Windows NT, Terminal Server and Citrix MetaFrame Terminal Server Architecture

Transcription

1 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 1 of 13 [Figures are not incuded in this sampe chapter] Windows NT, Termina Server and Citrix MetaFrame Termina Server Architecture IT IS TIME TO BEGIN your exporation of the core architecture of the Termina Server operating system. Because Termina Server is based on Windows NT Server 4.0 you wi find that, for the most part, their architecture is very simiar. For those who are aready famiiar with the intricacies of Windows NT Server 4.0, the chapter begins with a discussion of the main differences between Windows NT Server 4.0 and Termina Server. You wi earn how, in the Termina Server Edition, key components of NT Server 4.0 have been rewritten to support a mutiuser environment. For those who want more, this discussion is foowed by a much more detaied coverage of Termina Server architecture. This information is fundamenta to your understanding and administration of the Termina Server product. Architectura Differences Between Termina Server and NT Server 4.0 Before you get into the detais of both NT Server 4.0 and Termina Server 4.0 architecture, spend a moment earning the differences between the two. The fundamenta difference is that Termina Server architecture supports mutipe sessions or desktops running at the same time, whereas NT Server 4.0 supports ony one--the consoe. Each session running on Termina Server must be isoated from the actions of a other sessions. Termina Server handes this need by assigning each new session a unique Session ID. The Session ID is used to keep track of and keep separate each session s resources. Athough many components of the NT Server 4.0 architecture have been modified in Termina Server, the three most significant components that have changed are the Object Manager, Win 32 subsystem, and the Virtua Memory Manager. Differences in the Object Manager The Object Manager is responsibe for creating, managing, and deeting operating system and appication objects. In the mutiuser environment of Termina Server each session must keep its objects separate from those of the other sessions. To keep them separate, Termina Server appends the Session ID onto the end of each object that is created within the session. Using the query object Termina Server command, you can actuay see this process in action. The query object command shows you a ist of a current objects on the system. The ist is usuay rather ong so you may need to dump it to a text fie (query object > objects.txt). fie://i:\chapters\z\zc844.htm 3/21/01

2 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 2 of 13 The foowing output shows two of the many objects in the object ist. Note the :1 and :0 that have been appended to the object names. These are the Session IDs of the sessions that these objects beong to. Had Termina Server not kept these identica object names unique, using the Session ID number, they coud not have been created. C:> query object... \BaseNamedObjects\NDDEAgent:1 \BaseNamedObjects\NDDEAgent:0... Semaphore Semaphore Differences in the Win 32 Subsystem The Win 32 subsystem mainy handes graphica dispay requests and other Win 32 API cas for appications running on Termina Server. On NT Server 4.0, a singe instance of this subsystem is created, when the server is first booted, by the Session Manager (smss.exe). This instance handes the graphica dispay of the NT Server consoe desktop. Because Termina Server must keep track of mutipe desktops simutaneousy, each session created on it must be assigned its own Win 32 subsystem. As with the Object Manager, Termina Server distinguishes the processes running in the different Win 32 subsystems using the Session ID. In this way, Termina Server is abe to keep a of the desktops running on it separate. Rea-Word Tip: Gaining a Deeper Understanding with NT Utiities Many of the concepts of Termina Server architecture can be difficut to grasp and remember uness you can actuay see them in action. Fortunatey, there are severa utiities, such as the query utiity incuded with Termina Server, that hep you see what is actuay going on inside. Not ony are these invauabe earning toos, but they doube as great troubeshooting toos. From time to time I wi highight where you can use a particuar too to gain a deeper understanding of the topic at hand. Creating the Separate Win 32 Subsystems Much ike NT Server 4.0, when Termina Server first boots, the Session Manager (smss.exe) starts a Win 32 subsystem for the consoe. Under Termina Server, the consoe is aways assigned Session ID 0. After the consoe processes are started, the Termina Server service (termsrv.exe) instructs the Session Manager to start up two ide instances of the Win 32 subsystem to wait for cient connections. By going into the Task Manager on your Termina Server (Ctr+At+De, Task Manager) and seecting the Processes tab, you can actuay view the instances of the Win 32 subsystem that have been oaded (see Figure 3.1). The key user mode process in the Win32 subsystem is the Cient Server Run-Time Subsystem process (csrss.exe). The CSRSS handes some of the non-graphica Win 32 API functions. Every instance of CSRSS aso starts an instance of the WINLOGON process (winogon.exe), which is responsibe for the initia handing of the cient ogon. Note in Figure 3.1 that there are mutipe instances of the CSRSS and WINLOGON processes and that each is assigned its own Session ID (ID coumn). fie://i:\chapters\z\zc844.htm 3/21/01

