Contents
Focus on practical problem-solving over theoretical knowledge to spot AS400 experts who can manage legacy systems and modernisation challenges.
Assess core competencies including RPG programming, system architecture, debugging, performance tuning, and secure operations.
Evaluate candidates’ experience in integrating AS400 with modern web applications and APIs using real-world scenario questions.
Check for understanding of critical system operations like job types, library management, and commitment control.
Look for strategic skills such as designing high-availability solutions, capacity planning, and proactive modernization approaches.
Prioritize candidates who demonstrate strong communication, mentoring abilities, and a commitment to knowledge transfer for sustainable team growth.
Understanding the Current AS400 Landscape
AS400 interview questions usually test CL commands, RPG syntax, and DB2 queries. Candidates demonstrate knowledge of job queues and subsystems perfectly. But legacy systems demand more than command memorization.
When critical business processes fail or performance degrades, you need developers who understand how these systems actually work in production environments. Theory breaks down when dealing with decades-old code that keeps your business running.
While demand for legacy system expertise grows, finding qualified candidates who can bridge traditional AS400 operations with modern business needs becomes increasingly challenging.
This guide provides engineering teams with a strategic framework for evaluating AS400 talent across all experience levels, from fresh graduates to seasoned experts.
AS400 systems, now known as IBM i or iSeries, continue powering critical business operations across industries. Despite being labeled "legacy," these systems handle mission-critical workloads for manufacturing, finance, and logistics companies worldwide.
The challenge isn't just finding AS400 developers. You need professionals who understand both traditional system operations and modern integration requirements. These hybrid skills ensure your legacy investments remain valuable while supporting digital transformation initiatives.
Key Market Realities:
AS400 professionals with 5+ years experience command 20-30% salary premiums
60% of Fortune 500 companies still rely on AS400 systems for core operations
Average time-to-fill for senior AS400 positions exceeds 90 days
Only 15% of computer science graduates receive AS400 training
Beyond Resume Screening: Real AS400 Competency Assessment
Traditional hiring approaches fail because they focus on surface-level knowledge rather than practical problem-solving abilities. A candidate might memorize RPG syntax but struggle with real-world debugging scenarios.
Common Screening Mistakes:
Prioritizing certification count over hands-on experience
Testing theoretical knowledge instead of practical application
Ignoring soft skills crucial for legacy system maintenance
Overlooking modernization mindset for integration projects
Effective AS400 assessment requires understanding how candidates approach system-level thinking, not just programming syntax.
Did you know?
IBM AS400, aka IBM i, integrates hardware, OS, and database into a single, reliable platform for business-critical workloads.
Why Trust Utkrusht with AS400 Hiring?
AS400 remains crucial to many enterprises. Utkrusht’s assessment platform tests real troubleshooting and modernisation skills beyond certifications. Join to shortlist candidates who truly understand both legacy systems and modern integration challenges, reducing costly hiring mistakes.
AS400 Interview Questions for Freshers
Fresh graduates or entry-level candidates need foundational knowledge assessment. Focus on basic concepts and learning potential rather than extensive experience.
1. What is AS400 and why is it still relevant in modern businesses?
AS400, now called IBM i, is an integrated midrange server platform combining hardware, operating system, and database in a single solution. It remains relevant because of its stability, security, and ability to handle high-volume transaction processing. Many businesses rely on AS400 for ERP systems, financial processing, and manufacturing operations where reliability is critical.
2. Explain the difference between a physical file and a logical file in AS400.
A physical file actually stores data on disk, similar to a table in relational databases. A logical file provides a view or access path to data in physical files without storing data itself. Logical files can sort, select, or join data from multiple physical files, enabling different data presentations without duplicating storage.
3. What are the main components of the AS400 architecture?
AS400 architecture includes the hardware layer (POWER processors), OS/400 operating system, integrated DB2 database, and middleware components. The Technology Independent Machine Interface (TIMI) separates software from hardware, allowing applications to run across different hardware generations without modification.
