PATENT DOCUMENT

Publication Number: US-7865579-B2
Application Number: US-48410706-A
Country: US
Kind Code: B2

Title: Method and apparatus for administering the operating system of a net-booted environment

Abstract:
A method and apparatus are provided for supplying a reliable and maintainable operating system in a net-booted environment. According to one embodiment, a network computer (NC) system including an NC server and multiple NC clients is managed by an NC client causing the remainder of the NC clients that are subsequently booted to receive operating system software that is configured differently than that currently in effect by replacing one or more system volumes on the NC server containing the operating system software with one or more different system volumes.

Claims:
What is claimed is: 
     
       1. A method performed at a first network computer (NC) client, comprising:
 receiving one or more first working copies of one or more first volumes; 
 modifying the one or more first working copies to generate one or more second working copies, wherein the modifying includes 
 generating a write request to the one or more first volumes; and 
 redirecting the write request to the one or more second volumes on a NC server over a network, wherein information associated with the write request is 
 to be stored in one or more second volumes at the NC server, wherein the one or more second working copies that include the one or more first copies that have been modified at the first NC client are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       2. The method of  claim 1 , wherein the one or more first volumes contain an operating system. 
     
     
       3. The method of  claim 1 , wherein the one or more first volumes contain an application program. 
     
     
       4. The method of  claim 1 , wherein the one or more first working copies are received by rebooting. 
     
     
       5. The method of  claim 1 , further comprising:
 initiating a boot process out of a local memory; 
 sending a first request for a boot information to the NC server; 
 receiving the boot information from the NC server; 
 sending a second request for a boot image to the NC server based on the boot information; 
 receiving the boot image from the NC server; and 
 executing the boot image. 
 
     
     
       6. The method of  claim 1 , further comprising
 generating a write request; and 
 redirecting the write request to the one or more second volumes at the NC server. 
 
     
     
       7. The method of  claim 1 , further comprising:
 sending a read request to the NC server; 
 determining if the read request is associated with the one or more second working copies; 
 sending the read request to retrieve first data from the one or more second volumes if the read request is associated with the one or more second working copies; and 
 sending the read request to retrieve second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       8. A method performed at a network computer (NC) server, comprising:
 copying one or more first working copies from one or more first volumes to one or more second volumes; 
 enabling of modifying of the one or more first working copies on the NC server by rebooting a first NC client to generate one or more second working copies; 
 receiving the one or more second working copies generated by the first NC client; and 
 replacing the one or more first volumes having the one or more first working copies with the one or more second volumes having the one or more second working copies that include the one or more first working copies that have been modified at the first NC client that are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       9. The method of  claim 8 , wherein the one or more first volumes contain an operating system. 
     
     
       10. The method of  claim 8 , wherein the one or more first volumes contain an application program. 
     
     
       11. The method of  claim 8 , wherein the enabling of the modifying is performed by rebooting the first NC client. 
     
     
       12. The method of  claim 8 , further comprising:
 receiving a first request for a boot information from the first NC client; 
 sending the boot information to the first NC client; 
 receiving a second request for a boot image from the NC client; and 
 sending the boot image to the NC client. 
 
     
     
       13. The method of  claim 8 , further comprising:
 receiving a write request to modify the one or more first volumes from the NC client; and 
 storing the information associated with the write request in the one or more second volumes. 
 
     
     
       14. The method of  claim 8 , further comprising:
 receiving a read request; 
 determining if the read request is associated with the one or more second working copies; 
 retrieving first data from one or more second volumes if the read request is associated with the one or more second working copies; and 
 retrieving second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       15. The method of  claim 8 , further comprising
 determining if the one or more second working copies are to be deleted; and 
 marking the one or more second working copies for deletion during a subsequent reboot of the first NC client if the one or more second copies are be deleted. 
 
     
     
       16. A machine-readable storage medium storing data that, when accessed by a machine, cause the machine to perform operations, comprising:
 receiving one or more first working copies of one or more first volumes; 
 modifying the one or more first working copies to generate one or more second working copies, wherein the modifying includes 
 generating a write request; 
 redirecting the write request to a NC server over a network, wherein information associated with the write request is 
 to be stored in one or more second volumes at the NC server, wherein the one or more second working copies that include the one or more first copies that have been modified at the first NC client are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       17. The machine-readable medium of  claim 16 , wherein the one or more first volumes contain an operating system. 
     
