How are the "money" and "decimal" data types in SQL Server stored in memory?

Question

I want to know about the storage SQL Server data types in memory.

How is the money data type in SQL Server stored in memory? I know that money is stored in 8 bytes and smallmoney is stored in 4 bytes. But I don't know how?

For example when you have 123400.93 for the money, how is it stored in 8 bytes?

I have the same question about the decimal and DATE data types.

Especially for DATE, the format is YYYY-MM-DD, but how is it stored in 3 bytes? Is it stored as described here: http://dev.mysql.com/doc/internals/en/date-and-time-data-type-representation.html or the number of days from a specific day is stored?

Answer 1

Just adding a bit here...

A single byte is made up of 8 bits. A bit can hold 2 values (0 or 1).

So 4 bytes is 32 bits (4 x 8). Which means the numeric range of what can be stored is from 0 to 2^32 which gives a total range of 4,294,967,296 values.

smallmoney is signed so we drop one of the bits to be used for the sign, which leaves 2^31, or 2,147,483,648 possible values and the +/- sign.

Now we take into account that the last 4 digits of a money type are always after the decimal point and we end up with a range of -214,748.3648 to 214,748.3647

Technically, money and smallmoney values are stored by flipping bits in a word or byte just like everything else. If you need more info, read http://computer.howstuffworks.com/bytes.htm

Or you might see this for the possible value range of money and smallmoney: http://technet.microsoft.com/en-us/library/ms179882.aspx

update
For the DATETIME data type, it's the same concept with a little twist. In MS SQL a DATETIME is stored using 2 numbers. The first is number of days since 1/1/1900 and the second is number of ticks since midnight: See http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/how-are-dates-stored-in-sql-server and When storing a datetime in sql server (datetime type), what format does it store it in?