Since the computer doesn't understand any language more advanced than binary, using them could be a very tedious, error prone, and time consuming process. For this reason, operating systems have been developed. An operating system is a collection of commands that allow you to interact very directly with your computer's system components such as the hard drive and RAM. Some of the more common operating systems for PCs are DOS, Windows, Unix, and OS/2. In the case of Macintoshes however, there is only 1 standard operating system. This is an operating system called System 7.5 (where 7.5 is the version number).
DOS (Disk Operating System) historically has been (or was until the release of Windows 95) the most common and widely used operating system for PCs. However, this does not mean that it is the best or most powerful language. It just means that for some reason, software developers decided to write more programs for DOS than any other language. So if a user wants to have the highest number of programs available to them, they have to get DOS as their operating system. So more programs are written for DOS and the loop just keeps continuing until DOS is the standard PC operating system.
DOS has many applications and utilities which can be used to view, change, create, or optimize things on your computer's hard drive. DOS stores data on the hard drive with two main structures. The first structure is the file. Files are anything on the hard drive which can be recognized by DOS as containing data and that isn't a lost cluster on the disk. The other type of structure is the directory. Directories contain no data, but they are very useful in helping to organize the files on the drive. Without directories, all of the files on the drive would be cluttered together and nearly impossible to sort through.
Since the hard drive is divided up into directories and files, it is necessary to have commands available to the user to allow them to maneuver and navigate their way around the drive. These commands are dir and cd. Dir is short for directory. Typing it in results in a list of all files and sub-directories in the current directory appearing on the screen. Also, next to each file, the size in bytes, date, and time of the file is shown. In addition to this individual file information, the free space available on the current drive is shown at the end of the list. The other command, cd, stands for change directory. So by typing cd and a directory name, the current directory changes to the directory name that was typed after the cd command. An additional note: every directory has at least two other directories in it--even if it has nothing else. One is called "." and the other is called "..". "." is the current directory and ".." is the parent directory. So by typing "cd .", you remain in the current directory (effectively accomplishing absolutely nothing). And by typing "cd ..", you leave the current directory, and go to the directory which contains the directory that you were just in. Also, by typing "cd \", you change the current directory to the root directory for the current drive. One last navigation command in DOS is the command that allows you to switch drive letters. Normally, floppy drives are the "A drive" and "B drive" (this one is optional). The hard drive is always the "C drive". After that could be any other auxiliary storage device such as other hard drives, CD-ROMS, optical drives, etc. Finally, all of the network connections have the remaining drive letters.
DOS has a certain way of naming files and directories. Any name for either
type of structure can only have 8 characters before the period (.) and 3 after
it. The 8 characters before the period are considered to be the file or
directory name, and the 3 after it are considered to be the extension. An
extension is normally used to give information as to the type of file it is.
For example, files with the extension ".exe" or ".com" are
executable programs. Files with the extension ".bat"
are batch files. They are like programs in a way, but are more simple. Batch
files are a list of system commands for the system to carry out. Here is an
example batch file:
This batch file will switch drives to the c drive (or stay there if it is already there), change directories to the root directory, change directories to the games directory, run the program with the file name of chess, return to the root directory, and clear the screen. By using this batch file, the user only must type in the name of the file and the computer will run chess. Without the batch file, the user would have to type all of those commands in the batch file every time they wanted to run the chess program. This makes batch files very useful--especially if you are doing a lot of the same sequences of system commands over and over again.
DOS also contains commands to fulfill the other part of necessary items for an operating system--tools for optimizing the hard drive. The first of these commands is "chkdsk". Chkdsk makes a routine run through on the drive to check for lost file clusters. A more powerful version of chkdsk, called "scandisk", gives you the options of freeing up the space in these lost clusters or converting them to files. Scandisk can also perform a surface scan on the drive. This checks it for physical problems where the drive may have been damaged. The next optimization tool that DOS contains is "defrag". Defrag is a disk defragmenter. This is an essential tool because as files get changed and created and deleted, there isn't always a sequential block of free space on the hard drive. There may be enough free space total, but it's a little bit here and a little bit there. So the file will get stored in different places all over the drive. To keep track of where the pieces of the file are, entries are added/modified in the file allocation table, which is part of the drive. But if this table gets too complicated, it can become corrupt or be lost. Then the computer as well as the user would have no idea where all of the parts of the files were. That is why defrag is a very useful tool. It sorts out all of the files and realigns them in sequential order. This completely eliminates the file allocation table (until something gets changed again) so there is no risk of losing it. Not only that, but the computer will be faster since it doesn't have to keep looking everywhere for bits and pieces of files--it can just read straight through them.
Windows is the graphic environment of DOS. It is DOS based, but is a more user-friendly environment. It can sometimes be scary to sit down to a command prompt if you don't know any commands. But in Windows, it is much easier to figure out how to do things. But you can still run a command prompt. This just means executing the file "command.com" which brings you to a prompt with Windows still running in the background. All you have to do to get back into Windows from the prompt is type "exit".