     
       18. The machine-readable medium of  claim 16 , wherein the one or more first volumes contain an application program. 
     
     
       19. The machine-readable medium of  claim 16 , wherein the one or more first working copies are received by rebooting. 
     
     
       20. The machine-readable medium of  claim 16  further including data that cause the machine to perform operations comprising:
 initiating a boot process out of a local memory; 
 sending a first request for a boot information to the NC server; 
 receiving the boot information from the NC server; 
 sending a second request for a boot image to the NC server based on the boot information; 
 receiving the boot image from the NC server; and 
 executing the boot image. 
 
     
     
       21. The machine-readable medium of  claim 16  further including data that cause the machine to perform operations comprising:
 generating a write request; and 
 redirecting the write request to the one or more second volumes at the NC server. 
 
     
     
       22. The machine-readable medium of  claim 16  further including data that cause the machine to perform operations comprising:
 sending a read request to the NC server; 
 determining if the read request is associated with the one or more second working copies; 
 sending the read request to retrieve first data from the one or more second volumes if the read request is associated with the one or more second working copies; and 
 sending the read request to retrieve second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       23. A machine-readable storage medium storing data that, when accessed by a machine, cause the machine to perform operations, comprising:
 copying one or more first working copies from one or more first volumes to one or more second volumes; 
 enabling of modifying of the one or more first working copies on a NC server by rebooting a first NC client to generate one or more second working copies; 
 receiving the one or more second working copies generated by the first NC client; and 
 replacing the one or more first volumes having the one or more first working copies with the one or more second volumes having the one or more second working copies that include the one or more first working copies that have been modified at the first NC client that are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       24. The machine-readable medium of  claim 23 , wherein the one or more first volumes contain an operating system. 
     
     
       25. The machine-readable medium of  claim 23 , wherein the one or more first volumes contain an application program. 
     
     
       26. The machine-readable medium of  claim 23 , wherein the enabling of the modifying is performed by rebooting the first NC client. 
     
     
       27. The machine-readable medium of  claim 23  further including data that cause the machine to perform operations comprising:
 receiving a first request for a boot information from the first NC client; 
 sending the boot information to the first NC client; 
 receiving a second request for a boot image from the NC client; and 
 sending the boot image to the NC client. 
 
     
     
       28. The machine-readable medium of  claim 23  further including data that cause the machine to perform operations comprising:
 receiving a write request to modify the one or more first volumes from the NC client; and 
 storing the information associated with the write request in the one or more second volumes. 
 
     
     
       29. The machine-readable medium of  claim 23  further including data that cause the machine to perform operations comprising:
 receiving a read request; 
 determining if the read request is associated with the one or more second working copies; 
 retrieving first data from one or more second volumes if the read request is associated with the one or more second working copies; and 
 retrieving second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       30. The machine-readable medium of  claim 23  further including data that cause the machine to perform operations comprising:
 determining if the one or more second working copies are to be deleted; and 
 marking the one or more second working copies for deletion during a subsequent reboot of the first NC client if the one or more second copies are be deleted. 
 
     
     
       31. An apparatus, comprising:
 means for receiving one or more first working copies of one or more first volumes; 
 means for modifying the one or more first working copies to generate one or more second working copies, wherein the means for modifying includes 
 means for generating a write request; and 
 means for redirecting the write request to a NC server over a network, wherein information associated with the write request is 
 to be stored in one or more second volumes at the NC server, wherein the one or more second working copies that include the one or more first copies that have been modified at the first NC client are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       32. The apparatus of  claim 31 , wherein the one or more first volumes contain an operating system. 
     
     
       33. The apparatus of  claim 31 , wherein the one or more first volumes contain an application program. 
     
     
       34. The apparatus of  claim 31 , wherein the one or more first working copies are received by rebooting. 
     
     
       35. The apparatus of  claim 31 , further comprising
 means for initiating a boot process out of a local memory; 
 means for sending a first request for a boot information to the NC server; 
 means for receiving the boot information from the NC server; 
 means for sending a second request for a boot image to the NC server based on the boot information; 
 means for receiving the boot image from the NC server; and 
 means for executing the boot image. 
 
     
     
       36. The apparatus of  claim 31 , further comprising:
 means for generating a write request; and 
 means for redirecting the write request to the one or more second volumes at the NC server. 
 
     
     
       37. The apparatus of  claim 31 , further comprising:
 means for sending a read request to the NC server; 
 means for determining if the read request is associated with the one or more second working copies; 
 means for sending the read request to retrieve first data from the one or more second volumes if the read request is associated with the one or more second working copies; and 
 means for sending the read request to retrieve second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       38. An apparatus, comprising:
 means for copying one or more first working copies from one or more first volumes to one or more second volumes; 
 means for enabling of modifying of the one or more first working copies on a NC server by rebooting a first NC client to generate one or more second working copies; 
 means for receiving the one or more second working copies generated by the first NC client; and 
 means for replacing the one or more first volumes having the one or more first working copies with the one or more second volumes having the one or more second working copies that include the one or more first working copies that have been modified at the first NC client that are to be used by one or more second NC clients at a subsequent booting from the NC server, wherein the NC server, the first NC client, and the one or more second NC clients are coupled via a network. 
 
