Homework 4 Solution Notes

Below please find a collection of notes and comments culled from student solutions. The "correct" answer --- by definition -- is something that only can be provided by the court system. Stay tuned...

1. What are the key technical questions regarding incorporation of a WWW browser into windows? Why are these questions interesting or relevant to this anti-trust litigation?

First, here is a list of key technical questions regarding the incorporation of IE into the windows operating system.

1). Exactly what is the definition of an OS? Having such a definition is relevant, since from the definition we could determine if a browser should be considered an integral part of the OS. To examine the definition of an OS, we must answer some questions:

• What are the functions of an operating system? What are the necessary components of an operating system? And, in particular, can a browser be a component of an OS?

• Is the shell a part of an operating system? This issue is subtle, because a shell is often regarded as an application by an operating system but most operating systems provide a default shell to facilitate interaction with users. IE can be used to view local files and launch local applications, so IE performs tasks usually handled by a shell. If a shell is defined to be part of an operating system, then Microsoft may argue that IE is an integral part of the Windows operating system. However, another question must then be addressed: Is it reasonable for a shell to support browsing?

2). How is IE integrated into the OS? We must rule out the possibility that IE still exists as a separate application.

According to Microsoft, IE 4 contains nine components that interoperate. These components include five DLLs---Wininet.dll, Urlmon.dll, Mshtml.dll, Shdocvw.dll, and Comctl32.dll---along with two executable files---Explorer.exe and Iexplore.exe---and a security and a Java virtual machine component.

• Shdocvw.dll (Shell Document View) lets developers build browser capabilities into software.
• Mshtml.dll is the component that contains routines to generate dynamic HTML. This is used, for example, to browse folders as html pages.
• Urlmon.dll lets developers treat URLs as if they were programmable objects and thus build them into applications (Microsoft's own Office 97 does this).
• Wininet.dll offers Internet services and capabilities, including HTTP and FTP access, modem dialing, and browser caching.
• Comctl32.dll (Common Controls) provides low-level support for menus, toolbars, progress bars, and many other controls used across Windows applications.
• The Java VM allows Java applications and applets to execute.
• The security module adds support for the SSL (secure sockets layer) standard.
• OLE/DCOM is Microsoft's Component Object Module, which is vital for windows applications to exchange data and work together.
• Iexplorer.exe and explorer.exe are wrappers for functionality that has been embedded into the operating system. Explorer.exe uses shdocvw.dll to supply a web interface where you URLs, local drives, or local network machine names are entered. Iexplorer.exe is basically a file that starts the explorer.

3). How does an OS support networking? There is no doubt that managing networking hardware is the job of an OS. But which layer of networking protocol should an OS offer to applications? Usually, an OS will offer primitives of the TCP layer (e.g., winsocket). If an OS can arguably offer services of the network application layer, then a browser arguably can be included in OS; otherwise, the browser should be considered an application.

4). Is the web an extension of file system? File management is a traditional function of an operating system. If the web is considered as being an extension of the file system, an OS should support browsing. Since the web is a collection of html files distributed on the computers connected by Internet, it is sensible to regard the web as being a network file system. But the issue is a bit more complex. One might argue that interpreting the contents of files (e.g., displaying html files, which IE does) is not a function of file system.

An operating system is a program that acts as an intermediary between applications and computer hardware. It has three main functions:

• Present users with a virtual machine that is easier to program than the underlying hardware. To programmers, such a virtual machine appears as a group of system functions, known as the application programming interface (API).
• Manage hardware resources. An operating system should implement an orderly and controlled allocation of the processors, memories, and I/O devices among competing programs. In order to manage the long-term storage, like disks and CD-ROM, an OS usually offers an abstract file system for applications.
• Security and protection. Since most large computer systems are shared by a number of users, each user must be protected against other users.

This definition of an operating system is based on taking a layered view of a computer system. A computer system can be regarded in terms of 3 layers: hardware, operating system, and applications. Users only see the application layer. Note that:

1. The shell thus would not be considered a part of operating system.
A shell is merely the first application that an OS loads into memory. Users can change the shell with which they interact, if they want (so the shell is not an essential part of the OS). The exection of applications doesn't rely on the shell.

2. The functions of a file system include:

• Creation and deletion of files.
• Access to files for reading or writing. The basic problem in accessing a file is to map a symbolic file name to a physical location.
• Protecting files against system failure.
• Allowing users to share files.

3. An OS should manage the networking hardware and offer communication methods (protocols), such as TCP, HTTP, or FTP. Applications use these protocols to send and receive information through networks. The operating system need not know the contents of the information being transmitted through the networks. So one can argue that browsing (displaying html files) is not the job of operating system.

4. Common components of applications are not parts of operating system.
And, even though different applications may implement common functions, this does not make those functions part of the operating system. For example, browsing may be a function implemented by many applications. An OS should make the use of resources efficiently, so it may well provide some mechanism to support code sharing. Windows offers the dynamic-link library (DLL) for sharing code by different applications. Some parts of operating system may even be a DLL. But this does not imply that a DLL is necessarily part of the operating system. IE can similarly offer a common function (browsing), but that doesn't mean that IE is a part of Windows.

An OS is a program that acts as an intermediary between a user of computer and the computer hardware. The OS is responsible for providing an environment in which a user can execute programs. The primary goal of an operating system is thus to make the computer system convenient to use. A second goal of an OS is to facilitate using computer hardware in an efficient manner. Thus, an operating system fulfills four main functions:

• Provides the base upon which the application program can be written.
• Manages resources on the computer system, including hardware and information resource (files).
• Security and protection.
• Provides users with a means of manipulating programs and data within the computer system. The user is presented with an interface that allows specification of a computation. The interface must be easy to use.

1. The shell is a part of operating system.
This point follows from the common feature of all current operating system: they all provide a default shell. But there are more convincing reasons for arguing that the shell is part of an operating system.

• The basic function of an OS is to make a computer usable. Without a shell, users will have a more difficult time using the computer.
• Second, a shell program controls the execution of other applications. For example, a user can kill a process by using commands implemented by a shell.

2. The shell should support browsing.
Why does a shell need to browse www directly instead of merely supporting the use of a browser for that function? The answer is that the shell of a modern OS should have a friendly and consistent user interface. The designers of Windows find that they can offer a more friendly and consistent user interface by integrating the browser into Windows Explorer (the former shell of Windows). The Internet then becomes an important resource for applications, so it's desirable for the browser to have the ability to launch remote application directly, which is the main function of shell program. Thus integrating the browser and shell is natural.

3. WWW is a kind of network file system.
WWW is a collection of html files distributed on the computers connected with Internet. It is a kind of network file system. The structure information of this file system lies in the links among html files, so an operating system should understand the format of html files and implement browsing. In contrast to the case for a local file system, the operating system must understand the format of directory files. Moreover, using FTP, a browser can access remote files (not only html files).

4. An operating system should provide support for a graphical user interface (GUI).
Having a GUI turns out to be important for many users. But why should an OS offer support for GUI in its API, as Windows does? There are two reasons:

• By our definition of OS, the primary goal of an operating system is to make the computer system convenient to use. Users like uniform user interfaces. By offering components of a GUI in the API, applications can employ a standard GUI.
• An OS may put a part of or all of GUI subsystem into it's kernel to speed up the display of information using that GUI. For example, Windows NT 3.1 implements a user-model window display subsystem, but for efficiency, Windows NT 4.0 implements the window display subsystem in it's kernel.