The registered version removes the time limit and comes with a hardware adapter to connect a Commodore 1541 disk drive to the Amiga's parallel port.
A64 has some extras that a real Commodore 64 is inherently unable to provide.
The most useful of these is an integrated MOS 6510 machine language monitor, which can be invoked at any time during the emulation.
While in the monitor, the emulated Commodore 64 is frozen in place, giving the user full reign over its internal memory and registers.
The emulator also allows machine language program input through 6510 mnemonic codes, rather than raw numeric values.