     
     
       39. The apparatus of  claim 38 , wherein the one or more first volumes contain an operating system. 
     
     
       40. The apparatus of  claim 38 , wherein the one or more first volumes contain an application program. 
     
     
       41. The apparatus of  claim 38 , wherein the enabling of the modifying is performed by rebooting the first NC client. 
     
     
       42. The apparatus of  claim 38 , further comprising:
 means for receiving a first request for a boot information from the first NC client; 
 means for sending the boot information to the first NC client; 
 means for receiving a second request for a boot image from the NC client; and 
 means for sending the boot image to the NC client. 
 
     
     
       43. The apparatus of  claim 38 , further comprising:
 means for receiving a write request to modify the one or more first volumes from the NC client; and 
 means for storing the information associated with the write request in the one or more second volumes. 
 
     
     
       44. The apparatus of  claim 38 , further comprising:
 means for receiving a read request; 
 means for determining if the read request is associated with the one or more \ second working copies; 
 means for retrieving first data from one or more second volumes if the read request is associated with the one or more second working copies; and 
 means for retrieving second data from the one or more first volumes if the read request is associated with the one or more first working copies. 
 
     
     
       45. The apparatus of  claim 38 , further comprising:
 means for determining if the one or more second working copies are to be deleted; and 
 means for marking the one or more second working copies for deletion during a subsequent reboot of the first NC client if the one or more second copies are be deleted.

Description:
This application is a continuation of U.S. patent application Ser. No. 09/420,503, filed on Oct. 18, 1999 now U.S. Pat. No. 7,089,300. 
    
