Mainframe Introduction

In this Mainframe tutorial you will learn about mainframes and its concepts and some of the early mainframes describing the evolution and history of mainframes in detail. History and Evolution of Mainframes, Mainframe Channel, Direct Access Storage Device – DASD and Logical Partition – LPAR.

What is Mainframe?

As we all know the term mainframe when said to a layman would give a feeling of a large computer, but the question arise how large it is and what is the specialty of these mainframes. The answer to this question lies in the term "Mainframe" itself.

As the name implies mainframe is the main computer with all units processing, communications are built into a frame and hence the name Mainframe, which thereby denotes a very large computer.

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.

Apart from the above there is also enterprise class mainframe integration which has greater features and ability of connecting mainframe data sources to distributed platforms. Thus, with specific, specialized and powerful features of mainframes like security, high performance, reliability, scalability and manageability are achieved and provided to distributed applications using mainframe resources.

History and Evolution of Mainframes:

Some of the early mainframes which were developed starting from the year of 1942 are ENIAC, MARK1, BINAC, UNIVAC. ENIAC is also called as electronic numerical integrator and calculator was developed in the year 1942. This mainframe machine weighed in tones and consumed enormous electric power. It had thousands of vacuum tubes, relays resistors, capacitors, and inductors inside it.

In the year 1951, UNIVAC-I was developed specially for the US Census Bureau. The major difference between UNIVAC and ENIAC was the processing of digits. In UNIVAC, processing was done in serial mode, yet the speed of UNIVAC was higher than ENIAC with one disadvantage of vacuum tubes generating enormous amount of heat which made the mandatory requirement of a large good air conditioning system.

Later in 1954, Univac II was developed. In 1962, the concept of virtual memory, a powerful feature which shall be discussed in later sections, was introduced in mainframes making the system even more powerful.

In 1964, the first third generation computer named as Burroughs B5000 came into market. This mainframe system had various powerful specialized features like multiprogramming, multiprocessing and virtual memory.

Later on various improved versions of Burroughs series came into market with new features in each. Among this the most notable one was B6700 which came in the year 1971 and this supported the feature of dynamic linking of programs at runtime.

IBM was producing and releasing mainframes in the market at all periods from past till present with the successive development of IBM Series starting with System/360.

One of the biggest factors associated with mainframes is its huge cost which made its usage only possible for big companies and corporate. There are still many technical terms one must get familiarized with mainframe systems to understand about mainframe systems in depth.

Let us see some of the internal technical usage of mainframe system.

Mainframe Channel:

A mainframe channel connect to one or more controllers via either pairs of large "bus and tag" cables or, fiber optic ESCON (Enterprise System CONnection) cables and FICON, which has the ability controlling one or more devices. This is one of the important term in mainframe technology since it has the ability of take care of huge input and output functions.

DASD:

DASD stands for Direct Access Storage Device. This indicates to any type of storage that was directly (randomly) addressable.

LPAR:

LPAR stands for Logical Partition and is a powerful hardware or firmware feature implemented in all mainframe systems. By this feature it is possible to create partitions and by which CPUs and I/O sub-systems can be shared between logical partitions.

A emaulator program or application, like a telnet, takes the responsibility of emaulating the terminal meaning that the commands typed in the terminal would be sent to the mainframe system for processing and the results from the mainframe system is sent back to the terminal for the user’s display. This concept is done by opening sessions and connecting to the mainframe system though the emaulator application. The user in the mainframe gets into the mainframe session by using the userid and password which is unique for each user of the mainframe system. Thus, it is possible in a mainframe system for the users to interact and communicate by means of terminals in the environment though the actual mainframe system is located elsewhere.