sentence: ) -1 = bbc b with new 1.00 + os ( including 1.20 ) 1 = electron 251 = bbc b + 64/128 253 = master 128 245 = compact 160 = archimedes ( arthur os ) ( obsolete ) 161 = archimedes/a3000 ( riscos ) ??? = acorn a5000 acorn archimedes ( risc os ) with the move to the 32 bit arm cpu and the removal of the 16kb limit on the basic code size many new features were added .