    
     COPYRIGHT NOTICE 
     Contained herein is material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction of the patent disclosure by any person as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights to the copyright whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to network computing. More particularly, the invention relates to the provision, administration, and maintenance of an operating system in a net-booted environment. 
     2. Description of the Related Art 
     Most organizations currently employ local area networks (LANs) of thick clients, e.g., personal computers. While this represents an improvement over the disconnected computing environments of a decade earlier, many limitations still exist. In current LAN environments, each client computer has its own local copy of operating system software, application programs, and user customizations to the desktop environment. Typically there is no centralized mechanism for maintaining a consistent system configuration in such a computing environment. Consequently, individual user workstations often get out-of-sync with each other as one or more users upgrade to newer versions of the operating system, upgrade their application programs, or install application programs that were not part of the original system configuration. Additionally, in this type of uncontrolled, decentralized environment, the operating system of a client computer can easily become corrupted. This is especially true with the Microsoft® Windows® 95, 98 and NT operating systems where user modification of a single system file can have undesirable consequences and require significant downtime. For example, editing the Windows Registry file could render a client computer unusable thereby requiring reinstallation of the computer&#39;s operating system software and all the application programs. 
     In view of the foregoing, it should be apparent that administration and maintenance of current computing environments is complex and time consuming. Therefore, what is needed is a reliable computing environment that can be maintained more easily and at a lower cost. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and apparatus are described for providing a reliable and maintainable operating system in a net-booted environment. According to one embodiment, a network computer (NC) system including an NC server and multiple NC clients is managed by an NC client causing the remainder of the NC clients that are subsequently booted to receive operating system software that is configured differently than that currently in effect by replacing one or more system volumes on the NC server containing the operating system software with one or more different system volumes. 
     Other features and advantages of the invention will be apparent from the accompanying drawings and from the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  is a simplified block diagram that conceptually illustrates a network computer system according to one embodiment of the present invention. 
         FIG. 2  is a block diagram of a digital processing system which may be used in accordance with one embodiment of the present invention. 
         FIG. 3  is a flow diagram illustrating processing that occurs on an NC client and an NC server to accomplish a net-boot of the NC client according to one embodiment of the present invention. 
         FIG. 4  is a flow diagram illustrating how NC client write requests directed to the system volume are handled according to one embodiment of the present invention. 
         FIG. 5  is a flow diagram illustrating how NC client read requests directed to the system volume are handled according to one embodiment of the present invention. 
         FIG. 6  is a simplified block diagram illustrating an exemplary hierarchical directory structure that may be used by an NC server according to one embodiment of the present invention. 
         FIG. 7  is a flow diagram illustrating NC system administration processing according to one embodiment of the present invention. 
         FIG. 8  is a simplified block diagram illustrating two NC systems coupled via the Internet. 
         FIG. 9  is a block diagram that conceptually illustrates NC client interaction with a SplitOS according to one embodiment of the present invention. 
         FIG. 10  is a block diagram that conceptually illustrates the structure of a shadow system volume according to one embodiment of the present invention. 
         FIG. 11  is a block diagram that conceptually illustrates the structure of a shadow system volume according to another embodiment of the present invention in which a banding feature is employed. 
         FIG. 12  is an example of a machine-readable medium that may be assessed by a digital processing system, such as an NC client or an NC server, according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A method and apparatus are described for providing a reliable and maintainable operating system in a net-booted environment. Broadly stated, embodiments of the present invention seek to provide a fault-tolerant, self-repairing, and remotely maintainable operating system for the clients in a net-booted environment. According to one embodiment of the present invention, a network computer (NC) system maintains a copy of the operating system that cannot be corrupted by ordinary users of the NC system. Additionally, the NC system may preserve user customizations, such as preferences, by maintaining individual, user, storage areas. When an NC client boots from the network and accesses a stored copy of the operating system from an NC server, the user&#39;s preferences are dynamically merged with the system environment provided to the NC client. Advantageously, since, the user&#39;s desktop preferences and other customized settings are all preserved from session to session and supplied to the NC client as it boots from the network, the user may login to any NC client on the network and have the same user experience. According to another embodiment, a network administrator can upgrade every NC client in the NC system to a new version of the operating system by simply replacing a single file on the NC server. Further, according to another feature of the present invention, the network administrator can perform such an upgrade remotely from any NC client of the NC system. Advantageously, in this manner, NC system administration and maintenance costs are kept low as compared to a typical network of thick clients that each has a local copy of the operating system that must be replaced. 
     In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form. 
     The present invention includes various steps, which will be described below. The steps of the present invention may be performed by hardware components or may be embodied in machine-executable instructions, which may be used to cause a general-purpose or special-purpose processor or logic circuits programmed with the instructions to perform the steps. Alternatively, the steps may be performed by a combination of hardware and software. 
