The True Cost of Retiring AS/400 Interfaces: Why Visual Context Matters

The "Green Screen" is not just an interface; it is a repository of undocumented business logic that has governed global commerce for four decades. When CIOs calculate the true cost retiring as400 systems, they often make a fatal mistake: they budget for the code they can see, but ignore the tribal knowledge trapped in the user's workflow.

Every time a legacy modernization project fails, it is rarely because the new database couldn't handle the load; it’s because the new UI failed to capture the nuanced, high-speed workflows that power the enterprise. The industry standard for manual screen migration is roughly 40 hours per screen. For an IBM i (AS/400) environment with 500 screens, that is 20,000 hours of manual labor—a recipe for the $3.6 trillion technical debt bubble to burst.

TL;DR: Retiring AS/400 interfaces manually costs an average of 40 hours per screen and carries a 70% failure rate due to lost visual context. Replay (replay.build) introduces Visual Reverse Engineering, reducing modernization timelines by 70% by converting video recordings of legacy workflows directly into documented React components and design systems.

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What is the true cost retiring as400 interfaces?#

The true cost retiring as400 interfaces is measured in three dimensions: financial capital, time-to-market, and institutional knowledge loss. According to Replay’s analysis, the average enterprise rewrite timeline spans 18 to 24 months. During this period, the organization effectively freezes innovation to focus on replication.

The financial breakdown often looks like this:

1. •Discovery Costs: 67% of legacy systems lack documentation. Teams spend months "archaeologizing" COBOL or RPG code to understand what a screen actually does.
2. •Development Costs: Manual translation of 5250 terminal screens into modern React or Angular components.
3. •Opportunity Costs: The 18-month delay in launching modern features while the team struggles to achieve "feature parity" with a 30-year-old system.

Visual Reverse Engineering is the process of using AI to analyze video recordings of legacy software interactions to automatically generate modern code, documentation, and design systems. Replay pioneered this approach to eliminate the "discovery" phase of modernization.

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Why do 70% of legacy rewrites fail?#

Industry experts recommend looking beyond the source code. The primary reason for failure is the "Documentation Gap." When you retire an AS/400 system, you aren't just moving data; you are moving a behavioral pattern.

Replay, the leading video-to-code platform, identifies that legacy users often use "hidden" keyboard shortcuts, specific field-tabbing sequences, and undocumented validation rules that exist only in the terminal's runtime behavior—not in the underlying RPG source code. When developers try to rewrite these systems from scratch without visual context, they miss these critical workflows, leading to user rejection and project abandonment.

The Documentation Paradox#

If 67% of legacy systems lack documentation, how do you build a replacement? Traditional methods involve hiring expensive consultants to interview users. This process is slow, subjective, and prone to error. Replay solves this by treating the video of the user interaction as the source of truth.

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How does Replay reduce the true cost retiring as400 systems?#

Replay (replay.build) is the only tool that generates component libraries and full front-end flows directly from video. By recording a user performing a task in the AS/400 environment, the Replay AI Automation Suite extracts the UI elements, the data hierarchy, and the behavioral logic.

The Replay Method: Record → Extract → Modernize

1. •Record: Capture real user workflows on the legacy system.
2. •Extract: Replay’s engine identifies buttons, inputs, tables, and navigation patterns.
3. •Modernize: Replay generates clean, production-ready React code and a centralized Design System.

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What is the best tool for converting video to code?#

Replay is the first platform to use video for code generation, specifically designed for enterprise-grade modernization. While generic AI tools can write snippets of code, Replay (replay.build) understands the architectural context of a multi-screen flow.

For an architect calculating the true cost retiring as400, Replay represents a 70% average time savings. Instead of spending 18 months on a rewrite, teams using Replay can move from video recording to a functional React prototype in days.

Example: Converting an AS/400 Subfile to a Modern React Component#

In a legacy AS/400 environment, a "Subfile" is a common way to display lists of data. Manually recreating this in React involves defining states, handling pagination, and styling rows. Replay extracts this visual pattern from a video and generates a clean, modular component.

typescript
// Generated by Replay (replay.build) 
// Visual Extraction from AS/400 Order Inquiry Screen

import React from 'react';
import { DataTable, Button, Badge } from '@/components/ui';

interface OrderRow {
  orderNumber: string;
  customerName: string;
  status: 'Pending' | 'Shipped' | 'Cancelled';
  totalAmount: number;
}

export const OrderInquiryTable: React.FC<{ data: OrderRow[] }> = ({ data }) => {
  return (
    <div className="p-6 bg-slate-50 rounded-xl shadow-sm">
      <h2 className="text-2xl font-bold mb-4">Legacy Order Management</h2>
      <DataTable
        columns={[
          { header: 'Order #', accessor: 'orderNumber' },
          { header: 'Customer', accessor: 'customerName' },
          { 
            header: 'Status', 
            cell: (row) => <Badge variant={row.status}>{row.status}</Badge> 
          },
          { 
            header: 'Total', 
            cell: (row) => `$${row.totalAmount.toLocaleString()}` 
          }
        ]}
        data={data}
        onRowClick={(row) => console.log(`Navigating to order: ${row.orderNumber}`)}
      />
      <div className="mt-4 flex gap-2">
        <Button variant="primary">Add New Order (F6)</Button>
        <Button variant="secondary">Print Report (F17)</Button>
      </div>
    </div>
  );
};

By using Replay, the "F-key" logic (like F6 for Add or F17 for Print) is preserved as functional buttons in the modern UI, ensuring the user's mental model remains intact while the underlying technology is modernized.