4. How do you create a simple RPG program to display "Hello World"?
H DFTACTGRP(*NO) ACTGRP(*NEW)
D msg S 20A INZ('Hello World')
C DSPLY msg
C RETURN
5. What is the purpose of DDS (Data Description Specifications)?
DDS defines the structure and characteristics of database files, display files, and printer files. It specifies field attributes, record formats, keywords for validation, and relationships between files. DDS acts as a blueprint for how data is organized and accessed within the AS400 system.
Component | Purpose | Key Features |
Physical Files | Data Storage | Record formats, field definitions |
Logical Files | Data Access | Views, sorting, selection criteria |
Display Files | User Interface | Screen layouts, field validation |
Printer Files | Report Output | Formatting, page control |
6. What are the different types of jobs in AS400?
AS400 has three main job types:
Interactive jobs: User-initiated sessions providing immediate feedback
Batch jobs: Background processing without user interaction
System jobs: Handle operating system functions and maintenance tasks
7. Explain the concept of libraries in AS400.
Libraries are containers that organize objects like programs, files, and other resources. They function similarly to directories in other operating systems. The library list determines search order when accessing objects. Common library types include system libraries (QSYS), product libraries, and user-defined libraries.
8. What is the CHAIN operation in RPG?
CHAIN retrieves a specific record from a file using a key value. It provides random access to records and sets indicators to show whether the operation succeeded. CHAIN also locks the record to prevent concurrent modifications.
9. How do you handle errors in RPG programs?
Error handling uses operation extenders and built-in functions:
*ERROR operation extender prevents program termination
%ERROR built-in function checks if errors occurred
MONITOR/ON-ERROR/ENDMON blocks provide structured exception handling
File Information Data Structures (INFDS) capture file-specific errors
10. What is commitment control in AS400?
Commitment control ensures transaction integrity by grouping related database changes into logical units of work. It supports COMMIT to save changes permanently or ROLLBACK to undo changes if errors occur. This prevents partial updates that could corrupt data consistency.
Did you know?
Over 60% of Fortune 500 companies still rely on AS400 systems in 2025.
AS400 Interview Questions for 7 Years Experience
Mid-level candidates should demonstrate practical experience with system administration, advanced programming concepts, and integration challenges.
11. How would you optimize a poorly performing RPG program?
Performance optimization involves:
Analyzing program logic for unnecessary loops or calculations
Using appropriate file access methods (arrival sequence vs keyed access)
Implementing proper indexing on database files
Optimizing SQL statements with execution plans
Reducing I/O operations through record blocking
Using arrays instead of multiple variables where appropriate
12. Describe your approach to implementing a subfile for data entry.
Subfile implementation requires:
Defining SFL record format for data display
Creating SFLCTL record format for subfile control
Implementing load, display, and update logic
Handling page-up/page-down functionality
Validating data before database updates
Managing subfile indicators for display options
13. How do you integrate AS400 with modern web applications?
Integration approaches include:
Web services using IBM i Web Services Server
REST APIs through IBM HTTP Server
Database connectivity via ODBC/JDBC drivers
Message queuing for asynchronous communication
File transfer protocols (FTP, SFTP) for batch processing
Modern tools like RPG-XML Suite for data exchange
14. Explain ILE (Integrated Language Environment) concepts.
ILE enables modular programming through:
Modules: Compiled source members that aren't executable
Service Programs: Collections of reusable procedures
Binding: Process of combining modules into programs
Activation Groups: Runtime environments managing program resources
Prototyping: Defining procedure interfaces for type checking
15. How do you implement proper security in AS400 applications?
Security implementation includes:
Object-level security controlling access to programs and files
Field-level security restricting sensitive data access
User profile management with appropriate authorities
Exit programs for customized security rules
Encryption for sensitive data storage and transmission
Audit trails tracking user activities and changes
16. Describe your experience with AS400 database journaling.
Database journaling provides:
