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From a hardware point of view: SIngle Board
From a software point of view: SIixteen Bit Organiser.
SIBO is the name that now refers to the range of machines from Psion that include:
Of those machines, the Series 3 and the HC can be grouped together as using an older and less capable version of the EPOC (EPOC16) operating system. All the other machines use a later version capable of (among other things) displaying grey as well as black and white. All my software works solely with this later version.
You will note that I mentioned the EPOC operating system in the previous paragraph. These days EPOC is reserved to refer to the newer EPOC32 operating system developed by Symbian for use with the Psion Series 5 and later machines. Before the Series 5, SIBO referred solely to the hardware architecture used by the Series 3, et al, and EPOC referred to the operating system. When the Series 5 was released by Psion, and Symbian was formed to develop the software for it, the decision was made to have EPOC refer only to the new 32-bit version of the operating system, and SIBO was to perform double-duty to refer to the both the hardware architecture and the 16-bit version of the operating system.
So, these days EPOC by itself or (rarely) EPOC32 refers to the new series of computers, and SIBO refers to the older series.
Is SIBO crappy? I don't think so. It's showing it's age - processes are limited to 64k data segments, only 24 processes can be active at once (including the operating system processes of which there are 6), and no more than 512k can be allocated to run those processes.
It is, however, a very good example of client-server programming. If your process has to do anything, it usually has to talk to another operating system process to do it. This includes reading and writing to files, and drawing on the screen. By separating everything into separate processes, and implementing some very good memory protection in hardware, SIBO is able to insulate faulty processes from everything else.
This is very good for software development. I've done some very dodgy things while writing programs, and while my applications have crashed, my handhelds never have! I have never 'locked up' my machine, nor lost any information through a crash (although I have pressed Psion-D once too many times on the odd occasion!).
Most importantly, SIBO implements pre-emptive multi-tasking. This allows all those processes to appear to work simultaneously.