3 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 3 of 13 Differences in the Windows Manager and Graphics Device Interface The Windows Manager and Graphics Device Interface (GDI) are the kerne mode portions of the Win 32 subsystem responsibe for windows management and the handing of Win 32 API graphics cas. They both run as part of the win32k.sys system fie. Because they are both part of the Win 32 subsystem, there is a separate instance of them running for every session. The main difference between NT Server 4.0 and Termina Server is with the GDI. Under NT Server 4.0, the GDI interacts directy with the video dispay driver for the server consoe. Suppose you are running Microsoft Paint at the server consoe. When you draw something in Paint, the Paint program makes a Win 32 API ca to dispay what you are drawing onto the screen. This API ca is eventuay passed to the GDI. The GDI then instructs the video driver what to dispay by using standard video driver interface commands. FIGURE 3.1 Processes in Task Manager. Athough this technique works fine for server consoe dispay on Termina Server, it does not work for remote termina sessions. On Termina Server, the GDI dispay commands must be packaged and sent across the network for dispay on the remote terminas. Termina Server and MetaFrame both hande this through virtua dispay drivers. Both the RDP and ICA protocos have their own virtua dispay driver. Each remote session on Termina Server runs its own instance of one of these drivers. The driver captures the video driver interface commands from the GDI. These commands are packaged up by the protoco and sent across the wire for dispay on the remote cient. Differences in the Virtua Memory Manager The fina major difference between NT Server 4.0 and Termina Server 4.0 is in the Virtua Memory Manager. The Virtua Memory Manager maps virtua addresses used by processes into actua physica ocations in the computer s memory. Each process running on Termina Server is given up to a 2GB virtua address space within which to work. Because each process s space is kept track of separatey, this NT Server 4.0 architectura convention works we with Termina Server. The difference occurs within the 2GB virtua address space used by the operating system itsef. Because a processes running on server need access to certain areas of this operating system memory, the processes woud confict in a mutiuser environment. The main cuprit is actuay the kerne mode component (win32k.sys) of the Win 32 subsystem. NT Server 4.0 was designed to run ony one instance of this subsystem, which it oaded into the operating system memory space so that processes running on the consoe coud have access to it. Because the arrangement of much of the operating system memory space was fixed, Termina Server had to use a specia technique to run mutipe instances of the Win 32 subsystem. To sove this probem, Termina Server assigns each session its own virtua Session Space. Any memory cas to the Win 32 subsystem memory range by a particuar session are redirected to that session s Session Space by Termina Server. This redirection keeps each session s Win 32 subsystem memory separate from that of the other sessions. Note for WinFrame Administrators: User and Kerne Mode For those famiiar with the architecture of NT Server 3.51 and WinFrame 1.x, it may fie://i:\chapters\z\zc844.htm 3/21/01

