Twelve Showbread loaves were placed on the Table each Sabbath, in two rows, six loaves in each row. They remained on the Table for an entire week. After the loaves were removed, they were eaten by the priests on the following Sabbath. A miracle occurred regarding the Showbread loaves - they never became moldy. The Talmud relates that in the days of Simeon the Righteous (the beginning of the Second Temple period) a priest who ate the mere size of an olive (k'zayit) from the Showbread became satiated. After that time, "the modest would refrain" from eating, because there was not enough for all the priests.(Source: Talmud - Yoma 21.)  
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Contents:   Part I,    Part II,    Part III,    Part IV,    Part V,    Part VI,    Part VII