Peripheral devices installing back door hiding 100 computer commands (9)
I believe the answer is:
microcode
'computer commands' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'peripheral devices installing back door hiding 100' is the wordplay.
'peripheral devices' becomes 'mice' (mouse is a kind of device. I am not sure about the 'peripheral' bit.).
'installing' indicates putting letters inside (inserted letters are installed).
'back' says the letters should be written backwards.
'hiding' is an insertion indicator.
'm00' becomes 'C' (Roman numeral).
'door' enclosing 'c' is 'docor'.
'docor' reversed gives 'rocod'.
'mice' going around 'rocod' is 'MICROCODE'.
Can you help me to learn more?