BBC Master MOS 3.20 and 3.50
Its often quoted that 3.50 has compatibility issues, and so 3.20 is the more 'compatible' MOS
Does anyone have any actual examples of this incompatibility ?
BBC Master MOS 3.20 and 3.50
BBC Master MOS 3.20 and 3.50
BBC Bs, Master 128s, Master Compact, and Electrons, and an A3000 with an ARM3 
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BeebMaster
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Re: BBC Master MOS 3.20 and 3.50
In fact Acorn themselves claim it's less than 100% compatible with MOS 3.20 in their user guide:
I may have perpetuated the idea myself in one of my old pages about Station 201, which is my Master 128 (actually Master 512) with MOS 3.50 fitted, but that machine also has some wacky upgrades including an OS overlay board which jiggers about with the system ROM contents and stops the MOS 3.50 Relocator working, plus as it's a Master 512 it also has CPFS fitted which, for reasons known only to Essential Software, they decided to allocate filing system number 5 as default to CPFS, so it conflicts with Econet. Most of the problems I encountered in the early days of using Station 201 stemmed from these features I think rather than any particular incompatibility between MOS 3.20 and 3.50.
I did a picture set showing some of the differences between the two:
https://www.beebmaster.co.uk/8bit/MOS3-50-0.html
As certain things work slightly differently, and some bugs are fixed, I suppose anything which expects MOS 3.20 behaviour or bugs wouldn't be quite compatible with MOS 3.50.
For the last 3 or 4 years, Station 201 has in fact become my workhorse machine so it gets more use than any of the others by quite a margin, and I don't really recall thinking "this doesn't seem to work properly here, I will try a different Master".
I did a picture set showing some of the differences between the two:
https://www.beebmaster.co.uk/8bit/MOS3-50-0.html
As certain things work slightly differently, and some bugs are fixed, I suppose anything which expects MOS 3.20 behaviour or bugs wouldn't be quite compatible with MOS 3.50.
For the last 3 or 4 years, Station 201 has in fact become my workhorse machine so it gets more use than any of the others by quite a margin, and I don't really recall thinking "this doesn't seem to work properly here, I will try a different Master".
