How SQL Server Stores MONEY and SMALLMONEY, and the Rounding Trap
money and smallmoney are just integers scaled by 10000. The real page bytes, why the ranges are what they are, and the four-decimal truncation trap that bites calculations.
How SQL Server Stores DECIMAL and NUMERIC, Down to the Bytes
decimal and numeric store a sign byte plus a little-endian integer scaled by the column scale. Why precision buys storage in tiers, and why an oversized decimal is not free.