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1. IBM Z COMPONENTS
The z/OS operation system manages the IBM Z hardware, together used in the biggest businesses and governments worldwide to handle critical data. Such system must operate 24/7 on all days of the years. Built to have zero downtime.
The system is designed for mixed work where many tasks are running at once coming from millions of requests.
FIGURE OF IBM Z LOGIC STRUCTURE:
Started Task: can be started and made immediately available to batch tasks and real-time transaction tasks; for long-running critical applications. Control over where and when the job control language (JCL) is run (e.g. a JCL is started at each initial program load (IPL) of the system).
2. OPERATING SYSTEM SERVICE TASKS
A traffic coordinator for huge amount of physical resources (disk storage devices, network connections, processors and memory).
The IBM Z system is designed for input and output (I/O) throughput.
3. REAL-TIME TRANSACTION TASKS
Interactive and typically involve a relatively small amount of input to quickly return a result. The entire I/O round trip of a transaction is much less than a millisecond:
load the appropriate program
get data requested by the program from the IBM Z managed physical resources
send result to the requesting application or users
Generally Started Tasks initiated when the operating system starts, IPLs, ready to receive requests, immediately process the request, and return the result. Typical example is: credit card reading on a terminal upon payment.
4. REAL-TIME TRANSACTION SYSTEMS
Customer Information Control System (IBM CICS): real-time transaction processor started task. A single z/OS operating system can concurrently run hundreds of CICS started tasks called regions where each CICS is concurrently processes many transactions.
These transactions are the actions and updates resulting from messages sent to a CICS application program.
In 2026, CICS can proces 1.1 million transactions per second - that's 100 billion per day.
Insurance companies use CICS to manage claims, travel companies use CICS to manage reservations and banks use CICS to track things like their clients’ deposits and withdrawals.
Information Management System (IBM IMS): z/OS real-time transaction processing and data base transaction processing.
In 2026, IMS can process 21,000 transactions per second - over 1 billion per day.
UNIX System Services (IBM z/OS USS): a real-time started task providing a UNIX-certified file and process environment through Transmission Control Protocol (TCP) applications (e.g. Secure Shell (SSH), File Transfer Protocol (FTP), any TCP socket application processing).
IMB DB2 Family: real-time transaction started task managing a relational data base data source used by other transaction systems such as CICS, IMS, USS, time sharing option (TSO) and message queue (MQ).
IBM MQ: a message delivery real-time transaction started task. It simplified business application programming by eliminating the need for verification of data sending from other business application programs, regardless of the computer hardware and operating systems.
Used with e.g. bank ATMs, hospital admissions, retail point of sales (POS), IBM business partners large-scale computer systems.
Time Share Option (TSO): a classic interactive system from before the internet and browsers, used today as well by programmers and administrators.
The Z mainframe has other OSs like as IBM z/TPF Transaction Processing Facility and IBM z/VSE, with other real-time transaction started tasks.
5. BATCH TASKS
Batch tasks are equal with batch jobs.
Used for bulk processing of data from real-time transactions. A submitted task workload for the system to complete in the background. It's best for processing a massive amount of data records (e.g. a major retail company processing its daily inventory).
Also, a sequence of activities, job steps, for which no user interaction is needed.
The z/OS typically processes many batch jobs while concurrently processing many real-time transactions.
A real-time system started task, IBM Job Entry Subsystem (JES), is responsible of accepting submitted batch work, scheduling the work according to a variety of priorities and managing the batch output.
6. IBM Z/OS MAJOR SOFTWARE COMPONENTS
Crypto Services
Workload Managers (WLM/IRD)
Job Output (SDSF)
Job Management (JES)
Software Maintenance (SMP/E)
SNA (TCP/IP)
Performance Monitoring (RMF)
Activity Reporting (SMF)
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