In database access technologies from Microsoft, what is the main difference between RDO (Remote Data Objects) and ADO (ActiveX Data Objects)?

Introduction / Context:
Microsoft has provided several generations of data access technologies for Visual Basic and other environments. Remote Data Objects, or RDO, was an early object model designed mainly for working with ODBC data sources. ActiveX Data Objects, or ADO, was introduced later as a more modern and flexible model built on top of OLE DB. This question asks you to identify the main difference between these two approaches to data access.

Given Data / Assumptions:

• We are comparing RDO and ADO as programming models, not graphical controls.
• RDO was designed to make ODBC access easier for Visual Basic developers.
• ADO was designed to expose OLE DB data providers in a unified way.
• ADO is generally considered the successor to RDO in Microsoft data access strategy.

Concept / Approach:
RDO wraps ODBC API calls in COM objects so that Visual Basic code can call methods such as OpenResultset without working directly with low level functions. It is relatively limited to relational databases with ODBC drivers. ADO, in contrast, uses OLE DB providers under the hood and presents a simpler, recordset based model that can work with relational databases, spreadsheets, and other data sources. ADO is more flexible and was promoted by Microsoft as the preferred data access model for many years after its introduction.

Step-by-Step Solution:
Step 1: Recognize that RDO is older and primarily tied to ODBC, which is a standard for relational database connectivity. Step 2: Recognize that ADO is newer and built on OLE DB, which is a more general interface that supports many kinds of data sources. Step 3: Evaluate option a, which states exactly this distinction, describing RDO as older and ODBC focused, and ADO as newer and OLE DB based. Step 4: Option b incorrectly describes both technologies as unrelated to data access. Step 5: Option c reverses the direction of evolution by saying RDO replaces ADO, which is not historically correct. Step 6: Option d claims they are identical, which ignores clear technical differences. Step 7: Option e mislabels RDO as a browser and ADO as a server, which is completely incorrect.

Verification / Alternative check:
Documentation and migration guides from Microsoft often explain that applications built with DAO or RDO can be upgraded to ADO to take advantage of a more uniform object model across different data sources. This confirms that ADO is intended as a more flexible and modern replacement, while RDO remains limited to ODBC relational connections. The emphasis on OLE DB providers in ADO tutorials further supports the definition in option a.

Why Other Options Are Wrong:
Option b, option d, and option e describe roles that are unrelated to the actual purpose of RDO and ADO. Option c misstates the technology timeline by suggesting that RDO is newer and more complete than ADO, when in reality ADO is the later technology.

Common Pitfalls:
Some developers who inherit legacy applications may confuse DAO, RDO, and ADO because they all involve data access objects with similar names. Another pitfall is to assume that RDO can easily support all data types that ADO can, which is not true. Understanding the difference in underlying technologies (ODBC versus OLE DB) helps clarify which tool is more appropriate for modern applications.

Final Answer:
The main difference is that RDO is an older object model focused on ODBC data sources, while ADO is a newer and more flexible object model built on OLE DB that supports a wider range of data sources.