The 1MB ROM isn’t the largest it’s been, traditionally parts of the (classic) Mac OS had been in ROM, and by the PowerPC era it was up to 4MB. The first iMac wa

The 1MB ROM isn’t the largest it’s been, traditionally parts of the (classic) Mac OS had been in ROM, and by the PowerPC era it was up to 4MB. The first iMac was the first Mac to move the OS parts out of ROM and into a file loaded from disk into RAM. 1MB is still bigger than PC, but it was more sophisticated with the Forth stuff, network booting (which would be an extra option ROM on the PC) etc. In the case of ADPCM, there’s probably a trade off between size of the sound data vs the size / complexity of the decompression algorithm itself. Nothing apart from the startup sound probably uses the decoder (especially as the chimes of death / car crash noises were replaced with beeps from the iMac onwards) so the whole thing probably has to be counted together.