Explain the difference between System/36, System/38, and AS400 (IBM i).

IBM developed the System/36 (S/36) and System/38 (S/38) as midrange computers in the late 1970s and early 1980s. The AS/400 (IBM i) was introduced in 1988 to unify and replace these systems while maintaining backward compatibility.

Feature	System/36 (S/36)	System/38 (S/38)	AS/400 (IBM i)
Release Year	1983	1979	1988 (IBM i continues today)
Target Audience	Small businesses	Mid-to-large enterprises	Businesses of all sizes
Operating System	SSP (System Support Program)	CPF (Control Program Facility)	OS/400 → IBM i
Architecture	16-bit, simple file system	48-bit, advanced database & security	48-bit (initially), later IBM Power
Database	Flat file-based	Relational-like, integrated DB	DB2 for i (fully relational)
Security	Basic user profiles	Object-based security model	Enhanced role-based security
Programming Languages	RPG II, COBOL, OCL	RPG III, COBOL, CL	RPG IV, COBOL, C, Java, SQL, PHP
User Interface	Green screen (5250 terminals)	Green screen (5250 terminals)	Green screen, Web UI, APIs
Virtualization	None	None	Logical Partitioning (LPAR), PowerVM

1. IBM System/36 (S/36) :

Designed for small-to-medium businesses with a focus on batch processing.
Used SSP (System Support Program) as its OS.
Emphasized ease of use with flat-file data storage (not fully relational).
Programming: RPG II, COBOL, and OCL (Operational Control Language).
Lacked advanced security and database management found in later systems.

* Strengths: Simple, cost-effective, and widely adopted in small businesses.
* Weaknesses: Lacked a modern database and security model.

2. IBM System/38 (S/38) :

Aimed at larger enterprises with a more sophisticated computing model.
Used CPF (Control Program Facility) OS with an object-based architecture.
Integrated an advanced relational-like database (precursor to DB2 for i).
Introduced security by design, with user-based and object-level access control.
Programming: RPG III, COBOL, and Control Language (CL).

* Strengths: Advanced security, integrated DB, and forward-looking architecture.
* Weaknesses: Expensive and complex compared to S/36.

3. IBM AS/400 (Now IBM i) :

Launched in 1988 as a successor to both System/36 and System/38.
Combined S/36's ease of use with S/38's advanced security and database.
Backward compatible with S/36 and S/38 applications.
Introduced OS/400, later rebranded as IBM i, with a fully integrated DB2.
Supports modern programming languages: RPG IV, SQL, Java, C, Python, PHP.
Advanced virtualization (LPAR) and cloud capabilities.

* Strengths: Scalable, secure, highly reliable, backward-compatible.
* Weaknesses: Perceived as outdated due to its green screen UI, but modernized significantly.