SACD is a specific physical hardware format which uses DSD as its CODEC.
The relationship between SACD discs and DSD files is similar to that between CD discs and WAV files.
You can't actually "copy" a song off a CD, because they're not stored as ordinary files, however, if you RIP the content of an audio CD, with the minimum amount of alteration, you end up with a PCM file, because the format is basically PCM.
Likewise, the content on an SACD disc is stored in the DSD format.
However, even though SACDs can be ripped, it is tricky to do so (mainly because they were designed to be copy protected so do their best to avoid being ripped).
Lately, a bit of a cult has sprung up around DSD as a CODEC or data format.
A few SACD discs are being produced.
A few studios are actually recording content in the DSD format.
Several companies offer downloads in one of the two or three formats that are essentially "DSD".
And several player programs can play the files (including jRiver and Foobar2000).
No special hardware is required to play DSD files.
(SACD discs use DSD at the "DSDx1" sample rate; some file recordings are at higher sample rates... just as PCM files can be recorded at various sample rates.)
The point is that DSD files are simply digital audio files.
As such they can be streamed, downloaded, or recorded on an ordinary data disc.
(This is more likely to be a DVD disc because, at the sample rate and file sizes involved, a CD-R would only hold about thirty minutes of audio.)
NOTES:
1)
There are several different variations of the file format used for DSD content - including DSD and DXD - and not all players can play all of them.
2)
In terms of frequency response, dynamic range, and the actual amount of data they contain, a DSDx1 file, or an SACD disc, is roughly equivalent to a 24/88k PCM file (an audio CD is 16/44.1k).
They are not exactly equivalent; DSD has both benefits and drawbacks when compared to PCM.
The biggest difference between PCM and SACD versions of various music discs is USUALLY the mastering - which is often somewhat different.
(An exact conversion between PCM and DSD is impossible; but, if you make a "direct conversion", and avoid deliberate alterations, they are very difficult to tell apart, and neither is clearly superior.)
Compared to a standard CD, an SACD has a far wider frequency response; however, because the noise floor at very high frequencies is extremely high, VERY aggressive filtering and noise shaping must be used to reduce the excessive HF noise.
3)
In the land of pirated music, you may find "SACD ISO files".
An SACD ISO file is a DISC IMAGE of an SACD.
An SACD ISO can be ripped from an SACD disc (with special hardware and software), or can be "built directly" from digital audio content with the correct software.
Standard computer drives CANNOT READ OR WRITE SACD DISCS - because the format of the HARDWARE is slightly different.
HOWEVER, an ISO image of an SACD disc CAN be successfully written to a DVD-R blank using an ordinary computer drive and ordinary recording software.
SOME universal disc players, and SOME player programs, which can play true SACD disc, will also treat these as "real SACD discs" and play them; some will not (Foobar2000 and jRiver on Windows can play them).
Some programs that can play SACD ISO files are also able to split them into separate DSD tracks (which can then be played on anything that supports playback of DSD files or downloads).
4)
A few processors, including the XMC-1, can play digital audio content in the DSD format directly (some DACs support it in hardware).
Most processors and DACs do not.
According to the license restrictions, DSD audio from SACD discs can only be sent to other devices via a "secure digital connection" (the only type of common connection that meets that requirement is HDMI).
(This is why many "universal players" offer DSD from SACDs via their HDMI output, but most - legal - hardware SACD players without HDMI outputs do not offer a DSD output.)
Most players that can play SACD discs also offer the option of converting it to PCM internally.
(Because of those license restrictions, they are only supposed to send "full quality PCM converted audio" by HDMI - again "because it is a secure connection".)
5)
DSD content can be encapsulated and sent via a USB connection.
The most common way to do this is called DoP (DSD over PCM over USB).
Essentially any computer, and many player programs, can send DoP audio (nothing special is required from the computer hardware); however, in order to play it, your player or DAC must also support it; many do not.
DoP supports various DSD data rates (DSDx1 and DSDx2 are common, although many devices only support the normal data rate; higher rates run into USB data rate limitations).
In theory, DoP could be used via Coax or Optical S/PDIF connections (I've never seen it done, but there may be a few players or DACs out there that allow it).
6)
It is also possible to send DSD audio "directly" over USB.
VERY few devices currently support this... (it requires special drivers and special hardware).
7)
SACD discs can be "pure SACDs" or "Hybrid SACDs".
Some SACDs include copies of the tracks in both Stereo and Surround Sound formats (this is optional).
A Hybrid SACD disc actually includes a true CD version of the content on a separate physical layer of the media.
(When you put it in a CD player, the player simply ignores the SACD portion and plays the "Red Book CD layer".)
THE SACD AND CD LAYERS ON A HYBRID SACD MAY OR MAY NOT BE PRODUCED FROM THE SAME MASTER.
LIKEWISE, THE SACD VERSION OF AN ALBUM THAT IS ALSO RELEASED SEPARATELY ON CD MAY OR MAY NOT BE PRODUCED FROM THE SAME MASTER.
8)
Just for the record....
The DSD format, and the SACD disc standard, were developed by Sony as an "audiophile alternative" to CDs.
The legitimate "benefits" include the ability to include multi-channel audio; and strong copy protection in the disc format.
The format is widely considered to be a commercial failure.
The license required to produce DSD audio is NOT in the public domain (but, as of the last time I looked, Sony will cheerfully grant you a license for free).