Change tracking for audit and recovery purposes
Point-in-time recovery capabilities
Remote journaling for high availability setups
Commitment control support for transaction management
Performance considerations for journal management
17. How do you handle large file processing efficiently?
Efficient processing techniques:
Block processing to reduce I/O overhead
Proper file access paths using logical files
Array processing for bulk operations
SQL set-based operations instead of record-by-record processing
Parallel processing where appropriate
Memory management for large data sets
18. What strategies do you use for AS400 system backup and recovery?
Backup strategies include:
SAVLIB for individual library backups
SAVSYS for complete system saves
Incremental saves for changed objects only
Remote save locations for disaster recovery
Save-while-active technology for online backups
Testing restore procedures regularly
19. How do you troubleshoot communication issues between AS400 and external systems?
Troubleshooting steps:
Checking network connectivity with PING
Verifying TCP/IP configuration and routes
Examining job logs for error messages
Testing with TELNET or FTP for basic connectivity
Analyzing communication trace data
Reviewing firewall and security settings
20. Explain your approach to AS400 capacity planning.
Capacity planning involves:
Monitoring CPU utilization and response times
Analyzing disk storage growth patterns
Tracking memory usage and paging rates
Evaluating I/O bottlenecks and disk arm utilization
Planning for peak processing periods
Considering workload growth projections
Did you know?
AS400’s RPG programming language dates back to the late 1960s but remains actively used and evolved[attached file].
AS400 Interview Questions for Advanced Experience
Senior professionals should demonstrate strategic thinking, architecture design, and leadership in complex AS400 environments.
21. Design a high-availability solution for mission-critical AS400 applications.
High-availability architecture includes:
Primary and secondary systems with real-time data replication
Geographic distribution for disaster recovery
Load balancing for application availability
Automated failover mechanisms using PowerHA SystemMirror
Regular testing of failover procedures
Network redundancy and storage mirroring
Recovery time objectives (RTO) and recovery point objectives (RPO) planning
22. How would you modernize a legacy AS400 application while maintaining business continuity?
Modernization strategy:
Phase-wise migration approach minimizing disruption
API layer creation for system integration
User interface modernization through web technologies
Database optimization and normalization
Code refactoring for maintainability
Parallel running of old and new systems during transition
Comprehensive testing and rollback procedures
23. Describe your approach to AS400 performance tuning at the system level.
System-level tuning involves:
Memory pool allocation based on workload patterns
Storage pool management and disk arm balancing
Job queue configuration for optimal throughput
System value adjustments for specific workloads
SQL query optimization and index strategy
Work management tuning for subsystem performance
Regular performance monitoring and trend analysis
24. How do you implement DevOps practices in AS400 environments?
DevOps implementation includes:
Source code management using Git integration
Automated build processes for RPG and CL programs
Continuous integration pipelines for testing
Deployment automation across environments
Configuration management for system settings
Monitoring and logging integration
Collaboration tools bridging AS400 and modern development
25. Explain your strategy for AS400 skills transfer and knowledge management.
Knowledge management approach:
Documentation standards for programs and procedures
Mentoring programs pairing experienced and junior developers
Code review processes ensuring quality and knowledge sharing
Training programs for modern AS400 technologies
Cross-training initiatives reducing single points of failure
Knowledge repositories capturing institutional wisdom
Regular architecture reviews and decision documentation
Did you know?
DDS (Data Description Specifications) define file layouts and are unique to AS400 system programming[attached file].
Scenario-Based AS400 Interview Questions
Real-world scenarios test practical problem-solving abilities and decision-making skills.
26. Your production AS400 system experiences sudden performance degradation. Walk me through your diagnostic process.
Diagnostic approach:
Check system status using WRKSYSSTS and WRKACTJOB
Identify resource bottlenecks (CPU, memory, disk I/O)
