If you’ve spent most of your SAP career working with SAP ECC, you’re not alone.
For decades, SAP ERP Central Component (SAP ECC) has served as the technological backbone for thousands of organizations worldwide, enabling critical processes across finance, logistics, manufacturing, and more. But as digital transformation accelerates and enterprise demands grow more complex, SAP ECC’s aging architecture has begun to show its limits. This shift has led to the emergence—and growing adoption—of SAP S/4HANA, SAP’s next-generation ERP suite.
In a previous blog post, we explored the functional differences between SAP ECC and SAP S/4HANA. From simplified finance operations to improved logistics processes and embedded analytics, SAP S/4HANA offers a more agile, user-friendly approach to core business functionality. But for many organizations and SAP professionals, understanding the technical differences is just as important (if not more so) when planning a move to SAP S/4HANA.
Table of Contents
- Database Architecture: SAP HANA-Only Foundation
- Data Model Simplification
- Modern ABAP and CDS Views
- UI Technology: SAP GUI vs. SAP Fiori
- Clean Core and Extensibility
- Real-Time Processing vs. Batch Processing
- Custom Code and Compatibility
- API-First and Integration Strategy
- Deployment and Infrastructure Differences
- Conclusion
Why does the technical side matter? Because it’s where the real transformation happens. SAP S/4HANA is not simply a re-skinned version of SAP ECC. It’s a fundamentally different platform with a new foundation: a simplified data model, a modern programming model, a new integration philosophy, and a tightly coupled in-memory database. These backend changes have major implications for performance, system maintenance, extensibility, and future-readiness.
For decision-makers, this means evaluating not only licensing and business process changes but also infrastructure, system performance, and long-term maintainability. For developers and administrators, it means rethinking how they build, extend, and manage SAP systems. And for curious SAP ECC users trying to make sense of the changes, it means learning what’s under the hood and why it matters.
In this post, we’ll walk through the major technical shifts between SAP ECC and SAP S/4HANA. We’ll look at everything from the SAP HANA-only database architecture to the modern ABAP programming model, from real-time processing capabilities to SAP Fiori-based UI development, and from new extensibility models to API-first integrations. Whether you're starting your migration journey or simply want to understand what’s changed, this guide will provide the insight you need to navigate the technical landscape of SAP S/4HANA with confidence.
Database Architecture: SAP HANA-Only Foundation
One of the most fundamental technical changes between SAP ECC and SAP S/4HANA is the shift in database architecture. SAP ECC supports a range of third-party databases, including Oracle, IBM DB2, and Microsoft SQL Server, allowing organizations to choose their preferred database vendor when deploying the ERP system. This flexibility, while useful, also meant that SAP had to optimize its applications to work with different database technologies, many of which were row-based and disk-driven.
SAP S/4HANA, by contrast, is built exclusively for the SAP HANA database. This change is not simply a matter of preference; it’s a strategic architectural decision that fundamentally redefines how the system stores, processes, and retrieves data. SAP HANA is an in-memory, columnar database designed for real-time analytics and high-speed transaction processing. Because data is stored in memory rather than read from disk, operations that once took minutes or hours in SAP ECC can now be executed in seconds or less in SAP S/4HANA.
This shift to SAP HANA has far-reaching technical implications. First, it eliminates the need for many of the aggregate and index tables that were once required to speed up reporting in SAP ECC. Since SAP HANA can perform complex calculations on the fly, these redundant tables are no longer necessary. This not only simplifies the data model but also reduces data redundancy and storage requirements.
Second, the exclusive use of SAP HANA enables the system to run OLTP (transactional) and OLAP (analytical) workloads on the same platform. In SAP ECC, these tasks were typically separated—real-time analytics often required data to be extracted, transformed, and loaded (ETL) into a separate warehouse for reporting. With SAP S/4HANA, many of these reporting needs can now be met directly within the transactional system using technologies like core data services (CDS) views.
Third, the SAP HANA platform unlocks the potential for new capabilities such as predictive analytics, machine learning integration, and advanced planning—thanks to its performance and ability to process large volumes of structured and unstructured data in real time.
