Last weekend, the interns had a very interesting and energetic seminar with Boss Dinh Manh Dat. With his extensive experience, Mr. Dat provided a profound perspective by comparing old .NET (4.8 and earlier) and new .NET (.NET Core 2016 to present).
In particular, he emphasized the message: "At this point, if any business is still stubbornly using old .NET, it is truly a disaster in terms of technology, operations, and security."
Below is a summary of the core arguments and in-depth analysis from Mr. Dat's sharing for you to “note down”:
Completely different program architecture and performance
Around 2014-2015, the explosion of SPA - Single Page Application technologies like React, Angular, Vue… completely changed web design thinking. Meanwhile, old .NET was still heavily influenced by the traditional ASP.NET era (Web Forms, early MVC) with its heavy server-side rendering mechanism.
Microsoft had to tear down and rebuild new .NET following the SPA model in 2016. It eliminated cumbersome organizations, replacing them with built-in Dependency Injection architecture, streamlined Middleware, and optimized Compile mechanisms. This streamlining helps new .NET applications consume very few resources while achieving superior execution speed.
There's a funny saying that only those who are “hugging” old code (referring to .NET, PHP, JSP… from 10 years ago) still think their web “runs fast” - the rest of the world no longer accepts their page load or response speeds - because nowadays everyone is used to the super-fast response speed of SPA. Do you remember how smooth, fast, and sharp your iPhone 4S was when you first bought it? - Now why does it feel so bad to hold? The reason is that human experience is becoming more refined and demanding.
Old .NET programs contain too much "junk"
To try and achieve a smooth experience with no page reloads, old .NET systems were forced to "stuff" tons of patched-up libraries.
The system was fragmented by cumbersome Ajax code snippets, JQuery, UpdatePanel… and a host of chaotic JavaScript written on top of each other. The result was a huge pile of "junk," making the source code extremely messy and difficult to maintain, while the user experience remained very "clunky" and slow compared to the pure API architecture of new .NET.
EF Core - A leap forward in Data Access
In old .NET, developers were tortured by thousands of lines of "handcrafted" ADO.NET code, or had to endure the extremely slow and heavy SQL string generation mechanism of EF6. Every time the DB configuration was updated, the system was prone to conflicts.
EF Core - Entity Framework Core is the most advanced weapon of new .NET. EF Core boasts query compilation speed from LINQ to SQL that is nearly as fast as native code. In particular, new exclusive features like Compiled Queries, DbContext Pooling - super-fast connection reuse, and Batch Update/Delete - ExecuteUpdate, ExecuteDelete running directly on the DB without loading data into RAM… have completely dispelled the prejudice that "using ORM is slow."
A "ticking time bomb" of security on old Windows Server
An inevitable consequence of using old .NET is being tied to older Windows Server versions, unable to update to the latest - faster and more secure - operating systems in a timely manner.
Cybersecurity history has proven that even in 2017 and subsequent years, serious security vulnerabilities like WannaCry, EternalBlue... on old Windows Server were continuously discovered. When the system cannot be upgraded, the door for hackers is always wide open. An unpatched security vulnerability can cause a business to lose everything overnight.
Preparation for the AI race
We are living in an era of Artificial Intelligence explosion. Microsoft has continuously improved .NET and added libraries optimized for high-performance computing, parallel processing, connecting with AI/Deep Learning models...
If developers do not change their language and platform, they will be isolated, unable to integrate or leverage the power of today's AI algorithms. The system will be completely helpless against intelligent data processing problems.
The constraint of old databases
By deliberately using old .NET in their work, businesses almost have to lock themselves into outdated database management systems like SQL Server 2012, 2016 (old SQL code, stored procedures often don't run on new SQL Server or take a lot of time to rewrite in the new style).
Meanwhile, SQL Server 2025 has fundamentally changed the entire data game. The new architecture deeply integrates AI for intelligent query optimization, supports Native Vector for AI and Native JSON... completely superior to previous SQL Server versions.
The difference is so significant that Microsoft has deprecated the legendary System.Data.SqlClient connection library, which was the backbone of old .NET, on new technology lines.
Leveraging the power of "Server King" Linux
One of Microsoft's century-defining moves was bringing new .NET to the Linux operating system. Linux has long been considered the standard for server operating systems due to its high performance, stability, and cost-saving licensing capabilities.
With new .NET running on Linux, Docker/Kubernetes containerization, scaling, and Load Balancing become easier and more cost-effective than ever. Conversely, old .NET is forced to run on Windows - an operating system that, in today's world of Cloud and Microservices, is no longer considered the optimal standard for large server systems.
Troubleshooting and system monitoring capabilities
When an old .NET system encounters a network congestion or memory overflow issue on the server, finding the cause is like "finding a needle in a haystack"; developers have to manually sift through log files or download multi-GB dump files to analyze IIS errors.
Conversely, new .NET is equipped with modern standards such as OpenTelemetry, intrinsic Metrics counters, and real-time Structured Logging. This allows engineers to see through every data flow, precisely detect which functions are running slowly directly on automated monitoring Dashboards, reducing troubleshooting time from days to minutes.
Human resource crisis issue
Using old .NET means that businesses are self-sabotaging their recruitment capabilities. Talented personnel and new generation young people will certainly refuse to work with a technology that has been "deprecated."
No one wants to bury their career maintaining or developing a pile of outdated source code. The consequence is that businesses will face a human resource shortage crisis, with no one to maintain or develop the system, or only be able to recruit “weak coders.”
Beware of the "New bottle, old wine" trap
Using new .NET with an old .NET mindset is also useless! A crucial point that Mr. Dat frankly exposed during the sharing session: "Upgrading to the new .NET platform is only a necessary condition; changing the programming mindset is the sufficient condition."
The current reality is that there are many projects that claim to run on .NET 8, .NET 9, but developers still maintain "ancient" habits from the .NET Framework 3.0 era: They overuse synchronous functions instead of Async/Await, create cumbersome classes that choke processing threads, manually code initialization functions instead of using Dependency Injection, or worse, still try to cram incompatible old libraries into the system. Some even copy or convert old code with very few changes - while new .NET is truly a completely different tool. The price to pay is that the application still bottlenecks, performance remains sluggish, and the system constantly crashes in a… puzzling way.
To conclude the sharing session, Mr. Dat offered a very valuable analogy:
"A business stubbornly using old .NET from 2015 at this point is exactly like using Visual Basic 1998 to develop a project in 2015 itself."
That's not just technological backwardness; it's business "suicide." The seminar opened up a new vision for the interns: To go far, fast, and safely, we must stand on the latest technologies!
Thank you for Mr. Dat's extremely dedicated and "awakening" sharing!