     The present invention may be provided as a computer program product which may include a machine-readable medium having stored thereon instructions which may be used to program a computer (or other electronic devices) to perform a process according to the present invention. The machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing electronic instructions. Moreover, the present invention may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer (e.g., a server) to a requesting computer (e.g., a client) by way of data signals embodied in a carrier wave or other propagation medium via a communication link (e.g., a modem or network connection). Accordingly, herein, a carrier wave shall be regarded as comprising a machine-readable medium. 
     Importantly, while embodiments of the present invention will be described with reference to the Mac® operating system (OS) software and NetBoot technology on a Mac OS X Server, the method and apparatus described herein are equally applicable to other types of servers and operating systems, such as Microsoft® Windows® 95/98, Windows NT, Windows 2000, Windows CE, AIX, UNIX®, Linux, and the like. Consequently, the techniques described herein are thought to be generally useful in connection with remote bootstrapping of client systems in a variety of operating environments and networking environments. 
     Terminology 
     Before describing an exemplary environment in which various embodiments of the present invention may be implemented, some terms that will be used throughout this application will briefly be defined. 
     The terms “boot,” “booting,” “bootstrap,” and “bootstrapping” generally refer to the process of starting-up a computer, which typically involves loading operating system software. 
     An “image” refers to an electronic representation of an individual disk or a portion thereof. 
     The term “file system” generally refers to the logical structures and software routines used to control access to and from the storage on a storage medium, such as a hard disk system. 
     An “operating system” refers to a program that manages a computer&#39;s internal functions and provides a means to control the computer&#39;s operations and file system. Examples of operating systems include: MacOS, Windows 95/98, Windows NT, Windows 2000, Windows CE, AIX, UNIX, and Linux. 
     “Personal computer” generally refers to a computer system equipped with system, utility, application software, and/or input/output devices. Importantly, as used herein, the term “personal computer” is intended to refer collectively and individually to stand-alone Macintosh® computers, Apple® computers, IBM® Personal Computers, IBM PC-compatible computers, Amiga computers, and others, such as Commodore that are no longer manufactured and those yet to be manufactured. 
     The term “thick client” generally refers to a computer system, such as a personal computer (PC), that includes a hard drive or other local storage medium. Traditionally, such computer systems boot and execute application programs from the local storage medium. 
     A “thin client” generally refers to a disk-less computer system that relies upon external means, such as a server, to supply it with an operating system and application programs. 
     As used herein, the terms “network computer client” or “NC client” generally refer to a client (thick or thin) that boots by accessing a copy of the operating system over a network. As such, an NC client is not required to be disk-less. 
     The terms “network computer server” or “NC server” generally refer to a computer system that services requests of NC clients. For example, an NC server may provide access to a copy of the operating system to an NC client in response to a boot request. 
     A “network computer system” or “NC system” refers to a network including one or more NC clients and one or more NC servers. 
     In the context of this application, the term “volume” generally refers to a fixed amount of storage on a storage medium, such as a disk or tape. In some instances, however, the term may be used as a synonym for the storage medium itself. However, it is possible for a single storage medium to contain more than one volume or for a volume to span more than one storage medium. 
     Network Computer System Overview 
     In order to obtain the benefits of low-cost administration, all storage of application programs and operating system software for an NC system is preferably on the NC server. This doesn&#39;t mean the NC clients have no mass storage, but rather that the NC clients boot over the network by accessing a stored copy of the operating system from the NC server. Additionally, when NC clients want to run an application, they access it from the NC server. Advantageously, in this manner, an application may be upgraded by simply replacing the old version of the application with a new version on the NC server. Then, the next time an NC client requests the application, the NC client will receive the new version. 
       FIG. 1  is a simplified block diagram that conceptually illustrates an NC system  100  according to one embodiment of the present invention. In this example, the NC system  100  includes an NC client  150  coupled to an NC server  170  via a data communication link  140 , such as a 10, 100, or 1000 megabit/second Ethernet link. While according to one embodiment, the NC client  150  is a Macintosh computer or iMac™ computer and the NC server  170  is a Mac OS X Server, the NC client  150  and/or the NC server  170  may alternatively represent one or a combination of the devices/systems described below with reference to  FIG. 2 . 
     The NC server  170  includes one or more system volumes  174 , one or more application volumes  176 , a user registry  178 , non-persistent client-specific data  184 , and persistent user data  186 . The system volumes  174  include a protected, read-only, master copy of the operating system software. The application volumes  176  include copies of various application programs for use by the NC client  150 . According to one embodiment, the user registry  178  is a database of authorized users, user passwords, NC client hardware addresses, such as Ethernet Media Access Control (MAC) addresses, and NC client network addresses, such as Internet Protocol (IP) addresses. In an AppleTalk network environment or the like, the user registry  178  may comprise the AppleShare Registry. The non-persistent client-specific data  184  represents temporary data storage that is typically preserved only for the duration of a user session on a particular NC client. The persistent user data  186  represents long-term data storage for user information that is desirable to retain between user sessions, such as preferences, browser bookmarks, and other desktop environment customizations. 
