Operating Systems What do you have left on your computer after you strip away all of the games and application programs you bought and installed? Name some Operating Systems: Mac OS, Windows XP, MS DOS, UNIX, Linux

What is an operating system? The operating system: A collection of programs that manages and controls applications and other software, and coordinates the various hardware components to perform tasks requested by the user. Controls both Hardware and Software Allows use of (partial list!) the keyboard the mouse printing to a printer of your choice viewing information on a monitor saving or retrieving files formatting a disk running programs controlling any external device attached to the computer

History Loader: first program to become part of the Operating System The loader took care of loading object code (binary machine code) into memory Decide where to start loading Read first binary instruction, and store it in memory starting with the first place Add up to get the next spot Read in the second binary instruction, and store it in memory, etc When done, load the program counter with the starting address. And erase itself from memory. BUT: Programs ran one at a time. Later: How about stacking all jobs together? separator card, indicates where one job stops and the next began So a program was created to do job management and to load the next job each time it read the special indicator cards. Beginning of the operating system EXAMPLES: Mac OS, MS Windows, MS DOS, UNIX, Linux

BIOS BIOS (Basic Input Output System) Small unchangeable part of the operating system in the ROM. ROM: Read Only Memory retains instructions even without electricity – non-volatile RAM: Random Access Memory erased when power is off –volatile Start button  position 00000 of BIOS memory, begin executing. BIOS: BIOS loads the rest of operating system into RAM and turns control of the computer over to it. We say it Boots the System Bios is one of the pieces of the operating system BIOS is Also Also collection of programs that have the capability of communicating with peripheral devices. Keyboards, Disk drives, printers, display/monitors, and other devices. What is RAM = volatile - Read and Write memory, Random Access Memory. Volatile. No electric, no data What is ROM – not volatile. Read only memory. Permanently burned in. No electric, still have the instructions available.

Booting the Computer Load the OS Cold boot: Warm boot: Starting up the computer by turning the power on. Operating system in ROM looks for and loads the remaining operating system into RAM. Warm boot: Reloads the operating system into RAM without disrupting the power to the disk drives or power supply.

Some Tasks of OS Tasks of the OS Loads programs Does Job control (management) BIOS Device Drivers: special software that enables the computer to communicate with peripheral You can update the Operating System by adding a new device driver (for a new printer) Tasks Device Drivers: special software that enables the computer to communicate with peripheral devices Helps you communicate with computer’s hardware Acts as an assistant that moves jobs in and out of memory Helps in using keyboard, mouse, printing to printer Loading into RAM and starting up programs Change screen colors Use modems Manages files Multiprogramming: Allows more than one program at a time to be active Allows printing while still doing word processing I/O is slow and operating system wants to keep CPU busy Formats disks OS is a traffic cop =================== Partitioning - Dividing into separate parts. For example the hard drive can act as if it were 2 hard drives. To the user and to the programs, only the hard drive may look as if it goes from address: 00,000,000 – 50,000,000 And to another program it may look as if the hard drive goes from 50,000,001 – 99,999,999 memory can also be partitioned and in each partition, a separate program can be running ___________________ | | | | | | | | w| e | super | | o | x | mario | Need to keep CPU busy | r | c | | | | d | e | | | | | l | | |

User Interface User interface: The part of the operating system that the user sees and communicates with. Two ways GUI (Graphical User Interface) - Icons (graphical representation of command choices) are selected using an input device, usually a mouse. Command line - Commands are typed in using the keyboard. Example: >copy c:paper.txt a:*.* GUI Commands to start a process is given by clicking the mouse’s button Drag and Drop: dragging one icon over the top of another and releasing – used to copy files or move them Command-line interface VS. GUI interface. Command-line is one in which communications are given to the computer by typing commands on the keyboard. Used in MS-DOS -- not user friendly and prone to mistakes

Files and File Management File: the name given to any program or chunk of data that is stored on floppy, hard disk. CD ROM, or other storage. Extensions: A 3-letter extension is added to the file name separated by a period. Helps the operating system identify the type of file. OS then knows what program to load to open the file when you double click on the file Example: index.htm identifies a document called index that is made up of HTML code. Extensions – the ending of the file’s name after a period. It identifies what type of data and what program created it doc – MS Word xls – MS Excel jpg, jpeg – Joint Photographers Expert Group gif – Graphics Interchange Format wav – audio standard for Windows mov – quick time movie.

Files and File Management File System: Hierarchical File system organizes files in a treelike structure or hierarchy. Organizes files into groupings folders Hierarchical File Structure is a tree like structure Flat file structure – filing system that organizes files in one list (alpha, date) like a phone book Hierarchical – organizes file in a tree like structure. To find a file start at the root and go group by group until found. Folder – grouping of files under a single name - group like items together

Input & Output of Information - Device Control Installing a new device: A physical connection must be made to the peripheral. The proper software drivers must be added to the operating system Device Driver: A program that will allow communication between the operating system and another part of the computer, usually a peripheral device like a printer or scanner. It is an addition to the operating system.

Memory Concerns: Cache and Virtual Memory If the primary memory were as large as ever needed and as fast, the following ideas would not be necessary. Cache memory: Used when the speed of memory access is too slow - can’t keep up with the CPU’s needs. Very fast memory used by the operating system to house the data and instructions that are currently being used. 1.Cache – used as a staging area. 2. OS anticipates the next instructions and loads it into cache 3. Cache memory is very fast and very expensive that is why all of memory is not cache. 4. The interaction is between ordinary RAM and a special type of very fast and expensive RAM.

Memory Concerns: Cache and Virtual Memory Virtual Memory - addresses the problem of a program being too big to fit into the available RAM. The operating system divides the program into pieces. The pieces are stored on the hard disk as if it were additional RAM memory needed by the program. The pieces are retrieved into RAM as needed. Disadvantage: This slows the system down, because retrieval of information from the disk is time consuming.

Multitasking Allows several application programs to be in RAM memory at one time. Allows the operating system to control more than one program simultaneously. Each program “stealing” CPU time. Example: Playing a game while a large document is being printed. In a multiprocessor system the OS also allocates jobs to keep each of the CPU’s busy (von Neumann) Bottleneck: Microcomputers having only one program counter can run only one program at a time. The CPU can only process a single instruction at any one time, no matter how many tasks there are.

Summary An Operating System is a collection of programs Basic tasks of OS BIOS and booting of OS GUI and command line interfaces Cache and Virtual Memory