This article is from the Skydiving FAQ, by Barry Brumitt with numerous contributions by others.
Clearly, this is the most Frequently-Asked-Question posed by all
prospective jumpers.
By law (FAA regulations), all intentional parachute jumps must be made
with a single harness, dual parachute system with both a main canopy
*AND* a reserve canopy. In other words, you have a second (or spare)
canopy in case the first one fails to open properly.
However, it must be noted that the technology utilized in today's
sport parachuting equipment is light years ahead of the old military
surplus gear used in the '60s and '70s. The canopies are DRASTICALLY
different from the classic G.I. Joe round parachutes. The materials
are stronger, lighter and last longer, the packing procedures are
simpler, the deployment sequence is much more refined, etc.
The reserve canopies are even more carefully designed and packed. The
reserve parachute must be inspected and repacked every 120 days by an
FAA rated parachute Rigger - even if it has not been used during that
time.
The student's main canopy is always packed either by a rigger or under
a rigger's direct supervision by experienced packers.
There are also additional safety features employed to ensure canopy
deployment such as Automatic Activation Devices (AAD) and Reserve
Static Lines (RSL) which add still more layers of safety.
 
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