However, this shift also means that organizations migrating from SAP ECC to SAP S/4HANA must consider infrastructure readiness. Existing databases must be decommissioned, and system sizing, memory planning, and hardware provisioning must all be re-evaluated for SAP HANA compatibility. For those running on-premise, this may involve significant hardware investments; for cloud deployments, it means understanding how to scale and monitor in-memory resource consumption effectively.
In summary, SAP S/4HANA’s exclusive reliance on the SAP HANA database represents a foundational change in how the ERP system is designed and operated. It delivers faster performance, enables real-time insight, and simplifies data structures—but it also requires careful planning and a clear understanding of the architectural implications for migration, development, and system management.
Data Model Simplification
Closely tied to the shift to the SAP HANA database is one of the most talked-about technical changes in SAP S/4HANA: the simplified data model. While SAP ECC relied on complex, layered table structures—often with multiple aggregate, index, and history tables to support reporting and performance—SAP S/4HANA rethinks this approach from the ground up.
In SAP ECC, these auxiliary tables were essential because traditional databases weren’t optimized for high-speed, on-the-fly calculations. To keep performance acceptable, data had to be pre-aggregated and duplicated across various structures. The result was a system with many interdependent tables, such as BSIS/BSAS for financial postings or VBUK/VBUP for sales document statuses, which increased both complexity and data volume.
SAP S/4HANA, by design, eliminates much of this redundancy. Leveraging SAP HANA, it removes the need for pre-aggregated totals and index tables. Instead, real-time aggregation and calculation are performed dynamically using columnar storage and parallel processing capabilities.
A prime example of this is the Universal Journal table, ACDOCA, which consolidates data from various financial modules such as General Ledger (FI-GL), Controlling (CO), Asset Accounting (AA), and Material Ledger (ML) into a single line-item table. Where SAP ECC maintained separate tables for each module, SAP S/4HANA centralizes this data, making it easier to access, reconcile, and analyze.
This simplification isn’t limited to finance. In logistics and inventory management, tables like MATDOC have been introduced to unify material document data that was previously spread across several tables in SAP ECC. These changes not only reduce the database footprint but also accelerate reporting and improve system transparency.
From a technical standpoint, this means developers, analysts, and system architects must adapt. Custom reports and ABAP code that relied on obsolete tables or assumed certain data structures may need to be rewritten or re-optimized. SAP provides a simplification list that documents these structural changes and helps teams understand what has been removed, merged, or replaced in SAP S/4HANA.
It also means rethinking how data is queried and presented. Rather than pulling from multiple tables and writing heavy joins in ABAP, developers are encouraged to use CDS views to define data models that reflect the simplified structure and take full advantage of SAP HANA's processing power.
Ultimately, the simplified data model in SAP S/4HANA brings greater consistency, faster analytics, and lower maintenance. But it also requires a shift in mindset and development practices for those accustomed to the older, more fragmented architecture of SAP ECC.
Modern ABAP and CDS Views
SAP S/4HANA introduces a major evolution in how developers work within the system. SAP ECC relied heavily on procedural ABAP programming, classic reports, and UI technologies like Dynpro and ALV. In contrast, SAP S/4HANA shifts development toward a more modular, service-oriented model built around the capabilities of the SAP HANA database.
At the heart of this change is CDS views. These are not just database views—they’re semantically rich data definitions that allow developers to model data directly on the database layer. CDS views support features like associations, annotations, and access control, making them a foundational element for UI generation, reporting, and transactional applications.
In SAP ECC, data modeling and business logic were often bundled together inside custom ABAP programs. Reports might include SQL queries, calculations, formatting logic, and UI handling, all in one place. With SAP S/4HANA, these concerns are separated. CDS views handle the data modeling and expose that data for use by SAP Fiori apps, analytics tools, and external APIs. This leads to cleaner, more maintainable code and better system performance.
