Mainframes

Advantages of Mainframe Computers

✦ Availbility

➤ The recent mainframe systems Z series are designed to provide availability of 99.999%.


✦ Scalability

➤ The ability of a system to expand as resources, such as processors, memory, or storage are deleted.


✦ Reliability

➤ It is a measurement of the ability of a system to continue processing without failure.

➤ The "Z" in the system Z's brand name stands for Zero down-time.

➤ System Z servers have reported a 'Mean Time to failure' of 40 years, which means they are guaranteed to run
continuously for 40 years without any failure.


✦ Compatibility

➤ Programs written for the IBM OS/360 and later models will still run quite happily on the latest version
of IBM Z/OS, usually without even a recompile or re-assembly (that's nearly 50 years of continuous upward compatibility
and reliability).

➤ IBM has been maintaining downward compatibility for every new release of hardware and software.


✦ Redundancy

➤ One of the most obvious benefits of the mainframe environment is the incredible amount of redundancy
that the mainframe features.

➤ It is the use of several identical functional units, such as several disk drives or power supply systems,
within one computer system in order to provide data security and a certain degree of fault tolerance in case of
hardware failures.

➤ Redundancy power supplies, processors and storage devices create a system that practically can't be taken offline.


✦ Customization

➤ Mainframes are able to be completely customized to fit an individual user's need.

➤ The mainframes is built to order by ibm and thoroughly tested to ensure that it meets customer requirements.

➤ Individual processors can be turned on and off on real-time needs, and operating parameters are completely customizable.

➤ Additionally, it is possible to run multiple operating systems or Z/OS instances on multiple logical partitions at the same time.

➤ Additionally, most large companies have applications developed or customized to specially meet unique business needs.

➤ Estimates that up to 70 % or percentage of corporate production data still resides on the mainframe.

➤ This means that private clouds residing on system Z have secure access to essential information that can be shared if necessary
with adequate access controls, encryption, data security, data masking and integrity.


✦ Security

➤ Modern mainframes have security built into them from the ground up, both in the operating system and through
cryptographic hardware acceleration.

➤ Governments, Univerisities and large-scale enterprises like banks, insurance companies.. etc.

➤ All of whom have a critical requirement to keep user and internal data protected at once protected but also highly retrievable.

➤ At the kind of high-demand loads we talked about in the first point, you will begin to see the daunting nature of that task
when you realize, for example, that all of those hundreds of thousands of requests that VISA processes every second have to be both
encrypted and decrypted in real-time.

➤ I.E., At a speed that won't be noticeable to those hundreds of thousands of simultaneous users.

➤ It's a task that lower-powered servers aren't quite up to - but one which built-in hardware acceleration of
the encryption and decryption processes help the mainframe excel at.

➤ There is not a single incident of virus or worm or spyware or malware attack in the last 50 years history of a mainframe.

➤ The power of IBM's Z system processor can move mountains of data, billions of instructions and supports
parallel processing.

➤ A batch job that copies billions of records from one file to another file structure can take minutes instead of hours.

➤ Multiprocessing of hundreds of simultaneous users, system tasks, online service and batch jobs will not crash a processor:
a mainframe LPAR image is designed to handle heavy loads.

➤ The processor will not crash from overuse or overheating like ordinary computers.

➤ The latest Z13 mainframe uses the most powerful processor on the planet. The Z13 supports up to 8000 Linux
images simultaneously for cloud computing.

➤ For the mobile economy the Z13 does real-time encryption and can process 2.5 billion transactions per day.



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Characteristics Features of Mainframe Operating System

♨ Virtual Storage:

In most computer systems, the processor's main storage is among the most valuable of the systems resources.

As a result, modern mainframe computer operating systems provide sophisticated services to make the best use of the available main storage.

Among the most important of these services is virtual storage.

Virtual storage is a technique that lets a processor simulate an amount of main storage that is larger than the actual amount of real storage.

For example, a processor that has 2M bytes of real storage might use virtual storage to simulate 16M bytes of main storage.

To do this, the computer uses disk storage as an extension of real storage

The key to understanding virtual storage is realizing that at any given moment, only the current program instruction and
the data it accesses need to be in real storage. Other data and instructions can be placed temporarily on disk storage,
and recalled into main storage when needed.

In other words, virtual storage operating systems transfer data and instructions between real storage and disk storage as they are needed.

Although the details of how an operating system implements virtual storage varies from one system to the next, the basic concept is the same.

Fortunately, virtual storage is largely trans-parent from the users point of view, virtual storage appears to be real storage.


♨ Multiprogramming:

Multiprogramming means that the computer lets more than one program execute at the same time, i.e., at any given moment, only one program can have control of the CPU.

Some processing operations like reading data from an input device - take much longer than others.

As a result, most programs that run on mainframe computers are idle a large percentage of the time, waiting for I/O operations to complete.

If programs were run one at a time on a mainframe computer, the CPU would spend most of its time waiting.

Multiprogramming simply reclaims the CPU during these idle periods and lets another program execute.

♨ Spooling:

It means Simultaneous Peripherals Operations On Line.

A significant problem which must be overcome by multiprogramming systems is sharing access to input and output devices for the programs that execute together.

For example, if two programs executing at the same time try to write output to a printer, the output from both programs is intermixed in the printout.

One way to avoid this problem is to give one of the programs complete control of the printer, which defeats the purpose of multi programming because the other program has to wait until the printer is available.

