System Software and Operating Systems

Chapter 8 in Discovering Computers 2000 (Shelley, Cashman

and Vermaat)

Hardware vs. Software

Hardware consists of the parts of the computer you can touch– keyboard, mouse, monitor, printer, drives,

motherboard, CPU and so on

Software is simply a set of instructions (a.k.a. a program), it tells the hardware what to do and when to do it

Software within Hardware

While the software (the instructions) are stored on chips or disks, it is distinct from them

Analogy: in the same way that a musical score is distinct from the paper it’s printed on or the CD recording of it

Hardware is the part of the computer you can kick; if you can only curse at it it’s software

Interface

An “interface” is a boundary or region of contact between two entities and typically where any interaction or exchange takes place

The interface between the user and hardware is multi-layered

There are interfaces within interfaces

The various levels

The layer closest to the user consists of “application packages” (like Word, Excel and PowerPoint) that help the user perform particular tasks and high-level languages (like C, Basic, Pascal, Fortran, etc.)

the layer closest to the software is called the BIOS (Basic Input/Output System)

In between lies the “operating system”

BIOS

The BIOS is a set of instructions stored on a read-only memory (ROM) chip

It is sometimes called “firmware” since it occupies the middle ground between software and hardware. (The instructions are built right into the chip.)

You may see the term BIOS on the screen soon after you turn on the power

BIOS (cont.)

It checks on (detects) the other parts: memory, keyboard, mouse and so on

Then it looks for the “boot program” that will load the operating system

It always looks to the floppy disk drive first, which is why you shouldn’t have a floppy in the drive when you are booting the system

BIOS (cont.)

While it is most noticeable during the boot process, the BIOS is used constantly

This separation of BIOS from operating system allows for changes in hardware without a major rewriting of the operating system software

Device Drivers

If one has a new piece of hardware, the interface instructions connecting it and the operating system may not be written into the system’s ROM chip, the software (as opposed to firmware) is needed

This software is called a “device driver”

The Vast In-Between

Between the high-level (user friendly) applications and the BIOS is the “system software,” most notably the operating system but also language translators and utilities

The operating system consists of programs for loading and executing applications, storing or retrieving files, managing the CPU, switching between tasks and so on

Utilities

File Viewer: shows you the file or part thereof, esp. if it’s a graphic file

File Conversion: takes in one format and it into a another

File Compression: shrinks the size of stored files

Backup: makes a copy of your files in case of a system crash

Utilities (Cont.)

Diagnostics: are things installed and working properly?

Uninstaller: gets rid of applications you no longer want

Anti-virus: seek and destroy virus, protection too Screen Saver: it used to be that it literally saved

the screen, now mostly entertainment, sometimes security

Utilities and Language Translator

Desktop Enhancer: organizes desktop Internet manager: manage your website LANGUAGE TRANSLATOR: takes a

programmer’s high-level code and converts it to a binary code that computer components “understand.” (Again this is done in several stages.)

Op. Sys. Types of Interfaces

Command-line interface: the user types keywords (commands) after a prompt

Menu-driven interface: the user selects options from a menu typically using the arrow and Enter keys

Graphical User Interface (GUI): the user points to icons with the mouse, etc.

The kernel

Especially with GUI interfaces, operating systems have become rather large

Once the boot program is loaded into memory, it in turn loads the essential parts and the more frequently used commands (the kernel) of the operating system

The rest (the external commands) are loaded only when needed

Multi-this, Multi-that

Operating systems may be distinguished in whether they allow – multi-tasking– multi-threading– multi-users– multi-processors

Multi-tasking

A task or process is a program or part of a program the user wants executed

Modern operating systems are multi-tasking in that they execute two or more applications running simultaneously (actually they switch back and forth between the applications)

Older single-tasking operating systems could only do one thing at a time

Types of multi-tasking

context switching: only one process is active, but the status of the other process is preserved

cooperative multitasking: switching occurs at natural breaks in the process, but one application can take over

preemptive multi-tasking: tasks are prioritized and looked in on often so that one of them does not monopolize the CPU

Multi-threading and Multi-user

Multi-threading: similar to multi-tasking but takes place within a single application, e.g. one wants to take in typed information and see it on the screen simultaneously

Multi-user: having more than one user, operating systems for work stations, mainframe, mini and supercomputers allow for more than one user

Multi-processor

If a single CPU is insufficient for your computing purposes, you may need an operating system which can coordinate a number of CPU’s (processors)

asymmetric: different tasks assigned to different CPU’s each with its own memory

symmetric: tasks and memory shared equally among CPU’s

System Management

The operating system – manages the processes– manages the memory

• temporary storage (e.g. buffers)

• more permanent (e.g. disks)

– manages input and output– manages security– monitors performance

Proprietary vs. Portable

An important distinction in the business life of an operating system– Proprietary: limited to a specific vendor or

computer model, marries software to specific company’s hardware

– Portable: will run on many different systems one can change hardware companies without changing software companies

Some Operating Systems

MS-DOS (Microsoft Disk Operating System)

Windows 3.0 and 3.1 Windows 95 Windows 98 Windows NT

Some more OP’s

Macintosh OS/2 UNIX NetWare