This shift also supports the new ABAP RESTful application programming model (oftentimes referred to as RAP), which replaces classic development techniques like module pools, user exits, and BAPIs. The model is designed for building modern, cloud-ready applications using a combination of CDS views, behavior definitions, and business services. It provides a structured way to define how data is queried, manipulated, and validated, all in line with SAP’s clean core and extensibility strategies.
For developers coming from SAP ECC, this new model has a learning curve. Traditional ABAP still works in SAP S/4HANA, but it’s no longer the default for new development. Instead, developers need to become comfortable with SQL-based programming, annotations for SAP Fiori enablement, and metadata-driven application design.
Another key change is how performance optimization is handled. In SAP ECC, developers often used buffering, indexes, and manual tuning to improve report performance. With CDS views and SAP HANA, much of that logic is pushed to the database layer, where it can be executed more efficiently. As a result, knowing how to build performant CDS views becomes more important than optimizing ABAP loops.
In short, development in SAP S/4HANA is more declarative, more integrated with the UI and database, and more aligned with modern enterprise software practices. It’s a step toward future-proof application design, but one that requires developers to rethink how they build and maintain custom functionality.
UI Technology: SAP GUI vs. SAP Fiori
One of the most visible changes between SAP ECC and SAP S/4HANA is the user interface. While SAP ECC is primarily accessed through the traditional SAP GUI—a keyboard-driven, transactional interface that hasn’t changed much in decades—SAP S/4HANA introduces a modern, role-based user experience through SAP Fiori.
SAP Fiori is more than just a new look and feel. It represents a shift in how users interact with SAP systems. Built on HTML5 and JavaScript, SAP Fiori apps run in a browser and are designed to be intuitive, responsive, and mobile-ready. Users are presented with personalized launchpads that display only the apps relevant to their roles, reducing the clutter and complexity typical of SAP ECC’s menu-driven navigation.
From a backend perspective, this change significantly impacts developers and system architects. While SAP ECC transactions are tightly bound to SAP GUI screens and ABAP dynpros, SAP Fiori apps consume data via OData services (RESTful APIs that expose business objects and operations). These services are typically built on top of CDS views and require additional metadata annotations to support SAP Fiori-specific behaviors like value help, UI labels, and field grouping.
This means backend developers must now be familiar not only with ABAP and CDS, but also with concepts from the web development world, such as service provisioning, data binding, and UI annotations. In some cases, developers also collaborate with frontend specialists who work with SAPUI5, SAP’s UI framework built on JavaScript.
It's important to note that SAP GUI is still supported in SAP S/4HANA, and many classic transactions remain available, especially in the on-premise edition. However, SAP is investing heavily in expanding its library of SAP Fiori apps and encourages customers to adopt SAP Fiori-first designs for new developments and user-facing scenarios. Many key innovations, like embedded analytics and situation handling, are only available through SAP Fiori interfaces.
For system administrators, the shift also introduces new technical components, such as the SAP Fiori front-end server, which handles the delivery of apps, authentication, and communication with backend OData services. Understanding how to configure, secure, and scale these components becomes critical in a production SAP S/4HANA landscape.
In summary, SAP Fiori offers a more user-friendly and future-ready interface, but it requires a new way of thinking for those accustomed to SAP GUI. Developers must embrace service-oriented design, and administrators must learn to manage new layers of the application stack—all in support of a more modern and accessible SAP experience.
Clean Core and Extensibility
In SAP ECC, customizing and enhancing the system often meant modifying the core. This included directly changing standard programs, using user exits, implementing customer-specific Z-transactions, or adding enhancements at predefined points in the code. While effective in the short term, this approach made upgrades and system maintenance more complex and risk prone. Each modification introduced a potential conflict during future updates, slowing down innovation cycles and increasing the total cost of ownership.
SAP S/4HANA introduces a new extensibility model built around the principle of maintaining a clean core. The idea is simple but powerful: keep the standard SAP codebase untouched and extend the system through well-defined, upgrade-safe layers. This approach makes it easier to adopt innovations, apply updates, and remain compliant with cloud deployment models, especially for customers considering SAP S/4HANA Cloud or RISE with SAP.
There are three extensibility approaches in SAP S/4HANA: key user extensibility, developer extensibility, and side-by-side extensibility.
