after shutting down the computer do the ram loses what it remember ? if yes is there some technics that are used to get what is stocked into the ram after shutting down the computer ?
yes RAM chips remember things only while a computer is powered on, so they're used for storing whatever a computer is working on in the very short term.
In today's technology, random-access memory takes the form of integrated circuits. RAM is normally associated with volatile types of memory (such as DRAM modules), where stored information is lost if power is removed, although non-volatile RAM has also been developed.  Other types of non-volatile memories exist that allow random access for read operations, but either do not allow write operations or have other kinds of limitations on them. These include most types of ROM and a type of flash memory called NOR-Flash.
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The main bulk of DRAM is made up of capacitors storing a charge to store the bit. This needs to be refreshed regularly otherwise the capacitor will lose charge due to parasitic drain and electromagnetic effects from accessing neighbouring rows.
When the power is cut the DRAM controller will no longer be refreshing rows so eventually all the capacitors will drain. If you cool the ram module down this will take longer. This property is used in the cold boot attack