4 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 4 of 13 seem strange to tak about user and kerne mode components of the Win 32 subsystem. Under NT 3.51 and WinFrame the Win 32 subsystem ran entirey in user mode. One of the main architectura differences between NT 3.51 and NT 4.0, and thus between WinFrame 1.x and Termina Server, is that significant portions of the Win 32 subsystem have been moved to kerne mode to improve efficiency. Windows NT Design Goas For those who want to know more about Termina Server architecture, you wi note that this section starts at the beginning, with the deveopment of the operating system it is based on. The design goas of the NT operating system are a arge part of the reason why NT was originay chosen by Citrix for its mutiuser product WinFrame, and why Termina Server, which evoved from WinFrame, is possibe. When the deveopment team for Windows NT was first formed in 1989, its mission was to design an operating system to meet the foowing design goas: Extensibiity For an operating system to be extensibe, it must be moduar with we-defined interfaces for appications to pug into. The extensibe nature of NT is what makes Termina Server possibe. Robustness An operating system must protect itsef and other running appications from appications that "misbehave." This is especiay important in the mutiuser environment of Termina Server, in which severa users can be running severa appications at once on the same system. Scaabiity For an operating system to be used by major corporations, it must be scaabe. You shoud be abe scae from serving a handfu of users to severa hundred users on one server, by simpy adding more hardware (processors and memory). Portabiity The operating system must work with mutipe hardware architectures and be abe to be easiy ported to new ones. Compatibiity NT must work with appications from severa different operating systems, incuding OS/2, POSIX, DOS, and Windows 16-bit. Performance Athough feature-aden, the operating system sti must maintain a competitive eve of performance. These design goas were met by using a highy moduar architecture. The next section shows how Termina Server takes advantage of this moduarity to work within a mutiuser environment. Components of the Termina Server Architecture The goa of this section is to provide a thorough understanding of the underying structure of Termina Server. You wi find that a thorough understanding of the operating system's operation at this eve wi hep you to better troubeshoot Termina Server and optimize its performance. fie://i:\chapters\z\zc844.htm 3/21/01

5 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 5 of 13 This section starts with the Termina Server architecture diagram shown in Figure 3.2, and as you proceed through this section, the function of each part of the diagram is expained. As each part is described, refer back to the architecture diagram to see how a specific part fits in with the whoe architecture. FIGURE 3.2 Termina Server architecture. Components of the Termina Server operating system run in one of two modes: user or kerne: Kerne mode In kerne mode, an appication has direct access to the hardware. Exampes of kerne mode appications are the HAL, Microkerne, Virtua Memory Manager, and device drivers. Because the appications are running in kerne mode, the system is not protected from them, and as a resut, they must be written and tested very carefuy. One poory written appication can ock up or crash the entire system. User mode In user mode, an appication can access hardware and operating system resources ony through the Win 32 subsystem. This ayer of isoation provides a great amount of protection and portabiity for appications. Exampes of appications running in the user mode are DOS appications, Windows 3.x (16-bit), Windows 32, POSIX, and OS/2. If a user mode appication crashes, the crash affects ony the process the appication is running in. By using Task Manager, you can simpy deete the frozen process. A other appications continue to run without interruption. The underying difference between kerne and user mode has to do with the processor priviege eve. Kerne mode is often referred to as privieged mode. On most modern processors, incuding Inte and Apha, you can run an appication at different priviege eves. On the Inte processors, there are four priviege eves or rings in which appications can run: 0-3. In reaity, kerne mode refers to programs that run at priviege eve 0. These programs have unrestricted access to a hardware and memory in the system. Programs running at priviege eve 0 can set the priviege eve for programs that they ca. In contrast, user mode refers to appications and subsystems that are set by the kerne to run in priviege eve 3. In this mode, appications are "boxed-in." The processor aows them to work ony within their own memory areas. The processor aso restricts them from directy accessing I/O, such as disk drives, communications ports, and video and network cards. To access these devices, appications must make a specia gated ca to a kerne mode program that handes the hardware. Kerne Mode Components A description of the components that make up Termina Server must start at the heart of the operating system and work outward. The foowing sections first describe the Microkerne and HAL in detai and their reation to each other. These are the core components of the operating system. Next the Executive Services, which run in kerne mode, are covered. Microkerne Notice in Figure 3.2 that many of the moduar components of the Termina Server operating system are buit around a Microkerne. The Microkerne is a sma and very efficient program that handes the core functions of the operating system. fie://i:\chapters\z\zc844.htm 3/21/01