Key user extensibility and developer extensibility are available directly within the SAP S/4HANA system. Key user extensibility is a low code feature intended for key users and consultants, while developer extensibility is “pro code,” offering more typical programming features for ABAP developers. These extensibility options include capabilities such as adding custom fields, creating new CDS views, building UI adaptations, and defining business logic using low code key user tools and the ABAP RESTful application programming model. These changes are recorded in a separate layer and follow SAP’s clean core principles, ensuring that they remain stable through upgrades.
Side-by-side extensibility refers to the use of external platforms—most notably SAP Business Technology Platform (SAP BTP)—to build and run custom applications and services that integrate with SAP S/4HANA. This method uses APIs, events, and service-based integration to connect external apps to core business processes without changing the core system. It’s particularly useful for building customer-specific apps, integrating third-party systems, or adding advanced capabilities such as machine learning or chatbot support.
This shift toward extensibility by design also changes the way developers work. Instead of embedding custom logic directly in a transaction, developers now expose business functionality through CDS views and business services, annotate them with metadata, and connect them to SAP Fiori UIs or side-by-side apps. It requires a broader skill set that includes service-oriented design, clean code practices, and integration expertise.
Ultimately, the clean core strategy encourages organizations to think more strategically about their customizations. It promotes long-term maintainability, reduces technical debt, and lays the foundation for faster innovation—especially in cloud and hybrid environments. For teams migrating from SAP ECC, this may mean re-evaluating existing enhancements and redesigning them to fit SAP S/4HANA’s extensibility framework.
Real-Time Processing vs. Batch Processing
We already mentioned that one of the major technical breakthroughs in SAP S/4HANA, made possible by SAP HANA, is the move from traditional batch processing to real-time data handling. Gone are the days of running scheduled overnight, background jobs to handle large volumes of data. SAP S/4HANA is designed to process data in real time wherever possible.
With SAP S/4HANA, these constraints are significantly reduced. For example, MRP Live in SAP S/4HANA allows planners to perform material planning in real time, reflecting the latest stock levels and demand signals without waiting for a nightly job to complete.
This shift affects more than just speed. It changes how businesses operate. Real-time insights allow for more agile decision-making, faster exception handling, and a more responsive supply chain. Financial reconciliation, for example, can be performed continuously instead of just at month end, improving visibility into cash flow and profit margins throughout the period.
On the technical side, this also changes how systems are designed and monitored. In SAP ECC, developers and administrators were accustomed to building complex batch frameworks, handling lock conflicts, and troubleshooting performance issues tied to long-running jobs. In SAP S/4HANA, these same professionals are encouraged to rethink these processes—optimizing them for in-memory execution and reengineering them to eliminate unnecessary delays or redundancies.
It’s important to note that batch jobs haven’t disappeared entirely. Many processes still run in the background, and SAP S/4HANA supports legacy batch frameworks. But the expectation is shifting: real-time is now the default, and batch is reserved for truly asynchronous or high-volume scenarios.
This change presents an opportunity for IT teams to revisit long-standing pain points in system performance and process latency. By modernizing these jobs and processes, organizations can reduce processing windows, minimize downtime, and create more responsive and user-friendly systems.
Custom Code and Compatibility
Custom code has long been a core part of SAP implementations. In SAP ECC, many organizations developed significant volumes of custom ABAP code to fill functional gaps, automate tasks, or tailor standard processes to business-specific needs. While this flexibility was one of SAP ECC’s strengths, it also created challenges, especially when it came to upgrades, system performance, and long-term maintainability.
With SAP S/4HANA, custom code compatibility becomes a central concern. Because of the significant architectural and data model changes—such as the removal of aggregate and index tables, and the consolidation of financial and logistics tables—much of the custom code written for SAP ECC will no longer function correctly without adjustment.
A key example is the use of tables like BSEG, BSIS, or VBUK, which are commonly accessed directly in SAP ECC custom programs. In SAP S/4HANA, many of these tables have been replaced, deprecated, or restructured. Direct table reads that worked in the past may now return incomplete or misleading data—or cause performance issues when run on SAP HANA.
