The PCM-D100 is a continuation of Sony's high resolution recorder lineage. The most obvious difference is that PCM-D100, unlike PCM-D1 and PCM-D50 which required Sony's proprietary memory cards, adopts the more standardized SD memory cards. It is head and shoulder above compared to PCM-D50, although still a no match with PCM-D1 in its build quality.
Recording formats include linear PCM (at 192, 176.4, 96, 88.2, 48 and 44.1kHz); DSD (2.8224 MHz) and MP3 (320 and128 kbps). Additional playback support is provided for FLAC, WMA and AAC files.
Good news is that PCM-D100 inherits all the goodness from PCM-D50, including the useful optical input and output, removable battery compartment, a set of great cardioid mics configurable in A-B, X-Y and ORTF, individual gain knob for each channel.
With longer battery life and standard SD memory card support, users who were fond of linking Sound Devices' UsbPre 2 to PCM-D50 via optical connection can benefit much from these improvements. Sony's PCM-D50 and PCM-D100 remain the only options for which above mentioned setup is possible with a portable recording device. Kudos to Sony for keeping the optical input/output on PCM-D100.