maximal size of TRD image

[boo_boo]

are you speaking about maximum capacity that TRD file format can provide?
yes, it may hold that much data, but this is incompatible with any ZX/TR-DOS emulators, since most capacious media supported by TR-DOS hardware/software is DS/DD floppies (standard capacity: 80tracks x 2sides x 16sectors x 256bytes = 640kB, max capacity: 86tracks x 2sides x 16sectors x 256bytes = 688kB)