To address this, SAP provides several tools to help identify and adapt affected custom code. One of the most important is the SAP Readiness Check, which analyzes the existing SAP ECC system and highlights areas of incompatibility, including obsolete function modules, modified standard objects, and deprecated data elements. Developers can also use the Simplification Database and the Custom Code Migration Worklist to prioritize which programs need to be adjusted or rewritten.
Another essential tool is the ABAP Test Cockpit, which allows organizations to scan their codebase for syntax errors, performance issues, and violations of SAP S/4HANA development guidelines. By integrating the cockpit checks into the development workflow, teams can ensure their code aligns with SAP’s best practices and is ready for the new system landscape.
Adapting custom code for SAP S/4HANA often goes beyond simple syntax fixes. Developers must understand the intent of the original code and determine whether it can be replaced with standard functionality, re-implemented using CDS views and OData services, or redesigned to align with the clean core extensibility approach. This presents an opportunity not only to modernize the codebase but to reduce technical debt and eliminate outdated or redundant logic.
In many cases, businesses discover that their customizations are no longer needed, as SAP S/4HANA provides more built-in functionality, flexible configuration options, and advanced reporting tools than SAP ECC. This can further reduce the maintenance burden and improve system stability.
Ultimately, while the custom code transition can be one of the more time-consuming aspects of an SAP S/4HANA migration, it’s also one of the most valuable. By taking a strategic, tool-assisted approach to custom code remediation, organizations can ensure a smoother migration and position themselves for long-term agility and innovation.
API-First and Integration Strategy
SAP ECC was built in an era when most enterprise integrations were done through tightly coupled systems, often using proprietary protocols like remote function calls, file transfers, and intermediate documents. While these methods were effective, they were not always flexible, scalable, or suitable for modern, cloud-based environments.
SAP S/4HANA introduces a new integration philosophy: API-first. This means that SAP prioritizes the creation and publication of standardized, reusable APIs to connect SAP S/4HANA with other SAP products, third-party systems, cloud platforms, and custom applications.
In SAP ECC, integrations often required complex middleware or point-to-point connections. Custom interfaces relied heavily on deep knowledge of internal table structures and transaction flows. In SAP S/4HANA, integrations are exposed through well-documented RESTful APIs, often based on OData or SOAP, and cataloged centrally via the SAP API Business Hub. This makes it easier for developers and partners to find, test, and reuse APIs, whether for real-time data exchange, event handling, or external application access.
This shift also ties closely into SAP’s broader cloud and platform strategy, especially with SAP BTP. The platform serves as the hub for side-by-side extensibility, workflow orchestration, and integration services. With tools like SAP Integration Suite, organizations can build, manage, and monitor integrations across hybrid landscapes using prebuilt content and connectors for SAP and non-SAP systems.
In addition, SAP S/4HANA supports event-driven architectures through integration with technologies like SAP Event Mesh and SAP BTP’s messaging services. Rather than polling systems or relying on scheduled updates, applications can now subscribe to business events (such as a sales order creation or delivery completion) and react in real time. This opens the door to loosely coupled microservices, more efficient automation, and scalable cloud-native designs.
For IT teams, this means a significant change in how integrations are planned, built, and maintained. Skills in API development, security (such as OAuth 2.0), JSON payloads, and asynchronous messaging are increasingly important. It also means that traditional ABAP-centric interfaces may need to be re-evaluated or replaced with more modern, open solutions that align with SAP’s future roadmap.
SAP’s move to API-first integration is not just a technical upgrade. It’s a strategic enabler for digital transformation. It allows organizations to connect SAP S/4HANA to mobile apps, customer portals, partner systems, and analytics tools in ways that were much harder to achieve with SAP ECC’s legacy frameworks.
Deployment and Infrastructure Differences
The final major technical shift between SAP ECC and SAP S/4HANA lies in how the systems are deployed, managed, and scaled. SAP ECC was almost exclusively deployed on-premise.
