Date post: | 27-Dec-2015 |
Category: |
Documents |
Upload: | rodger-poole |
View: | 219 times |
Download: | 1 times |
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