crashed.  I once called a vendors help line and was able to bring up the users variable list from another screen.  A date had not been initialised and it was possible to set the variable value and restart the program at the point it had stopped, so data or results were lost.

At the time, all these features were quite advanced and made BOS very attractive.