Examine job queues for backed-up batch processing
Review recent changes to programs or system configuration
Analyze long-running jobs and SQL statements
Check for lock contention or deadlock situations
Examine system messages and error logs
Implement immediate relief measures while planning permanent fixes
27. A critical business file becomes corrupted during processing. How do you recover with minimal data loss?
Recovery procedure:
Stop all jobs accessing the corrupted file immediately
Assess corruption extent using file verification utilities
Restore from most recent backup if corruption is extensive
Apply journal entries from backup point to corruption time
Verify data integrity after recovery
Implement additional validation checks to prevent recurrence
Document incident and update backup procedures if necessary
28. Your AS400 system needs to integrate with a cloud-based CRM system. Design the integration architecture.
Integration design:
API gateway for secure cloud connectivity
Data transformation layer handling format differences
Message queuing for reliable asynchronous communication
Error handling and retry mechanisms
Data synchronization scheduling and monitoring
Security implementation including encryption and authentication
Fallback procedures for connectivity issues
Performance monitoring and optimization
29. Management requests real-time reporting capabilities from AS400 data. How do you implement this requirement?
Real-time reporting solution:
Database replication to reporting server to avoid production impact
Web-based dashboard using modern BI tools
API development for data access from reporting applications
Caching strategies for frequently accessed data
Incremental data updates to minimize processing overhead
User access controls and data security measures
Performance optimization for complex queries
30. You discover security vulnerabilities in legacy AS400 programs. Outline your remediation plan.
Security remediation plan:
Immediate risk assessment and temporary mitigation measures
Inventory of affected programs and their criticality
Priority ranking based on risk exposure and business impact
Code review process identifying specific vulnerabilities
Remediation implementation with proper testing procedures
Security testing validation before production deployment
Enhanced security standards for future development
Regular security audits and penetration testing
Did you know?
AS400 systems support multiple job types: interactive, batch, and system jobs to handle varied workloads efficiently.
Tricky AS400 Interview Questions
These questions test deep understanding and problem-solving abilities under pressure.
31. Explain why you might get a "Level Check Error" and how to resolve it without losing data.
Level Check Errors occur when program-described files don't match actual file formats. This happens after field additions, deletions, or modifications. Resolution involves:
Using CHGPF with LVLCHK(*NO) parameter for temporary access
Recompiling programs with updated file definitions
Using CPYF to transfer data to correctly formatted files
Implementing proper change management procedures
Never ignoring level checks as they indicate format mismatches
32. You have a program that randomly locks up without error messages. How do you debug this situation?
Debugging approach:
Use STRSRVJOB to monitor program execution remotely
Add debug statements or DSPLY operations to track program flow
Check for infinite loops or resource contention
Examine file locks and commitment control status
Review program logic for conditional loops without proper exit conditions
Use program trace facilities to identify hanging points
Check for communication timeouts or external resource dependencies
33. How would you handle a situation where SAVLIB fails due to objects being in use?
Handling SAVLIB failures:
Use ENDSBS to end subsystems gracefully and stop active jobs
Implement SAVACT (Save-while-Active) for online saves
Save individual objects using SAVOBJ with specific timing
Use job scheduling to perform saves during low-activity periods
Implement proper save strategies with user notification
Consider alternative backup methods like journaling for critical files
34. A batch job is consuming excessive CPU and needs immediate attention. What are your options?
Immediate response options:
Use CHGJOB to reduce job priority temporarily
Move job to different subsystem with controlled resources
Hold the job (HLDJOB) to investigate resource consumption
End job if it's non-critical and causing system-wide impact
Analyze job characteristics to understand resource usage patterns
Implement job monitoring to prevent future occurrences
36. How do you handle version control for AS400 objects when multiple developers work on the same codebase?
Version control strategy:
Implement source member management with naming conventions
Use change management software tracking modifications
Establish check-out/check-in procedures preventing conflicts
Maintain separate development libraries for each programmer
Create promotion procedures moving code through environments
Document change requests and approvals
Implement automated backup of source members
37. A user reports that a report shows incorrect totals. How do you systematically identify the root cause?
Systematic debugging:
