WHY MAINFRAME?

An obsolete device still used by thousands of obsolete companies serving billions of obsolete customers and making huge obsolete profits for their obsolete shareholders.

Introduction To Mainframes

Mainframe is an industry term for a large computer. The name comes from the way the machine is build up: all units (processing, communication etc.) were hung into a frame. Thus the main computer is build into a frame, therefore: Mainframe.

Mainframes have huge processing and storage capacity. The development cost involved with mainframes is also very huge and therefore mainframes are manufactured only by very large companies. Mainframe gets its usage and applications in banking and financial sectors where large-scale operation with millions of records per day is involved.

OS History

Characteristics of Mainframe

Multiprogramming and multiprocessing

 Mainframe is capable of multiprogramming, or executing many programs concurrently, and of multiprocessing, which is the simultaneous operation of two or more processors that share the various hardware resources.

z/OS makes multiprogramming possible by capturing and saving all the relevant information about the interrupted program before allowing another program to execute. When the interrupted program is ready to begin executing again, it can resume execution just where it left off. Multiprogramming allows z/OS to run thousands of programs simultaneously for users who might be working on different projects at different physical locations around the world.

z/OS can also perform multiprocessing, which is the simultaneous operation of two or more processors that share the various hardware resources, such as memory and external disk storage devices.

The techniques of multiprogramming and multiprocessing make z/OS ideally suited for processing workloads that require many input/output (I/O) operations. Typical mainframe workloads include long-running applications that write updates to millions of records in a database, and online applications for thousands of interactive users at any given time.

What is multiprocessing

Simultaneously running of serveral processors (CPUs) is multiprocessing.

What is non-partition able multiprocessor.

In multiprocessing all SPUs share one real storage and channels.

The operating sytem manages the processing; it assigns work to the first available CPU; in case the CPU failed, work is routed to another CPU. A single OS copy running on many CPUs with one real storage is Non-partition able multiprocessor.

Advantage of multiprocessor systems provided the backup capabilites for CPU failures. Also, the overall instruction processing rate increased because many cpus are available to execute instructions.

NON-PARTITIOABLE MULTIPROCESSOR.

System Control and Partition

Physically partition able multiprocessor

      In contrast to non partition able multiprocessors, physically partitionable multiprocessors have many CPUs with divided real storage and channels, running single image of the OS.

LOGICAL PARTITIONABLE MULTIPROCESSOR USING PR/SM

       Now, with OS/390, Logical partitioning of CPU with logical partitions of real storage and channel is adopted, using PR/SM ( Processor resources / system management ).  They run on different images of the same operating sytem or on different operating system.