ch 5; 1-10 Flashcards
System Software
- Application software: “High level” software that performs a useful task for the user
- System software: “Low level” software that makes the computer run
=Operating System (OS)
=Device Drivers
=Utilities
Operating System
-Low-level software that controls the computer hardware
=Manages Hardware
==Hides the complexity of the hardware from the user.
==Tasks that would be extremely difficult (such as saving a file) become simple (for the user).
=Provides a user interface.
=Manages system resources, such as the CPU, memory, storage devices, etc.
=Communicates with peripheral devices through device drivers.
User Interface (UI)
-Determines how the user interacts with the computer.
-Command-line user interface
=Older type of UI
=Instructions must be typed in
-Graphical user interface (GUI)
=Newer type of UI
=Lets user point and click on graphic objects such as icons and buttons
Easier to use than command-line UI
Managing the Processor
-Single-tasking versus multi-tasking
-In a single-tasking OS, only one program can be executed at a time.
-In a multi-tasking OS, multiple programs can be executed at the same time.
=CPU can only be executing instructions from one program at a time.
=OS causes CPU to rapidly switch between programs, giving the illusion that all are running simultaneously.
=This switching normally happens thousand of times a second
Managing Memory (RAM)
-The OS manages the memory for all programs and data files.
-All programs executed and data files opened are loaded into separate areas in memory.
-These memory areas should never overlap one another.
-If there is an error with memory management, computer usually crashes:
=Blue screen of death (Windows)
=Grey screen of death (MacOSX)
-What happens if not enough memory to hold all programs and data?
Virtual Memory (Not in Book)
-Allows users to open up more applications and data files than can physically fit in the computer’s memory (RAM).
-A special file on the main storage device, called a swap file, is created.
-When not enough room in memory, some content is copied to the swap file to free up space (a process known as paging).
-When content currently in swap file needs to be accessed, it is copied back to memory (likely causing other content in memory to be copied to swap file).
-Paging slows down the system… if it happens too frequently, computer can become totally unresponsive (thrashing).
Managing System Resources
-Ensures only one process at a time can access a hardware device.
-Example: Multiple print jobs
=A printer cannot print multiple docs at a time, so for each print request, the OS sees if the printer is in use. If it is not, the print request (job) is sent to the printer immediately, otherwise it is put in a queue. As each print job finishes, the OS checks the queue and sends the next job to the printer.
-Access to other hardware (hard drives, etc.) work in a similar manner.
Peripheral Devices
-Operating system has to communicate with printers and other peripheral devices that may be plugged into the computer.
-Small programs known as device drivers are used for this.
-Device drivers written by company that creates the hardware.
-Acts as a translator… translates instructions from the OS to format the device understands.
-PnP (Plug-and-Play): Ability for the OS to recognize when a new device has been plugged in… it determines the device driver needed and automatically installs it if possible.
APIs
-Stands for Application Programming Interface
-Allows application programs to call API functions to have the operating system perform low-level tasks such as saving a file to a storage device.
-Makes writing software easier since programmers do not need to know hardware details.
Desktop Operating Systems
MS-Windows
Mac OSX
Linux