6 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 6 of 13 The Microkerne s primary job is managing the operating system s workoad. As a manager, the Microkerne takes the tasks assigned to it by the appications and divides the work between the server s microprocessors. In a mutiprocessor system, the efficiency of the Microkerne is critica. Without an efficient Microkerne, some processors become overburdened whie others remain ide. The Microkerne actuay resides in either ntoskrn.exe or ntkrnmp.exe in the SYSTEM32 directory. The ntkrnmp.exe fie is the mutiprocessing version of ntoskrn.exe. It is speciay written to hande mutiprocessor synchronization. Processes and Threads Termina Server appications and the operating system itsef divide their work between processes and threads. An understanding of the basics of how appications, processes, and threads interact is key to understanding how the Microkerne works. This knowedge is aso important when administering Termina Server. You need to know what processes and threads are when you use toos such as Performance Monitor, Task Manager, and the Termina Server Administrator. Processes A process is a program under contro of the NT operating system that in essence is given its own room in memory and resources to work with by the operating system. When a process is started, an address space is set up for it. A process has its own variabes and can request from the operating system its own access to the hardware beow it. The operating system keeps track of what each process is doing by assigning it a unique process ID. Furthermore, Termina Server keeps track of the processes that each session is running by assigning them Session IDs. When an appication is run, it can request that the operating system start up as many processes as it needs to do its tasks. Most appications run with one or two processes. Threads For processes to get any work done, they divide their work into threads and have the operating system execute them. A thread is a piece of executabe code that can be run on a singe processor. The Microkerne works by dispatching these threads to the processors based on their priorities. HAL The Hardware Abstraction Layer (HAL) is what the Microkerne communicates through when it needs to send threads to the processors or I/O devices. The HAL shieds the Microkerne from the differences in the hardware beow it. Suppose you are using a Micro Channe Bus instead of a standard PC bus, or various types of mutiprocessor arrangements. For each of these machine specific setups, a HAL is written, normay by the manufacturer. The HAL transates the standard HAL requests that the Microkerne makes into code that the processors and I/O devices can understand. In this way, the HAL provides a uniform interface for the Microkerne to use the capabiities of different hardware patforms. The HAL is aso used by many device drivers to access the hardware. The HAL shieds these drivers from the differences in the structure of the hardware beow them by providing a uniform interface. Rea-Word Tip: Processes in Action fie://i:\chapters\z\zc844.htm 3/21/01

7 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 7 of 13 One of the many ways to see processes in action is to use the query process utiity: 1. Log on as administrator to Termina Server. 2. Go to the command ine and run query process *. You wi see a ist of a processes running on the system, to whom they beong, and what their process IDs and session IDs are. Run your favorite program and ook at the processes again using the query process command. Notice the new processes that are created when your program opens. You can aso see processes in action by using the Termina Server Administrator too (described in Chapter 12, "Administering the Desktop and Server") and Task Manager (as shown in the earier "Differences in the Win 32 Subsystem" section). You can aso measure many performance parameters of the operating system by process by using Performance Monitor (described in Chapter 13, "Measuring Performance"). Rea-Word Tip: Viewing Avaiabe HALs with UPTOMP The HAL is impemented in the ha.d. Notice on the Termina Server CD under the I386 directory that severa fies start with HAL (HAL*.*). When you first insta Termina Server, you have the option of picking your processor. At this point, the appropriate HAL is expanded, renamed ha.d, and put in your SYSTEM32 directory. If you have the NT Server 4.0 Resource Kit, avaiabe from Microsoft, run the Uni to Mutiprocessor utiity (uptomp.exe) from the Start menu, by seecting Resource Kit 4.0, Configuration. By using this utiity, you can view a description of the various HALs on your insta CD. Executive Services There are seven primary Executive Services. These are the basic kerne mode components that the appications running in user mode use through the Win 32 API: Object Manager Security Reference Monitor Process Manager Virtua Memory Manager Loca Procedure Ca Faciity I/O Manager Windows Manager and Graphica Device Interface Refer to Figure 3.2 for a genera idea of how these components reate. The Executive Services are a kerne mode components that provide the operating system services that are used by the appications running on Termina Server. The foowing sections describe each of the kerne mode components in detai. fie://i:\chapters\z\zc844.htm 3/21/01