To provide shared access to printer devices, spooling is used.

Spooling manages printer output for applications by intercepting printer output and directing it to a disk device instead.

When the program finishes, the operating system collects its spooled print output and directs it to the printer.

In a multiprogramming environment, the operating system stores the spooled output separately on the disk so that it can print each programs output separately.

♨ Batch Processing:

A batch file contains a series of commands that are processed together as a batch.

In batch processing multiple programs are processed (works is processed) in units called jobs. Jobs are submitted in batch and
will be executed in sequence.

The data will be provided along with job so no user interaction will take place.

One of the problems that arise when batch processing is used is managing how work flows through the system.

To manage this in the multi-user system, the Job Entry Subsystem (JES) processes each users job in an orderly fashion.

♨ Time Sharing:

It is the another feature of MVS in each each job will be alloted with certain piece of job and each user feels as CPU time is alloted
for it only.

In a time-sharing system, each user has access to the system through a terminal device.

Instead of submitting jobs that are scheduled for later execution, the user enters commands that are processed immediately.

Hence this is sometimes called "Interactive Processing", as it allows users to interact directly with the computer.

Time-share processing is called "Foreground Processing" and batch job processing is called "Background Processing".


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Evolution Of Z / OS (zero downtime operating system)

Primary Control Program(PCP):

➽ It was the first release of OS version by IBM in the year 1965. It had limited capabilities and it doesn't offer multi
programming, no priority scheduling and no spooling facility.

It was an unreliable system and became obsolete in the year 1969.

➽ Multiprogramming concept was introduced with the introduction of MFT and MVT.

MFT: Multi programming with fixed number of tasks.

MVT: Multiprogramming with variable number of tasks. It was the first reliable system and both MVT and MFT provide limited spooling
capability.

HASP(Houston Automatic Spooling Priority):

A group of IBM employees developed a package that is superimposed on MFT or MVT and provides good spooling capabilities.

ASP(Attached Support Processor):

It is another package developed for MVT that would allow several mainframes to work together under one operating system
in a master or slave relationship.

OS/VS OR System/370:

In this virtual storage capabilities were provided and new hardware VS1 and VS2.

VS1 was basically an MFT system in a virtual environment. VS2 has two versions SVS(Single Virtual Storage) and MVS (Multiple Virtual Storage)

➽ In 1987 only MVS was left behind and MVS along with HAS was named as JES2(Job entry subsystem) and MVS along with ASP was named as JES3(Job entry subsystem).

➽ MVS provides reliability, integrity and performance. The only drawback was the limited virtual storage capability of 16 MB.

MVS / XA:(Multiple Virtual Storage or Extended Architecture)

It was a new version of MVS having storage availability of 2GB.

MVS / ESA:(Enterprise Systems Archittecture)

It was announced in 1988. In this virtual storage was extended upto 16TB.

Z / OS (zero downtime operating system)

It is the latest version.


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Introduction to Mainframes

Mainframe is a high performance multi user computer system which is the most scalable, available, reliable and
secure machine in the world capable of handling numerous terminals and peripherals simultaneously.

Terminal definition- A device, usually equipped with a keyboard and display device(Without a CPU), capable of sending and receiving information over a network. IBM 3270 terminals are used to connect to a mainframe computer.

A computer peripheral is any external device that provides input and output for the computer.

For example, a keyboard and mouse are input peripherals, while a monitor and printer are output peripherals.
Some peripherals, such as external hard drives, provide both input and output for the computer.

These are a type of computer that generally are known for their large size, amount of storage, processing power and high level of reliability. They are primarily used by large organizations for mission-critical applications requiring high volumes of data processing.

➤ It is the powerful central computer(CPU) in a data processing center,
linked to thousands of users through less powerful devices such as PC workstations or dumb terminals.
Usually you won't find a mainframe in any household or small companies.

➤ It is also referred to as "big iron"and it is used primarily by large organizations for critical applications;
bulk data processing, such as census, industry and consumer statistics, enterprise resource planning; and transaction processing.

➤ They are larger and have more processing power than some other classes of computers: minicomputers, servers, workstations,
and personal computers.

➤ The term originally referred to the large cabinets called "main frames" that housed the central processing unit and
main memory of early computers.

➤ Later, the term was used to distinguish high-end commercial machines from less powerful units.Most large-scale computer system architectures were established in the 1960s, but continue to evolve. Mainframe computers are often used as servers.

➤ In the mid-1950's, all computers are mainframes, since the term mainframe referred to the main CPU frame.

In those days, mainframe computers were not just the largest computers; they were the only computers. Several manufactures like IBM,
Honeywell, Burroughs produced main frame computers from the late 1950's. From 1970's the term mainframe computer
was almost synonymous with IBM products due to their market share.

➤ In the hierarchy of computers, mainframes are right below supercomputers, the most powerful computers in the world.
(which is why they are aptly named "supercomputers".)

➤ Yet a mainframe can usually execute many programs simultaneously at a high speed,whereas supercomputers are designed to
execute a single process at the highest speed.

➤ The ability of mainframes are often measured in Millions of instructions per second(MIPS) but supercomputers
are measured in floating point operations per second(FLOPS).

➤ Commonly supercomputers are used for scientific problems, while mainframes are used for business processing.

ZERO DOWNTIME Operating System-Z/OS-It is the latest version OS in Mainframes

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