     The NC server  170  also includes a boot server process  172 , a server software management process  180 , and a user environment process  182 , each of which may include hard-wired circuitry or machine-executable instructions or a combination thereof. Furthermore, at least a portion of such hard-wired circuitry and/or machine-executable instructions may be shared between a combination of the boot server process  172 , the server software management process  180 , and the user environment process  182 . In one embodiment, at least one storage area/memory (e.g., a machine-readable medium) having appropriate routines and/or data stored therein coupled to at least one processor is utilized, at least in part, to implement one or a combination of the boot server process  172 , the server software management process  180 , and the user environment process  182 . 
     According to one embodiment, the boot server process  172  manages access to and from the system volumes  174  and the application volumes  176 . Additionally, the boot server process  172  performs server-side bootstrapping processing. In one embodiment, the boot server process  172  may include conventional Bootstrap Protocol (Bootp) server processing that waits for NC clients to appear on the network in accordance with Request For Comments (RFC) 951, Bill Croft, John Gilmore, Bootstrap Protocol, RFC 951, September 1985, RFC 2132, and uses the standard extensions format. As described further below, when the boot server process  172  receives a boot request from the NC client  150 , the boot server process  172  may provide the NC client  150  with a network address, such as an Internet Protocol (IP) address, the address of the NC server  170 , and the name of a file to be loaded into memory and executed. This first phase of the bootstrapping process is described by RFC 951 as the “address determination and bootfile selection” phase. The second phase of the boot strapping process involves the file transfer of the bootfile (also referred to as a boot image) by way of the Trivial File Transfer Protocol (TFTP), the Simple File Transfer Protocol (SFTP), the File Transfer Protocol (FTP), or the like. Further details regarding the particular information exchanged during these two phases will be described below. 
     In one embodiment, to facilitate remote NC system administration, such as the installation of new system or application software, the boot server process  172  may serve application and system images that exist in the NC client&#39;s folder at the time of bootstrapping as a read-write file. In this manner, a user having proper access privileges on the NC system, such as an NC system administrator, may create a read-write file from any NC client in the NC system, modify the read-write file, and subsequently upgrade the NC system by simply replacing the system and/or application volumes on the NC server with the modified file. 
     In one embodiment the server software management process  180  manages access to and from the non-persistent client-specific data  184 . For example, at the conclusion of a user session on an NC client, the server software management process  180  may provide data that is to be preserved between user sessions to the user environment management process  182  and reinitialize the client-specific storage area associated with the NC client for use by the next user. According to one embodiment, the server software management process  180  performs self-repair functionality at two levels, automatic and administrator commanded. For example, the NC server  170  may be configured to automatically replace the shadow volume at every boot of a NC client  150 . This insures that every time that NC client boots it will have a complete, functional operating system regardless of any changes any connected user has made to their system. In the event that a user performs some action which would damage their operating system in a standard desktop environment, the server software management process  180  repairs that damage at the next boot. 
     According to one embodiment, the user environment management process  182  tracks and maintains the persistent user data  186  to insure that changes the user has made during the current session will be persistent at the next logic. For example, upon termination of a user session, preferences, desktop items, and various other information representing changes made by the user during the user session are copies to a user-specific storage location on the NC server  170 . Subsequently, at the user&#39;s next login, from the same or different NC client, the user environment management process  182  will retrieve the data from the corresponding user-specific storage location and return it to the NC client thereby allowing the user to login to any NC client of the NC system  100  and have the same user experience. 
     In one embodiment, the administration tool  188  facilitates NC system administration by automating certain file manipulations that are common for software installation and configuration changes. The administration tool  188  is described further below. 
     While for purposes of illustration, the boot server process  172 , the server software management process  180 , the user environment process  182 , and the administration tool  188  are shown as part of a single NC server  170 , in alternative embodiments, they may be distributed in whole or in part across multiple server computer systems. Additionally, the system volumes  174 , the application volumes  176 , the user registry  178 , the non-persistent client-specific data  184 , and the persistent user data  186  may be independently distributed across multiple server computer systems. 
     The NC client  150  includes one or more system volume images  160  and one or more application volume images  162 . The outlines of the system volume images  160  and the application volume images  162  are shown with dotted outlines because preferably only representations of the content of the corresponding NC server volumes are stored in random access memory of the NC client  150  rather than copies of the actual underlying data and files of the corresponding NC server volumes. 
     The NC client also includes a file system  152 , a block device driver  154 , a network stack  156 , and a network device driver  158 , each of which may include hard-wired circuitry or machine-executable instructions or a combination thereof. Furthermore, at least a portion of such hard-wired circuitry and/or machine-executable instructions may be shared between a combination of the file system  152 , the block device driver  154 , the network stack  156 , and the network device driver  158 . In one embodiment, at least one storage area/memory (e.g., a machine-readable medium) having appropriate routines and/or data stored therein coupled to at least one processor is utilized, at least in part, to implement one or a combination of the file system  152 , the block device driver  154 , the network stack  156 , and the network device driver  158 . 
     The file system  152  represents logical structures and software routines that are used to control access to and from a local storage medium, such as a hard disk system. Since the NC client  150  may not have a local mass storage device, the file system  152  may actually control access to and from a remote storage medium with or without knowledge that this is occurring. According to one embodiment, the file system  152  operates as if the contents of the system volumes  160  are, in fact, contained on a local hard drive and the file system&#39;s read and write requests are redirected at a lower level of the operating system. In an alternative embodiment, the file system  152  itself may be given knowledge regarding the need to read and write to the network rather than to a local hard drive. 