8 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 8 of 13 Object Manager One of the most important components in the Executive Services suite is the Object Manager. Because Windows NT is an object-oriented operating system, most of its resources are treated as objects. The Object Manager is in charge of creating, tracking, protecting, and deeting system objects. The Object Manager is responsibe for objects used in both kerne mode and user mode. As described in the section "Differences in Object Manager," the Object Manager keeps track of both goba objects that are used by a sessions and session-specific objects that appications running in a particuar session create. To truy appreciate the importance of the Object Manager, you must understand what objects are. Neary every time an appication accesses a fie, dispays something on the screen, communicates with a device, or accesses most operating system resources, it does so through an object. Objects have three main components: properties, methods, and handes. Properties Used to provide information to appications and users about the object. Methods Used for controing objects. Handes Used by the operating system to identify which object an appication is referring to. The foowing are exampes of some of the objects under Windows NT: Port objects Memory objects Process objects Thread objects Fie and directory objects Suppose an appication needs to access a fie on the hard drive. The appication woud access the fie through a fie object, as shown in Figure 3.3, which has properties such as fie name, fie size, date of creation, current status, and attributes. These properties aow the appication to gather information about the object. To do something with the object, the appication must use a method. Exampes of fie methods are create fie, deete fie, open fie, read fie, and cose fie. To keep the fie object unique, the operating system assigns it a hande. The hande is used by any appications that reference the fie object. Security Reference Monitor For an operating system to be secure, not every appication or user can have access to a resources on the system. This is especiay important with Termina Server, in which severa users can access the same resources remotey. For exampe, if the operating system is not protected, a singe Termina Server user coud accidentay deete a critica system fie that everyone needs. The Security fie://i:\chapters\z\zc844.htm 3/21/01

9 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect.. Page 9 of 13 Reference Monitor provides both authentication and auditing services to protect your server from instances ike this. NT security works through access contro ists (ACLs) and security IDs (SIDs). SIDs Every user and group in the security database has a unique identifier caed a SID. An exampe of a typica SID is S This unique number is associated with the user or group unti it is deeted. Even if another user or group is created with the same name the newy created user or group is assigned a different SID. ACLs Every Windows NT object has an access contro ist (ACL). An ACL is made up of access contro entries (ACEs). The ACE contains the SID of a user or group, aong with their security rights to this object. When a user ogs on to Termina Server, an access token object is created for him that ists his SID, the SIDs of a the groups that he beongs to, and specia privieges such as the abiity to set system time. In Figure 3.4, you see the access token object for the fictitious user John.Smith. Note that the object contains a of the SIDs for a of the groups that John.Smith beongs to. This object acts ike a set of keys to unock the system resources. When John.Smith tries to access the Office 97 directory, the Security Reference Monitor retrieves the ACL for this directory, compares it to the SIDs in John.Smith's access token object, and grants him Read and Execute rights to that directory. FIGURE 3.3 Accessing a fie through the fie object. FIGURE 3.4 Access tokens and ACLs. Another exampe is an accounting database fie with an ACL that aows the Accounting group fu access, but restricts the Management group to read access. When someone in the Management group ogs on, she receives an access token object that incudes the SID for the Management group that they are in. When she tries to access the accounting database fie, the Security Reference Monitor checks the ACL for the fie and finds that the Management group has ony read access to the database. The user is then aowed to open the database with read-ony access. If the user tries to write to or deete the database, the Security Reference Monitor prevents this action. Another important function of the Security Reference Monitor is auditing. Suppose the accounting database in the preceding exampe is set up for strict auditing. When someone tries either successfuy or unsuccessfuy to access the fie, such as an attempt to deete it, the Security Reference Monitor records the attempt. Process Manager In the earier discussion about the Microkerne, processes are described as being part of appications and having threads. The Process Manager keeps track of a processes running on the system and their associated threads. The Process Manager aso handes the opening and cosing of processes and threads. Every process is assigned a security access token when it first starts. The Process Manager works fie://i:\chapters\z\zc844.htm 3/21/01