Organizations purchased or leased their own hardware, managed their own operating systems and databases, and controlled all aspects of infrastructure planning, monitoring, and maintenance. While this offered a high degree of control, it also came with heavy infrastructure overhead and long provisioning cycles.
SAP S/4HANA, on the other hand, offers a range of deployment options designed to meet different organizational needs and support SAP’s cloud-centric vision. Customers can choose to run SAP S/4HANA:
- On-premise, maintaining full control over the system landscape
- In the cloud, using SAP S/4HANA Cloud (on a dedicated [private] or shared [public] server)
- Through RISE with SAP, a subscription-based, bundled offering that includes infrastructure, licenses, support, and SAP-managed services
Each option comes with different technical responsibilities. In an on-premise setup, the organization remains responsible for infrastructure and system administration, much like with SAP ECC—but with the added complexity of provisioning and maintaining the SAP HANA database. In the cloud, many of those responsibilities shift to SAP or a cloud provider, depending on the deployment model. For example, in the SAP S/4HANA Cloud public edition, customers have limited access to the backend and focus more on configuration and extensibility rather than custom development or system tuning.
From a technical operations perspective, this means that teams need to become familiar with managing hybrid landscapes, monitoring cloud-based resources, and working within more standardized, often locked-down, environments. Tools like SAP Cloud ALM (for cloud and hybrid systems), SAP Solution Manager (for strictly on-premise systems), and integration services in SAP BTP become essential for monitoring, lifecycle management, and automated updates.
Deployment choice also affects the release strategy. SAP ECC followed a traditional model where customers chose when and how to apply upgrades. SAP S/4HANA Cloud, especially the public edition, follows a continuous delivery model with quarterly updates. This means that technical teams must be prepared for more frequent testing, regression checks, and adaptation of custom enhancements to remain compatible with the latest release.
Another major shift is infrastructure scalability. While scaling SAP ECC typically required significant manual intervention—adding hardware, resizing systems, or provisioning new environments—SAP S/4HANA’s cloud deployments can scale more dynamically. Cloud infrastructure providers offer flexible sizing, high availability options, and geographic distribution that would be difficult or costly to implement on-premise.
As a result, the move to SAP S/4HANA is not just about updating the software. It often means updating your infrastructure strategy. IT teams need to evaluate whether to retain full control through an on-premise setup, shift some responsibilities to the cloud with the private edition, or adopt a standardized, SaaS-style approach through the public edition or RISE with SAP. Each path brings different trade-offs in terms of customization, speed of innovation, and technical control.
In all cases, the infrastructure underpinning SAP S/4HANA is built for agility, real-time performance, and integration with the broader digital enterprise. Embracing these options means rethinking not just how SAP is deployed, but how it fits into the organization’s long-term IT roadmap.
Conclusion
The transition from SAP ECC to SAP S/4HANA is more than a software upgrade—it’s a shift in how organizations design, develop, operate, and extend their ERP systems. While much of the conversation around SAP S/4HANA has focused on functional improvements, the technical changes are just as significant—and in many cases, more transformative.
SAP S/4HANA introduces a streamlined, high-performance architecture built on a proprietary in-memory database. It simplifies data models, introduces modern development tools like CDS and the ABAP RESTful application programming model, and replaces monolithic transaction screens with role-based SAP Fiori apps. The extensibility model encourages organizations to keep the core clean and innovate safely through on stack and side-by-side enhancements. Real-time processing replaces traditional batch frameworks, and integration is reimagined through API-first principles and cloud-native tooling.
These changes come with a learning curve, especially for teams that have spent years working within SAP ECC's familiar structure. But they also offer an opportunity: an opportunity to streamline system landscapes, reduce technical debt, improve agility, and better align IT with business goals. With the right planning, training, and tools, technical teams can use this transition not just to modernize their systems, but to future-proof their organizations.
Whether you're a developer updating custom code, a system architect planning infrastructure, or a decision-maker weighing your deployment options, understanding the technical foundation of SAP S/4HANA is essential. The more prepared your team is for these backend changes, the more successful (and sustainable) your move to SAP S/4HANA will be.
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