LARGE SYSTEM OVERVIEW (LSO)

LSO
Large system overview
Computer: It is an electronic device which accepts some data as input and produces some processed data.
The processed data is called as information.

Operating Systems:
Software that controls a computer and acts as a layer between the hardware and the applications and users. (e.g. Linux, Windows, Mac OS X, UNIX)

Program: A set of instructions to perform a particular task

Evolution of computers:

1. Microcomputers
2. Minicomputers
3. Mainframes
4. Supercomputers

Microcomputers: A computer which has microprocessor as a chip is called as microprocessor
It is single user oriented. It is a single-processor system


Ex: pc, desktop, notepad
Operating systems: windows, Linux

Minicomputers: Medium-capacity computer that is larger than a microcomputer but smaller than most mainframes.
We can say it as smaller versions of mainframes.
A minicomputer can handle a larger amount of data than a microcomputer and can perform most of the functions of a mainframe

Operating systems: AS/400, Portable UNIX

Mainframe:
It is a large computer capable of handling huge amount of data at high speed and provides good security.
It is oldest form of computer.
It is very Expensive and powerful.
It is a multiprocessor system
It is multiuser oriented
Note: It contains 250 GB capacity of RAM; It processes 750 MIPS (Million Instructions Per Second).

Operating Systems
Dos, OS/VS1, OS/VS2, MVS-XA, MVS-ESA, OS-390, Z/OS

Features of Mainframes
It is a very powerful computer,
High speed storage, it can store large volume of data at high speed.
Computing speed is very high, it can process large amount of data at high speed
Multi-user, multiple users can access server at a time
High data bandwidth


Applications
Banking sector
Insurance
Railways
Retails market
Manufacturing


Super Computers
A supercomputer is a computer that performs at or near the currently highest operational rate for computers.
A supercomputer is typically used for scientific and engineering applications that must handle very large databases or do a great amount of computation
It is equalent to 50,000 pc

Evolution of IBM Mainframes Systems

System/360: It is developed in 1964, Dos was the operating system, 8bit processor, single processor & single user oriented. Only one program can execute at a time.

System/370: Introduced in 1970, computing speed is very higher than system/360, 16bit addressing mode, Os/vs1 & Os/vs2 are the operating systems, Virtual storage concept has been introduced.

System/370XA: It is introduced in 1980, 24bit processor, it introduces MVS concept, Os are MVS/XA & MVS/ESA, It is dual processor.

System 390: It is introduced in 1994, it is a 32 bit processor, Multi-user oriented and Multiprocessor, It is enterprise server, Os/390, Z/OS (64 bit processor).

Architecture of mainframe computer:

1. C.P.C 2. Main Memory 3. DASD 4. I/O Channel

INPUT OUTPUT CHANNELS





C.P.C
MAIN MEMORY


DASD
(SECONDARY MEMORY)















C.P.C: Central Process Controller, mainframe can have up to 32 processors

Main Memory: It is a real storage between DASD and processer. The data that is to be processed will be first loaded into main memory for faster retrieval.

DASD: Direct Access Storage Device. All the data user programs, system programs are stored in DASD

DASD is divided into units and units into volumes, volumes into cylinders, cylinders into trackss, tracks into blocks
15 Tracks = 1 cylinder
6 blocks = 1 track
28 cylinders = 3 unit
1 track = 192KB or196608 bytes, 1 block = 32 KB

I/O Channel: It is a special type of processer which is used to send the data from DASD to main memory.

Evolution of IBM Mainframes Operating Systems

OS/VS1: It is introduced in 1972 for System 370 server; It works on Virtual Storage Concept
OS/VS2: It is introduced in 1974 for System 370/XA, It works on Multiple Virtual Storage concept.
MVS/XA: It is extended architecture, introduced in 1983; it works on 24bit addressing mode, MVS concept.
MVS/ESA: It is introduced in 1988 for System 370/XA, It is completely Enterprise service architecture, 32 bit addressing mode.
OS/390: It is introduced in 1996 for System 390, 32 bit addressing mode
Z/OS: It is zero down time operating system introduced in 2000 System 390, it is a 64 bit addressing mode,


Characteristic Features of Mainframes Operating Systems

1. Virtual Storage
2. Multiple virtual storage
3. Multi-programming
4. Spooling
5. Batch process
6. Online process


Virtual storage: It is a technique that lets processer to assume an amount of main memory that is larger than real memory.
The virtual memory is divided into pages of 4KB
The real memory is divided into frames of 4KB
The auxiliary or secondary memory is divided into slots

Actually the processer can execute only one instruction of a program at a time. So only that instruction needs to be presence in the real storage. the operating system divides program into smaller pages of 4KB and transfer only active portion of program to real memory after executing the instruction the instruction will send back to secondary memory at the same time next instruction will be retrived.this swapping will be done by OS.
Multiple virtual storage: Using this concept the multiple programs will be executing at the same time. Operating system creates infinite virtual storages so that multiple programs can use the multiple address spaces to get execute.
Multi programming: More than one program executing at the same time.
Actually the processor can execute only one program at a time, but in multi programming more than one program can have the control of C.P.U. for example if a program has to read data from a file the processer has to wait for I/O channel. During this waiting state another program can have the control of C.P.U. like wise multiple programs can have the control of processer.
Spooling: The method of putting programs and inputs in a batch and queuing the outputs is called as spooling.
In multiprogramming multiple jobs will be submitting. All these programs will be put in an input queue. This will be done by I/O processer. After executing all the programs the output will be sent to the output queue again which will be taken care by I/O processer. After then the output will be send to output queue.

Batch processing: The process of executing multiple jobs at a sequence with out user interaction is called as batch process where one job contains multiple programs. A bulk amount of input will be given to get bulk amount of output.
Online process: The process of executing a program where user interaction is necessary. Single input and single output.
Resource access control facility (RACF): It is a component which gives security to the mainframes server.
The RACF administrator will create user profiles, passwords and resource profiles.
Administrator will give authorization to user’s to access resources.
RACF will acquire all the user id’s and passwords’.
Each time the user login and accessing the resources the authorization will be checked weather the user is authorized to use the resources