10 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect..Page 10 of 13 cosey with the Security Reference Monitor to ensure that the process goes through security checks before accessing protected objects. Virtua Memory Manager The appications that run on your Termina Server need memory to hod their data and code. The Virtua Memory Manager is responsibe for keeping track of this memory and assigning it to your programs. In oder operating systems such as MS-DOS, there was a set amount of memory avaiabe and ony one program was oaded into it at a time. Under Termina Server there can be severa users simutaneousy running mutipe appications at the same time on the same server. For these appications to work together propery, they are each given their own bock of virtua memory. Appications are aowed to access ony their own memory and are bocked from accessing others memory. In this way, each appication runs in its own protected space in the Termina Server s memory. Each process running on your Termina Server is aocated 4GB of virtua memory. The first 2GB bock is for user programs and the second 2GB is reserved for operating system storage. This is a ot of memory. Few machines wi have even cose to this amount avaiabe. The magic of the Virtua Memory Manager is that athough you may not actuay have this amount of memory, to your appications it appears as if this amount is avaiabe. If you have a program that runs out of room, the Virtua Memory Manager swaps other portions of memory to the hard disk to make room for the running appication. To your appication, the memory sti appears as one contiguous space. Athough the memory assigned to your program appears contiguous, the actua physica ocations in memory where the program is stored does not have to be. The Virtua Memory Manager divides the memory and hard drive space avaiabe into 4KB pages It handes assigning these 4KB pages to your programs to actua physica memory ocations, as shown in Figure 3.5. Because programs are starting and stopping a the time on your server, without the Virtua Memory Manager there woud be gaps of avaiabe memory eft unused after a program reeases it. The Virtua Memory Manager fis in these gaps when programs make new requests for more memory. The Virtua Memory Manager aso provides very important performance information to your system. On Termina Server, having the right amount of memory to hande a users and appications is critica. If there is not enough memory, the response time sows down tremendousy for a users because the Virtua Memory Manager must swap out memory to disk to make room. In Chapter 13, you earn how to use Performance Monitor to effectivey monitor how much memory you are using, and how much you need. FIGURE 3.5 The Virtua Memory Manager. Loca Procedure Ca Faciity The Loca Procedure Ca Faciity (LPC) handes the cient/server communication between appications and subsystems and between processes. It handes ony those cas that occur ocay. The actua request is sent to the Win 32 subsystem, which in turn sends the request to the appropriate Executive subsystem for dispay. This eve of compexity is hidden from the appication, which must ony ca the procedure and receive a response. fie://i:\chapters\z\zc844.htm 3/21/01

11 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect..Page 11 of 13 Termina Server makes extensive use of LPCs. The Termina Server service (termsrv.exe), which handes most of the background administration necessary on Termina Server, uses LPCs to communicate with other processes. For exampe, when new connections need to be made, the Termina Server service cas the Session Manager (SMSS) to create ide connections that wait for new users who need to og on. I/O Manager The I/O Manager handes a input and output to your system s devices, and as such it is probaby one of the busiest subsystems. I/O Manager handes data input and output from a of the foowing and more: Hard drives using NTFS or FAT CD-ROMs Foppy drives SCSI devices such as scanners, or removabe storage such as a JAZ drive Seria and parae ports Tape drives Mouse and keyboard Network cards The I/O Manager incudes a cache manager that handes caching a disk and network input/output. Caching can improve performance greaty during heavy disk access by caching or copying data that it reads from the disk drive into memory. The next time this data is accessed, it is taken from memory instead of the disk, which resuts in much quicker access. Caching is aso beneficia during writes. A process can write to the cache by using the azy write service. Rather than the process having to wait for the disk to finish processing before sending it more data to the disk, the process simpy writes additiona data to the cache. The next time the processors are not busy, the cache is written to disk; meanwhie, the process can carry on uninterrupted. Whether you are connecting your cients to the Termina Server via the network, seria ports, or modems, the I/O Manager is the main Termina Server subsystem that they wi interact through. Because of this, it is important that you keep up with new reeases of I/O drivers so that you aways have the most up-to-date and efficient versions. Windows Manager and Graphica Device Interface The Windows Manager and Graphica Device Interface (GDI) are responsibe for handing a Win 32 API video requests by appications. They are the kerne mode components of the Win 32 subsystem. These components are covered in detai in earier section "Differences in the Win 32 Subsystem." fie://i:\chapters\z\zc844.htm 3/21/01