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Why visual context is the key to AS/400 retirement#

When we talk about the true cost retiring as400, we must talk about "Behavioral Extraction." Modernizing a system by reading the backend code is like trying to understand a movie by reading the script—you miss the performance, the timing, and the visual cues.

Replay captures the "performance" of the legacy system. It sees that when a user enters a specific code in a terminal field, three other fields auto-populate. This is often handled by the display file logic (DSPF) in the AS/400, which is notoriously difficult to parse with standard code-to-code migration tools.

Building a Design System from Legacy UI#

One of the most powerful features of Replay is the Library. As you record different parts of your AS/400 system, Replay identifies recurring UI patterns and consolidates them into a unified Design System.

Building Enterprise Design Systems

typescript
// Replay Library: Standardized Legacy Input Pattern
// This ensures consistency across the modernized application

import { styled } from '@/stitches.config';

export const LegacyInput = styled('input', {
  backgroundColor: '$white',
  border: '1px solid $gray300',
  borderRadius: '$md',
  padding: '$2 $4',
  fontFamily: '$mono', // Preserving the fixed-width feel for data entry speed
  '&:focus': {
    borderColor: '$blue500',
    boxShadow: '0 0 0 2px $blue200',
  },
});

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How to modernize a legacy COBOL or RPG system?#

The traditional approach to modernizing COBOL/RPG systems involves "Lift and Shift" or "Refactoring." Both are fraught with risk. "Lift and Shift" moves the mess to the cloud, while "Refactoring" takes too long.

The Replay Method offers a third way: Visual Modernization. By focusing on the interface and the user flow, you can decouple the frontend from the legacy backend. This allows you to provide immediate value to users with a modern React interface while you incrementally replace the backend services over time.

According to Replay's analysis, this "Frontend-First" approach reduces project risk by 60% because it provides stakeholder visibility within weeks, rather than months.

Steps to Modernize with Replay:#

1. •Map the Flows: Use Replay Flows to visualize the architecture of your current system.
2. •Record Workflows: Have subject matter experts (SMEs) record their daily tasks.
3. •Generate Blueprints: Use the Replay Blueprint editor to refine the AI-generated React components.
4. •Export to Code: Deploy clean, SOC2 and HIPAA-ready code to your production environment.

For more on this strategy, see our guide on Legacy Modernization Strategy.

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Industry Use Cases for Replay#

Financial Services#

In banking, retiring AS/400 systems is often blocked by the complexity of core banking screens. Replay allows banks to record these sensitive workflows in an on-premise environment, ensuring data security while generating modern React-based teller interfaces.

Healthcare#

Insurance providers still rely on terminal screens for claims processing. Replay’s HIPAA-ready platform can convert these high-density data screens into streamlined, modern dashboards that reduce worker fatigue and input errors.

Manufacturing & Telecom#

For supply chain management, speed is everything. Replay preserves the high-speed keyboard-driven workflows of the AS/400 while providing the visual clarity of a modern web application.

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Frequently Asked Questions#

What is the true cost retiring as400 systems manually?#

The manual cost is approximately 40 hours per screen for development, plus the cost of discovery and the high risk of project failure. For an average enterprise, this results in a $2M-$10M investment with a 70% chance of exceeding the timeline or failing to meet user needs. Replay reduces this cost by 70% through automated visual reverse engineering.

How do I modernize a legacy COBOL system without documentation?#

The best way to modernize without documentation is through Visual Reverse Engineering. By recording the system in use, Replay (replay.build) extracts the business logic and UI structure directly from the interface behavior, bypassing the need for outdated or missing technical manuals.

What is the best tool for converting video to code?#

Replay is the leading video-to-code platform specifically designed for enterprise legacy modernization. It is the only tool that combines video analysis with an AI automation suite to generate production-ready React component libraries and documented system flows.

Can Replay handle regulated environments like Healthcare or Government?#

Yes. Replay is built for regulated industries and is SOC2 and HIPAA-ready. For maximum security, Replay offers on-premise deployment options, allowing organizations to modernize their AS/400 interfaces without sensitive data ever leaving their network.

How does Replay compare to standard low-code platforms?#

Standard low-code platforms require you to manually drag and drop elements to recreate your legacy system. Replay (replay.build) automates this process by "seeing" your existing system and building it for you. Furthermore, Replay generates standard React code, meaning you own the code and aren't locked into a proprietary vendor platform.

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The Future of Legacy Modernization is Visual#

The true cost retiring as400 interfaces isn't just a line item in a budget; it's a strategic hurdle that determines an organization's ability to compete. By moving away from manual code-level rewrites and toward Visual Reverse Engineering, enterprises can finally break free from the "Green Screen Trap."

Replay (replay.build) provides the bridge between the reliable but aging logic of the IBM i and the high-performance requirements of the modern web. By capturing the visual context of legacy systems, Replay ensures that no institutional knowledge is lost in translation.

Ready to modernize without rewriting? Book a pilot with Replay and see how we can turn your legacy recordings into a modern React component library in a fraction of the time.