Torn about old information unit (8)
I believe the answer is:
roentgen
'unit' is the definition.
(roentgen is a kind of unit)
'torn about old information' is the wordplay.
'torn' becomes 'rent' (rending is a kind of tearing).
'about' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'information' becomes 'gen' (gen is a kind of information).
'rent' enclosing 'o' is 'roent'.
'roent'+'gen'='ROENTGEN'
(Other definitions for roentgen that I've seen before include "Measure of radiation" , "German physicist" , "Pioneer in radiation" , "X-ray discoverer" .)