IB Computing: 3.3 Operating Systems

Operating Systems

3.3.1 Operating system

3.3.2 Functions

3.3.4, 3.3.5 characteristics of various computer systems

Even Windows XP has a CLI - click run then type cmd in the box to open the command window. Typing help will give a list of OS commands. It's actually faster to do operations like copying files via this interface rather than the standard Windows Explorer.

This description will go out of date very quickly - especially in terms of RAM, CPU speed and backing store of the "typical" pc.

On this page: [ Basic nature | OS core functions | Characteristics | Types of computer ]

Basics

A computer is a machine , composed of various bits of hardware . Early computers had to be operated directly with switches and cables which connected one component to another. Clearly, this limits the speed and operability of the machine.

Core functions

Operating systems provide core functions and a suite of utilities which provide services such as formatting floppy discs, creating backup file sets or transferring data from one file format to another. Operating systems also provide a user interface and control the running of applications programs. An operating system also controls the startup or "booting" of the system.

Operating systems operate with typed in commands (requiring command-line interpreters or CLI's) while later ones have developed graphical user interfaces (GUI 's). Many systems offer both.

A Summary of OS Functions:

. Access control (who can do what, who is on the system and when)
. Accounting (of resources used and by whom)
. Error handling
. I/O handling
. Interrupt handling
. Job Sequencing (jobs - running programs - can have different "priorities")
. Protection and security
. Provision of operator/user interface(s)
. Resource allocation (eg of peripherals)
. Memory management
. Resource allocation (eg of peripherals)

Characteristics of computer systems

One characteristic of a computer system is the number of users it can handle at one time. We are mostly used to single-user systems such as our trusty pc or laptop. However, mainframe and mini-systems have multiple workstations or terminals so that many people can use the same system at the same time - multi-user systems.

Another is the number of processes or tasks that can be run at the same time. Most computer systems today are multi-tasking rather than single-tasking as older personal computers were. Larger systems like mainframes have always been capable of multi-programming - running more than one computer program at a time.

Types of computer system

Type	Hardware	Other characteristics
Personal computers (pc's)	The desktop pc (or microcomputer) typically has 128-512 Mb of RAM (primary memory), 40 - 80 Gb of Backing Store, a CD or DVD drive (secondary memories), keyboard, mouse and monitor.	Multi-tasking (can apparently run many different tasks at the same time by allocating each one a small amount of CPU time. Single user, often found in schools and offices. Cost is around USD 2000 or less. Typically based around microprocessors with a 32-bit word and operating in the 1-2 GHz range.
Portable Computers	More or less the same but runs on batteries with a life of, typically 2 - 6 hours. Many will have low-power versions of standard microprocessors. Some may do without CD ROM to save space and weight.	Favoured by people who need to compute or communicate on the move. Frequently used by business people who need to access their company computer via modem and "virtual private network" - for example to record new sales or check on developments. Growing popular in classrooms too. Typically costs around 50-75% more than an equivalent pc
Mainframe computers	A whole other kind of computer, this is a very powerful machine of quite large size which needs a special operating room of its own. A typical modern mainframe (the IBM S/390 - Generation 5 Server (S/390 G5) "can perform at more than 900 MIPS (Million Instructions Per Second) when configured with 10 microprocessors". These systems often use "disk farms" for storage in the TByte range.	I'm not sure of the cost of a mainframe but let's say you could easily spend USD 1,000,000 equipping your enterprise with a mainframe system. These systems are multi-user systems which typically support 100's of simultaneous users with no appreciable degrading in the apparent speed at which they operate. Mainframes would be found in banks, insurance companies, supermarkets and supermarket chains, ISP's and telecommunications companies. A typical mainframe computer would have a 64-bit word length and associated buses.
Supercomputers	The most powerful computers money can buy and they increase in power and speed with each brand new purpose designed system (you don't buy one of these off the shelf in your local computer megastore). In terms of speed and storage, the US Weather Bureau ordered one a couple of years ago running at around 50,000 MIPS with 4 GBytes of primary memory and 4 TBytes of secondary memory.	Usually used for dedicated applications - some of which we mentioned at the end of the previous section . Price - if you have to ask you can't afford one - lets say USD 10,000,000. Although they have the potential to be used by 1000's of people at the same time they are usually used in applications which require billions or even trillions of calculations to be performed. If you imagine that the weather simulation is performing a dozen calculations for each 1 km cube of the atmosphere above the Continental USA that's a significant amount of number crunching. A supercomputer may well use a 128-bit word length.

related: [ Common core home | previous: peripherals | next: processing ]

These days a computer, be it a pc or a supercomputer , comes with a set of programs which interact with the hardware. This is the operating system which is used both by users and by other applications running on the computer.

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