     The block device driver  154  services file system read and write requests to the system volumes  160 . In one embodiment, the block device driver  154  appears to the file system  152  to be a standard hard drive device driver. However, in reality, the block device driver  154  may be configured to service the read and write requests of the file system  152  by accessing the NC server  170 . As will be discussed further below, in one embodiment, one or more shadow volumes, may be created for the NC client  150  and stored with the non-persistent client-specific data  184  for the purpose of storing user preferences and/or changes to the operating system. Therefore, some mechanism is needed to direct reads and writes to the appropriate volume, e.g., the shadow volumes or the system volumes  174 . According to one embodiment, the block device driver  154  has knowledge of the separate shadow volumes and system volumes  174  and redirects read and write requests to the appropriate volume. Alternatively, server-side logic may perform the redirection locally. 
     The network stack  156  represents logical structures and software routines that are used to control access to and from the data communication link  140 . In this example, the network stack  156  employs the services of the network device driver  158  to transform data into electrical signals that are appropriate for the specific type of physical media, such as Ethernet. 
     Exemplary Digital Processing System 
       FIG. 2  is a block diagram of a digital processing system which may be used in accordance with one embodiment of the present invention. For example, the digital processing system  200  shown in  FIG. 2  may be used as an NC client, an NC server, or other server computer system, such as an NT server. The digital processing system  200  may be interfaced to external systems through a network interface  268 . It will be appreciated that the network interface  268  may be considered as part of the digital processing system  200 . The network interface  268  may be an analog modem, an ISDN modem, a cable modem, a token ring interface, a satellite transmission interface, a wireless interface, or other interface(s) for providing a data communication link between two or more digital processing systems. 
     The digital processing system  200  includes a processor  252 , which may represent one or more processors and may include one or more conventional types of such processors, such as Motorola PowerPC processor, an Intel Pentium (or x86) processor, etc. A memory  254  is coupled to the processor  252  by a bus  256 . The memory  254  may be a dynamic random access memory (DRAM) and/or may include static RAM (SRAM). The processor may also be coupled to other types of storage areas/memories (e.g., cache, Flash memory, disk, etc.), which could be considered as part of the memory  254  or separate from the memory  254 . 
     The bus  256  further couples the processor  252  to a display controller  258 , an optional mass memory  262 , the network interface  268 , and an input/output (I/O) controller  264 . The mass memory  262  may represent a magnetic, optical, magneto-optical, tape, and/or other type of machine-readable medium/device for storing information. For example, the mass memory  262  may represent a hard disk, a read-only or writeable optical CD, etc. The display controller  258  controls in a conventional manner a display  260 , which may represent a cathode ray tube (CRT) display, a liquid crystal display (LCD), a plasma display, or other type of display device. The I/O controller  264  controls I/O device(s)  266 , which may include one or more keyboards, mouse/trackball or other pointing devices, magnetic and/or optical disk drives, printers, scanners, digital cameras, microphones, etc. 
     It will be appreciated that the digital processing system  200  represents only one example of a system, which may have many different configurations and architectures, and which may be employed with the present invention. For example, Macintosh and Intel systems often have multiple busses, such as a peripheral bus, a dedicated cache bus, etc. On the other hand, a network computer, which may be used as a digital processing device of the present invention, may not include, for example, a hard disk or other mass storage device, but may receive routines and/or data from a network connection, such as the network interface  268 , to be processed by the processor  252 . Similarly, a Web TV system, which is known in the art, may be considered to be a digital processing system of the present invention, but such a system may not include one or more I/O devices, such as those described above with reference to I/O device(s)  266 . Additionally, a portable communication and data processing system, which may employ a cellular telephone and/or paging capabilities, may be considered a digital processing system which may be used with the present invention. 
     The processor  252  may execute one or more routines to redirect read and write requests from the file system  152  of the NC client to an appropriate volume on the NC server. Such routines may be stored in the mass memory  262 , the memory  264 , and/or another machine-readable medium accessible by the digital processing system  200 . According to one embodiment of the present invention, a network computer (NC) system maintains a copy of the operating system in the mass memory  262  (and/or the memory  254 ) that cannot be corrupted by ordinary users of the NC system. Additionally, the NC system may preserve user customizations, such as preferences, by maintaining individual, user, storage areas in the mass memory  262  (and/or the memory  254 ). When an NC client boots from the network and accesses the operating system from an NC server, the user&#39;s preferences are dynamically merged with the system environment provided to the NC client. Advantageously, since, the user&#39;s desktop preferences and other customized settings are all preserved from session to session and supplied to the NC client as it boots from the network, the user may login to any NC client on the network and have the same user experience. According to another embodiment, a network administrator can upgrade every NC client in the NC system to a new version of the operating system by simply replacing a single file on the NC server. Further, according to another feature of the present invention, the network administrator can perform such an upgrade remotely from any NC client of the NC system. Advantageously, in this manner, NC system administration and maintenance costs are kept low as compared to a typical network of thick clients that each has a local copy of the operating system that must be replaced. 
     Net-Booting Overview 
