What is SAP?
SAP stands for Systems Applications and Products.
In 1973 the SAP R/1 solution was launched. Six years later, in 1979, SAP launched SAP R/2. In 1981, SAP brought a re-designed product to market. However, SAP R/2 did not improve until the period between 1985 and 1990. SAP developed and released several versions of R/3 in 1992 through 1995 which were like 3.0, 3.6c, 4.0, 4.6c and then ECC6.0 (ERP Central Component).
SAP r/3 which means System Application Products in 3 tier Architecture. 
Here 3 tier refers to the 3 layers- Database layer , Application Layer and Presentation Layer. In this type of model there should be one database layer, at least one Application layer and one or more presentation layer( for SAP its SAP gui SAP logo).
SAP stands at #1 in the ERP market with more than 1,40,000 installations worldwide and over 25 industry-specific business solutions with its roots growing in more than 120 countries.
ADVANTAGES :
- SAP is platform independent that means it can run on any Windows NT/ Windows XP, IBM-AIX, SUN-Solaris, Tru64-Unix and HP-UX. OS/390, ZLinux and Microsoft .NE and others.
- SAP is also database independent support ORACLE, MSSQL and others.
- SAP is language independent like EN for English, Japanese, German.
- SAP is support multiple currencies.
DISADVANTAGES :
- Need skilled manpower .
- Project implementation cost is high
- Not very user friendly
