SQL Server Version and Internal Database Version Number

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Checking the sql server installed.

Select @@version

SELECT SERVERPROPERTY('productversion'), SERVERPROPERTY ('productlevel'), SERVERPROPERTY ('edition')

Compatibility Level

The currently available compatibility levels are:
60 = SQL 6.0
65 = SQL 6.5
70 = SQL 7.0
80 = SQL 2000
90 = SQL 2005
100 = SQL 2008

Internal Database Version

The internal database versions for SQL aren't documented in the Books Online.However, thanks to Paul Randal (@PaulRandal) and his Q&A article in TechNet we have the following list:
SQL Server 7.0 databases have version number 515
SQL Server 2000 databases have version number 539
SQL Server 2005 databases have version number 611/612
SQL Server 2008 databases have version number 655

Database information can be viewed by these means:

1. via dbcc
DBCC TRACEON (3604);
GO
DBCC DBINFO
GO
DBCC TRACEOFF (3604);
or
You can also read the page header by using DBCC PAGE: DBCC TRACEON (3604);
GO
DBCC PAGE (ExampleDB, 1, 9, 3);
GO
DBCC TRACEOFF (3604);

2. viaDATABASEPROPERTY() , DATABASEPROPERTYEXfunction
select DATABASEPROPERTY('db','version')

Backup File Information
Backup file information can be viewed by restore command.

restore labelonly from disk=N'db.bak'
restore headeronly from disk=N'db.bak'
restore filelistonly from disk=N'db.bak'