The question here, of course, is how long is "long?"
For the most part, we can still play cylinders from c. 1900 using
examples of the original players which have fortuitously survived;
I think there are currently a few cylinder players available, but
they are far from common. With discs, we are more fortunate...but
primarily because there are many collections and collectors, both
private and institutional. However, both of these technologies have
one additional feature...the fact that they contain information,
along with the method uses to store it, is easily discerned visually
and through touch. If some 33rd century archaeologist encounters
a cylinder or a disc, close examination will reveal the varying
grooves as well as how to retrieve the sound held in them.
(whether anyone understands 20th century Earth English by then is,
of course, not a given!)

Now, with magnetic technology, it isn't as simple. If no tape players,
or even the concept of a tape player, has isn't obvious,
without extensive analysis, that the tape (or whatever media) contains
information in the form of varied magnetization (assuming it still
does by then). Our 33rd century Indiana Jones might well discard or
ignore this mysterious ribbon of coated plastic tape, especially
considering how much other non-information-bearing tape had survived!
Magnetic disks are even worse, since you would need both the requisite
hardware and software to retrieve the data.

Finally, digital optical media such as CD's, DVD's and the like. These
will be, if anything, even more inaccessible! It will take submicroscopic
observation to see that there is anything which even MIGHT contain data
(our neo-Indiana may set out to analyze the light patterns they reflect?)!
Even if the existence of pits and non-pits is discovered, and the use of
digital information deduced, the ones and zeros still have to be decoded
by a sophisticated algorithm before any data can be accessed!

As well, 20th century technology depends on the existence of other 20th
century technology to work. Finding an intact computer is useless if there
is no source of 110 volts of alternating current to power it (or knowledge
that is what is needed). Think of the problems for battery-operated hardware
(anybody seen a 135-volt B battery lately?)

One more consideration...will the information (or the instructions, if
those are preserved as well) be intelligible to our far-down-the-road
posterity? We have all sorts of stone objects inscribed in Etruscan...
what we lack is any comprehension of Etruscan, so they might as well
have not survived as it turns out!
Steven C. Barr