The DCC media itself is mechanically mostly identical to the compact cassette except that it is one sided and has a sliding metal dust protector not dissimilar to the one on a 3.5" floppy. While the media is similar the recorders themselves are electronically very different to a cassette recorder, a DCC recorder is a digital recorder that archives recording and playback via a stationary 20 track lithographed thin film head (i.e.. it's S-DAT, see: S-DAT Recorders), the sound format was initially a 1:4 compressed 16bit format @ 44.1KHz and later a 18bit format at the same sampling rate although all DCC recorders allowed for recording and playback of 48kHz and 32kHz most units did not have A/D or sampling rate converters capable of using those so recording of 48 and 32 kHz was usually only possible via the digital inputs if the original material demanded it. The compression format used is PASC.
Despite having the ability to play back analogue cassettes with remarkable sonic qualities thanks to its lithographed head and having sound quality close to or slightly better than DAT (depending on your objectives and equipment), much better than MD and having a larger dynamic range than both, it did not do well in the market outside of mainland Europe and in 1997 Philips abandoned the format in favour of another one of their other inventions: the Compact Disk Recordable.
Note that the playback sound quality of analogue cassettes on a DCC recorder is much better than what the quoted audio specs for the analogue sections indicate, but they are typically 30Hz to 16kHz with chrome cassettes, less with ferric, this is similar to a quoted spec for a mid to late 70's hi-fi recorder. In actuality the DCC machines are some of the better sounding cassette playback units out there due to the lithographed heads although some users of portable recorders reported problems with the sound quality of analogue playback.
The reason why people rated the sound quality of DCC so highly even in its earlier 16bit incarnation was due to the voicing that Philips had done on PASC codec, the same codec was later sold as a sort of a real-time pro/semi-pro MP2/MP3 codec in a rack and was popular amongst radio stations that were setting up DAB broadcasts since it was just a fraction of the price the broadcast specialists were asking for a Musicam RT codec. When the BBC finally replaced their old Philips semi-pro DCC based codecs with a modern codec in 2009/10 they got more complaints about a drop in sound quality than when they dropped data rates from 256kb to 192kb, in other words the 15+ year old codec was vastly superior in sound and a reminder to people that any algorithm that strips data from an audio signal needs to be voiced, it is not enough to just do the math.
This was not lost on the home recording market and it was the last bastion of DCC users since at the time it was the only digital format available at a reasonable price that sounded good, Mini Disc had problems with its ATRAC system until about 2000 and some people could never get used to the Atrac system even in the 3+ incarnation, something about the psychoacoustic model used by Sony simply did not agree with a small subset of the population. Philips in fact kept manufacturing professional versions of the DCC recorder for some time after the official demise of the format, although these were sold under the Marantz brand. A dance music mastering room I visited in 2008 still had a DCC recorder at hand, saying that they still got the odd mix in the format.
The tape formulations supplied by manufactures was actually from video tape stock rather than cassette stock, i.e. mostly chromium tapes but cobalt doped ferric formulations were also available at the least in the early days of DCC, for archival purposes the ferric formulations have a longer lifetimes despite the lower price, this use of video tape stock explains why metal tape playback is not officially supported in the DCC standard. A few chromium audio cassette formulations are very similar to video tape formulations so that it's theoretically possible to force some audio cassettes to work in a DCC recorder by modifying the enclosure and tape pad (if you need to seriously over-bias a chrome tape to make it sound right on an analogue recorder, chances are that it's video stock), but no audio cassette ferric formulations are similar to the video type ferric formulations that DCC expects.
The 20 track head is needed despite the recorder using only 9 tracks because the heads combine recording and playback functions unlike the heads on a traditional recorder which can only do so by using siamese heads, this gave the company space to implement a azimuth guide that actually works, the missing 2 tracks are used for playback of analogue tapes. The heads were revolutionary when introduced BTW, they used MR technology which even the computer industry did not start to use until years later, it is the use of this technology which allowed the use of S-DAT at such a slow tape speed, the heads were actually so good that Philips could have used only 1:1.8 compression of a 16 bit signal, much better than they thought they could get away with initially.
Auto-reverse is stipulated in the DCC standard so all decks feature it but obviously only needed for analogue playback, due to the 20 tack configuration of the heads there is no need for the head to be turned around when reversed and playing back analogue tapes unlike a normal 4 track head, this means that none of the alignment problems usually associated with auto-reverse machines are present on a DCC deck.
All DCC recorders feature Philips mechanisms and chipsets, most use Philips logic boards and quite a number of them are just Philips players in a drag. This does not mean that they are all the same some of the Martanz branded players for instance, while basically Philips machines have small mods that make them interesting, other makers such as LG Electronics had different user interfaces etc. It is often stated that Matsushita was a co-developer of the DCC technology but in actuality it was all done in-house by Philips, Matsushita/Technics was their launch partner however.