One way Windows makes things easier to understand than DOS is that it has graphic representations of the abstract concepts of "file" and "directory". Windows uses icons to explain what type of file or directory a structure is. Folders represent directories, pieces of paper represent text files or files of unknown format, gears represent configuration files, and most applications and graphics files have built-in icons. To make navigation easy, there is another type of structure while in Windows. It is really a type of file, but it serves a purpose similar to another type of structure. This is the "shortcut". A shortcut is a program with a little arrow in the corner. Shortcuts allow you to have icons for applications anywhere on the computer without having to copy the file everywhere. This saves a lot of hard drive space since you only have to copy a 700 byte file into more than one place instead of an application which could easily be over 10 megabytes.
Since Windows is a much more intense operating system than DOS, it requires more RAM. In fact, it sometimes requires more than the computer has to offer. But this doesn't mean that the computer just stops, or freezes up (although it does happen sometimes). Instead, Windows creates a virtual memory file. This means that it creates a file on the hard drive that it uses as RAM once the normal RAM on the computer has all been used up. As you can imagine, when the computer is using virtual memory instead of normal memory, it is much slower. But by using this method, Windows can exceed the limits of the amount of RAM on the computer.
Unix is one of the most powerful and most useful operating systems in existence for PCs. It can be used for a single person using one computer, or it can be used on a minicomputer with many users at once. In appearance, it operates much the same as DOS. However, it actually does things much more efficiently. Instead of a command tying up the computer until it's done, as in DOS, Unix will perform all commands in the background. So you can have many tasks running while you work. The results just get returned when the task is finished.
Navigation in Unix is a lot like DOS as well. To view all of the files and directories in the current directory however, the command "ls" is used instead of "dir". To move between directories, the cd command is still used. But look out--unlike most other operating systems, Unix is case sensitive. This means that "cd" will work, but "CD", "Cd", and "cD" won't work as they did in DOS. This is also true for file and directory names. They must all be typed exactly the way they are on the hard drive.
Because of its extreme similarity to programming in C, CIRCUIT will redirect you there if you would like to learn about batch programming in Unix. Click here to go to programming in C.
OS/2 is a very powerful language that integrates the underlying System Object Model (SOM) with a complete object tracking system. This means that unlike in Windows, when you move an application, any links or references you have created (such as icons or associations) are automatically changed to reflect the updated system. Also, SOM allows the WorkPlace Shell interface to be fully manipulated by applications. An example of this the cc:Mail for OS/2. It uses SOM to integrate its in/outbox interfaces seamlessly with the WorkPlace Shell desktop. This level of integration isn't possible in most other operating systems because since their shells are not themselves an object.
OS/2 lets you run Windows applications in their own separate sessions called VDMs (Virtual DOS Machines. This is unlike Windows, because windows has a Single System VM (Virtual Machine). So if an application fails under OS/2, the effect of the failure is contained within the individual session. Other applications and the operating system remain unaffected. OS/2 also retains much of the Windows 3.1 code base, so it is highly backward compatible with Windows 3.1 applications and device drivers.
OS/2 features true preemptive multitasking of native applications. OS/2 can continue to multitask dozens of concurrent programs, and it can service multiple concurrent requests. This operating system's ability to run programs in separate VDM's allows it to preemptively multitask 16 bit Windows applications which Windows 95 cannot. So, you can have DOS, Windrows, and OS/2 applications running concurrently.
Click here to see a chart comparing the two graphic environments of OS/2 and Windows 95
Since CIRCUIT has said almost nothing about Macintoshes, this section will talk about not only their operating system, but the computers themselves, as well. When the first Macintoshes came out in 1984, they were a major step forward in computing. They were one of the first examples of a graphic operating system--using folders to represent directories, etc. as mentioned before with Windows. Later, in 1994, they switched their architecture to that of the PowerPC and began begin called PowerMacs. In 1995, they changed bus types to PCI. As far as the operating system goes, System 7 came out in 1991 followed by System 7.5 in about 1994. The current version is 7.5.3, but the third number doesn't mean any functionality change from 7.5. System 8 is scheduled to come out in early 1997.
Something unique about Macs is their cohesion of operating system and hardware. This means that Plug-and-Play is actually a reality on Macs while on other systems, there are some software packages that come close, but still require some help from the user in identifying new hardware. Also, System 7.5 is a cooperative multi-tasking, non-protected-memory system (another similarity to Windows). This means that applications can be running in the background while the user does their work in the foreground. System 8 is supposedly a good deal better than System 7.5 and should turn Macs into true preemptive multi-tasking/protected-memory systems. This means that the processes and applications running in the background can't trash the operating system's memory or monopolize the processor and make everything run extremely slowly for the foreground applications that the user is currently using.
CIRCUIT is sorry that this is all it has on Macs. But this page will evolve by the messages added to our message boards, and Macs are one of our topics. Here are some other links that may be useful for information about both Macs and their operating systems.