Reproduce the issue in a controlled environment
Trace program execution to identify calculation points
Verify input data accuracy and completeness
Check program logic for mathematical operations
Compare current results with known good historical data
Examine recent program changes or data modifications
Validate report formatting and field mapping
Test with simplified data sets to isolate variables
38. Describe a situation where you would implement data queues instead of database files.
Data queue scenarios:
Real-time communication between programs
Event notification systems requiring immediate response
Temporary data storage for processing workflows
Asynchronous message passing between subsystems
Performance-critical applications avoiding file I/O overhead
Integration with external systems requiring message queuing
Load balancing work distribution across multiple processes
39. How would you optimize an SQL query that performs well in development but poorly in production?
Production optimization:
Analyze execution plans comparing environments
Examine data volume differences affecting performance
Review index usage and creation requirements
Check statistics currency for query optimizer
Consider query rewriting with different join strategies
Implement query result caching where appropriate
Monitor concurrent execution impact on performance
40. A critical program worked yesterday but fails today with no apparent changes. What's your diagnostic approach?
Systematic diagnosis:
Check system messages and job logs for error details
Verify file availability and authority settings
Examine recent system changes including PTF installations
Review backup and recovery operations that might affect files
Check system values and configuration changes
Verify library list and object resolution
Test with known good data to isolate data-related issues
Compare current environment with previous working state
Building Effective AS400 Interview Processes
Multi-Stage Assessment Framework:
Initial Screening (30 minutes): Basic technical knowledge and communication skills
Technical Deep Dive (90 minutes): Hands-on coding and problem-solving scenarios
System Design Discussion (60 minutes): Architecture and integration challenges
Cultural Fit Assessment (45 minutes): Team collaboration and change management
Technical Panel Composition:
Senior AS400 developer for technical depth evaluation
Infrastructure manager for system administration assessment
Business analyst for requirements understanding verification
Team lead for collaboration and communication evaluation
Time-Efficient Screening Methods:
Pre-interview technical questionnaire filtering basic knowledge
Code review exercises using actual business scenarios
Whiteboard sessions for system design thinking
Reference checks focusing on specific technical achievements
Did you know?
IBM’s Technology Independent Machine Interface (TIMI) enables AS400 programs to run unchanged across hardware generations.
Future-Proofing Your AS400 Team
Hybrid Skill Requirements:
Modern AS400 professionals need traditional system knowledge plus contemporary integration capabilities. Look for candidates who understand both legacy operations and modern development practices.
Key Competency Areas:
Traditional AS400 programming and administration
Web services and API development experience
Cloud integration and modernization awareness
DevOps practices and automation tools
Business process understanding beyond technical implementation
Succession Planning Strategies:
Cross-training initiatives reducing knowledge silos
Mentoring programs transferring institutional knowledge
Documentation standards preserving critical information
Modern tooling adoption attracting younger talent
Career development paths maintaining engagement
Did you know?
AS400 supports high availability setups via replication and failover, critical for minimizing downtime.
Conclusion and Action Items
Effective AS400 hiring requires moving beyond traditional technical questioning toward comprehensive assessment of problem-solving abilities, modernization mindset, and business understanding.
Your Next Steps:
Revise job descriptions emphasizing hybrid skills combining traditional AS400 expertise with modern integration capabilities
Develop scenario-based assessments using actual business challenges rather than theoretical problems
Create structured interview guides ensuring consistent evaluation across all candidates
Build diverse interview panels including technical, business, and cultural perspectives
Establish clear evaluation criteria balancing technical competency with soft skills and growth potential
Long-term Considerations:
Invest in knowledge transfer programs preserving institutional wisdom
Develop career progression paths keeping AS400 professionals engaged
Plan modernization initiatives that enhance rather than replace AS400 capabilities
Build partnerships with educational institutions developing AS400 curriculum
The goal isn't just finding someone who knows AS400 syntax. You need professionals who understand how legacy systems integrate with modern business requirements while maintaining the reliability and security that make AS400 systems indispensable.
Focus on candidates who demonstrate both technical depth and strategic thinking. These individuals will drive your organization's digital transformation while preserving the stability that AS400 systems provide.
AS400 Professionals: Stand Out Fast!
Master practical AS400 skills through hands-on challenges on Utkrust. Grow your expertise in RPG programming, system tuning, and integration with today’s technologies—and get noticed by top employers valuing hybrid skills.
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