Addendum for OPUS Discovery 2.22  Disassembly.    Roelof Koning 1995/2007.
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A few remarks regarding the disassembly for version.2.2., as found on WOS.

-- About #0000 (Reset): This is an entry point where Opus pages in during a Spectrum Reset. Not the address #0000 is stacked but address #0001 in order to prevent an endless loop. 
-- About #0048 (Key-Int ): This is an entry point where Opus pages in on every interrupt. The fact that the return address is held in Table #0E opens the possibility to extend the Interrupt Routine when a 6116 RAM is present.
-- At #0030 (Look-up) the disassembly says that 'B' holds the 'table-entry', where later the tables concerned are called sub-tables, which they in fact are. The 'table' in which 'B' is used is a sub table from the table of which the number is given in the DEFB. The value in 'A' determines which subtable is chosen.
-- At #1462 : DE is made to hold the default catalogue length, and not the actual catalogue length as this is not copied into the disktable in RAM.
-- At #18E5 is byte 3 given as "extra sectors". In fact it is the starting number for a sequence of sector numbers on a track, only relevant when formatting.
-- At #18E5 is bytes 4-5 are given as "bootblock-1" where it should say 'number of reserved sectors'. 
-- At #18E5 is byte 7 given as 'control register' where it should say 'Command Mask'. All commands for the FDC (WD1770) hold four bits for information concerning hardware related issues. The bits give information about 'head settling delay', 'write compensation', 'spin up sequence' etc., and must be blended into every command code for the FDC. Such command of course goes into the command register. 
-- At #18E5: Byte 9 in the disk information table is unused.
-- At #1C3E : The 'lost-block' is not lost, nor stored in a specially reserved block. 
In fact it is the boot sector stored on the first sector on disk, which is (hard) side 0, 
track 0, sector 0. This 'absolute' sector 0 is not the 'logical' sector 0, as (at least) one sector is 'reserved'. (Offset => 1)
Note that the number 65536 which is suggested  for calculating the block number of the bootsector is just 00000 (zero) in Machine Code. Which indeed is the absolute number of the boot sector...... The whole exercise comes down to subtracting the offset beforehand, so that when DOS adds the offset as usual during the process, the final result is an absolute sector number and not a logical one.