12 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect..Page 12 of 13 How the Windows Manager and GDI reate to the Win 32 subsystem is diagrammed in Figure 3.2. Note that there is one instance of the Windows Manager and GDI (win32k.sys) for every session running on Termina Server. User Mode Components So far, the discussion has focused on kerne mode components. The appications the users are running are in user mode. For Termina Server to support as many types of appications as it does, it has subsystems that emuate the native environments that these appications woud run in. There are environment subsystems for DOS, Windows 16-bit, POSIX, and text-based OS/2 appications. A of these subsystems are designed to basicay convert the foreign appication s cas into cas that Termina Server s native environmenta subsystem, the Win 32 API, can understand. Win 32 Subsystem The Win 32 subsystem handes most Win 32 API cas. A user mode appications communicate with the Termina Server operating system through this API. Because Termina Server is a stricty controed operating system, a interaction between appications and hardware must occur through the Win 32 API. Appications that try to impropery bypass the operating system and access hardware directy are shut down or stopped by Termina Server. This eve of appication security brings a great amount of stabiity to the operating system. Even poory written appications do not have the abiity to ock up the entire operating system with an improper direct hardware ca, such as a direct disk write. This is very important for Termina Server because it typicay is running severa appications at once for severa users. The Win 32 API, supported by the Win 32 subsystem, is an object-oriented set of functions and procedures that aows the appication to contro a aspects of the operating system. Because the Win 32 API for NT is very simiar to the one for 95, in genera, Win 32 appications can run on either API without modification. One of the main advantages of an API is the ayer of isoation it provides to the operating system. As ong as the Win 32 API stays the same, the entire kerne can be rewritten, and Win 32 appications woud sti run. The Win 32 subsystem can be divided into two subsystems: the Executive and the Consoe. The Executive subsystem resides in the kerne mode; it is made up of the Windows Manager and GDI. The Executive handes the majority of the graphics reated Win 32 API cas. The Consoe runs in the user mode and provides text window support, hard-error handing, and shutdown. The system fie that makes up the Consoe is Cient Server Runtime Subsystem executabe (csrss.exe). DOS and Windows 16-bit Appications To run DOS appications, you need a converter to take the appication s device cas and convert them to Win 32 API cas that Termina Server can understand. The modue that does this is the NTVDM or NT Virtua DOS Machine. The NTVDM simuates a DOS environment for DOS appications. It provides simuation for the foowing: Standard DOS 21 Interrupt services ROM BIOS cas fie://i:\chapters\z\zc844.htm 3/21/01

13 Windows NT, Termina Server and Citrix MetaFrame - CH 3 - Termina Server Architect..Page 13 of 13 Device cas, such as to the keyboard or video When a DOS appication runs on Termina Server, it is assigned three threads. The first thread is the one in which the appication runs. The second thread provides a heartbeat to simuate timer interrupts for the MS-DOS appications. Many DOS appications rey on the timer interrupt to time various procedures and to contro the execution of programs. The third thread is for consoe I/O. Athough you can run DOS appications on terminas attached to Termina Server, there are disadvantages: You can expect a 10-25% decrease in performance of a typica DOS appication due to the Win 32 transation. This extra processing time for transation reduces the amount of processing time avaiabe for other users of the Termina Server. You cannot run as many users concurrenty if a users are running DOS appications. Users cannot run DOS appications fu screen uness they are using the DOS-based cient. Because Termina Server comes with ony Windows-based cients, you cannot run DOS appications fu screen uness you purchase the MetaFrame add-on and use the DOS-based cient. 16-bit Windows was originay designed to be basicay a graphica operating system that runs on top of DOS. Because it was designed to run on top of DOS, many Windows 16-bit appications rey on DOS system cas, such as interrupt 21. For 16-bit Windows appications to run under Termina Server, Termina Server runs them on top of the NTVDM. This provides the DOS environment that they need. Consequenty, you face the same decrease in performance with Win 16 appications as you do with DOS. Windows 16-bit appications must aso make Windows API cas, such as to manipuate graphic objects on the screen. To do this, Win 16 appications must use a converter to convert Win 16 API cas to Win 32 API. That conversion is performed by the Win 16 on Win 32 or WOW exec. Like the NTVDM, the WOW takes its effect on system performance. You sti must have more memory and processing speed to run 16-bit Windows appications than for a simiar Win 32 appications. Because of the significant performance hits, it is not recommended to run DOS or Win 16 appications with Termina Server, if you have the choice. fie://i:\chapters\z\zc844.htm 3/21/01