Sequential writing in the file is not used, it is too difficult and it makes no sense.
Writing and reading directly from RAM, blocks of 256 bytes. An temporary buffer is not used.
Yes, I forgot an important question. Do you have any ideas where I could safely place my new disk routines in the memory??? Is there any free RAM which I can use?
The only section of memory to accommodate its own procedures is the area of system variables TR-DOS (#5CB6-#5D22), but must ZXASM completely separated from the TR-DOS calls.
The answers to many questions can find in this book http://trd.speccy.cz/book/TRDOSUA.ZIP. I think it's not a problem to translate it into English.