Transcript System Software and Operating Systems

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