Project 2
I have moved back the due date for the WWW Searching Project to Monday, October 28th.
Part I of the assignment is to write a 3-5 page paper (double spaced) on the topic you select using material you found on the WWW.
Feel free to narrow your topic enough so you can write a decent paper on it.
Part II of the assignment is to write a 1-3 page narrative of your search - briefly describe what resources you used and how your search proceeded. What exciting things did you find?
You will be graded primarily on the depth of your search, as reflected by your narrative and the material in your paper.
I am more interested that you learn how to use the WWW effectively to search than that you write a technically great paper. Experiment with multiple search engines, and explore newsgroups.
Operating Systems
Operating systems are programs which control access to the hardware resources of a computer system.
We have seen that the computer hardware deals with memory addresses and the CPU, things we as people do not want to have to worry about. The operating system manages all these low-level details for us, so we work on the level of "run this program" or "get the file named ..."
Multiprogramming
One amazing things operating systems can do is share the CPU between more than one program. This is called multiprogramming or time sharing.
The operating system can keep more than one program in memory simultaneously, and every 1/100th of a second switch access to the CPU between them. To restart the job, all we must do is remember where in the program we were, and any values in the registers.
The amazing thing is that most of the time people need never realize that they are sharing the computer, since the switches take place so fast, and most of the time people/programs are idle anyway!
Other Functions
Main memory management by the OS includes keeping track of which memory locations are free or in use.
The disk file systems - the names and directories, are maintained by the operating system.
Virtual memory is a way to fool the CPU into thinking it has more main memory than it does, by swapping things with the disk
To print a file while using the computer for other things, we need set up a job which gives characters to the printer at regular intervals. Such print spooling is managed by the operating system.
System Startup / Shutdown
When you turn on a computer, it starts running a program in ROM to set things up, before turning over control to the operating system for more set up. This process is called booting the computer.
The boot process takes a few seconds to a few minutes, and typically checks memory and other hardware devices.
The boot process can be customized by the user to do extra things on startup, like check for mail.
Since the goal of an operating system is to be somewhat portable across machines, the lowest level details of how to read/write memory/disks is typically on the ROM, in a program called the BIOS (Basic I/O System)
Because certain data on file changes kept in memory while running the operating system, these must be written to disk before powering off the computer. To prevent your files from being messed up, you must exit or shutdown Windows before hitting the power switch.
System Security
The operating system is responsible for system security - making sure that only authorized users are allowed access to certain files.
Security is particularly important in multiuser or network machines.
Security is important (1) to stop bad people from doing bad things, (2) to stop good people from doing dumb things (like deleting all files)
Typically, security is implemented using accounts and passwords.
Selecting good passwords is hard to do, but important! They must be long enough that a computer cannot try all of them by brute force.
They must be random-enough that a computer cannot try all names and dictionary-words to find it, yet it must be easy enough to remember that you don't write it down where someone else can see them.
Interfaces to the Operating System
The resources controlled by the operating system can be accessed in three typical ways.
The graphical user-interface (GUI) gives you access to the resources by pointing and clicking
The shell or command-language gives you access to the system via a language commands you type in the keyboard. MS-DOS is the command-language for Microsoft Windows. The command language is typically clunkier to use than GUI, but more powerful for certain things.
System calls are a set of program parts (subroutines), so programmers can write programs which use things controlled by the operating system, like reading/writing from disks, or printing. Differences in the system calls are another reason why Macintosh programs cannot run on Windows, etc.
The Power of Microsoft
Microsoft Windows is the standard operating system for almost all PCs. Having a standard operating system is good - since all applications programs can assume the same standard environment.
However, this gives Microsoft enormous advantages in selling other computer products and services, which can be unfair to other companies.
Since all applications software needs to work with the operating system, Microsoft can work their application software before their competitors know about the changes.
Since they can include extra software with the operating system, they can eliminate the need to buy products other companies make, such as modem programs, disk compression utilities, and WWW browsers.
Since they control access to things, they can make it easier to use Microsoft products than other companies, i.e. the Microsoft Network.
Because of this power, there has been calls that Microsoft should be broken up as a monopoly.