     Having briefly described an exemplary environment in which the present invention may be employed, exemplary net-boot processing will now be described with reference to  FIG. 3 . Providing a reliable, fault-tolerant and maintainable operating system for all NC clients in a net-booted environment is an important component in insuring the successful implementation of such as system. NC clients have no operating system internally. Therefore, they depend on reliably retrieving a complete operating system from the network to boot and continue operations. 
     The NC system environment and the net-booting process described herein are intended to provide the needed reliability. The net-booting process generally breaks down into an address determination and bootfile selection phase, a file transfer phase, a RAM boot phase and a system boot. The address determination and bootfile selection phase is represented by steps  350  through  375 , the file transfer phase includes steps  380  and  385 , and the RAM boot phase is represented by steps  390  and  395 . Briefly, for administrative and maintenance purposes, preferably only the NC server  320  has a copy of the master read-only operating system image and NC clients boot according to the net-booting process described below. Since rebooting an NC client restores the NC client to a standard, useable state, it is impossible for a user without proper access privileges to make an NC client unbootable. Consequently, this NC system architecture and net-booting approach greatly simplifies NC client administration and provides a high level of reliability for the NC clients. 
     The first phase of the net-booting processing begins at step  350 . After the NC client  310  has powered on, the NC client  310  starts the address determination and bootfile selection phase by initiating the boot process out of a local read-only memory (ROM). This may include executing power-on self tests, acquiring device information, and performing any other functions necessary to give the NC client  310  a basic identify. 
     At step  355 , the NC client  310  connects to the network and asks for additional information to be provided to it that will allow it to boot further. According to one embodiment, the request for additional information takes the form of a Bootp request. In alternative embodiments, the Dynamic Host Configuration Protocol (DHCP) may be employed. 
     At step  360 , the NC server  320  receives the boot request and determines if the request is from a known NC client. For example, the NC server  320  may search the user registry  178  for the NC client&#39;s hardware address. 
     If the NC client  310  is unknown to the NC server  320 , then an IP address is allocated for the NC client  310  at step  370  and registration processing is performed. In order to allow the NC server  320  to recognize the NC client  310  next time it boots, information regarding the NC client  310  may be stored in the user registry  178 . For example, the NC client&#39;s hardware address can be marked as known in the user registry  178  and the IP address allocated can be associated in the user registry with the NC client&#39;s hardware address. User registration processing may include creating a user for this NC client  310 , e.g., by adding the user to the user registry  178 , and creating a private system file for the user. 
     If the NC client  310  is known to the NC server  320 , then at step  365  information regarding the NC client  310 , such as its IP address may be retrieved from the user registry  178 . 
     At step  375 , boot information is returned to the NC client  310 . The boot information may include, among other things, the IP address of the NC client  310 , the IP address of the NC server  320 , the name of the file to be loaded into the NC client&#39;s memory and executed, and the names and locations of shadow volumes, if any. 
     The second phase of the bootstrapping process, file transfer of the bootfile, begins at step  380 . According to one embodiment, the NC client  310  sends a file transfer request to the NC server  320  specifying the bootfile identified in the NC server&#39;s Bootp reply. At step  385 , the NC server  320  responds by initiating the transfer of the boot image. Upon receipt at the NC client  310 , the boot image is stored in a local RAM of the NC client  310 . 
     After the NC client  310  has received the boot image from the NC server  320 , the RAM boot phase begins at step  390 . During the RAM boot phase, the NC client  310  begins to execute the boot image out of the local RAM. According to one embodiment, the boot image is a Macintosh ROM image that performs additional machine initialization, and creates a Macintosh environment. In alternative embodiments, the boot image may create other operating environments, such as Windows 95/98, Windows NT, Windows 2000, etc. In one embodiment, the block device driver  154  may be included as part of the boot image. Alternatively, the block device driver  154  may be part of the NC client&#39;s ROM. 
     Finally, at step  395 , the NC client  310  mounts the remote system and application volumes  174  and  176 . Other boot processing (not shown) may include a system boot phase in which the setting up of the operating environment is completed and the virtual memory subsystem is initialized. At this point, a login may be presented on the NC client  310 . Based upon the user information, the user environment management process  182  may move all the components that are specific to this user, including preferences, to the user&#39;s system environment. 
     System Read/Write Redirection 
     As indicated above, the NC client  150  may or may not have a local storage medium, such as a hard disk system. Therefore, in one embodiment, the block device driver  154  may redirect read and write requests received from the file system  152  to a remote storage medium on the NC server  170 , for example. 
       FIG. 4  is a flow diagram illustrating how NC client write requests directed to the system volumes  160  are handled according to one embodiment of the present invention. In one embodiment, the steps described below may be performed under the control of a programmed processor, such as processor  252 . However, in alternative embodiments, the steps may be fully or partially implemented by any programmable or hardcoded logic, such as Field Programmable Gate Arrays (FPGAs), TTL logic, or Application Specific Integrated Circuits (ASICs), for example. 
     According to the embodiment depicted, at step  410 , the file system  152  generates a write request directed to the system volumes  160 . The write request is received by the block device driver  154  and redirected by the block device driver  154  at step  420  by translating it into a write request directed to the user&#39;s shadow volume on the NC server  170 . At step  430 , the NC server  170  stores information associated with the write request in the shadow volume associated with the NC client  150 . In this manner, the file system  152  need not be aware that attempted modifications to the system volumes  160  are recorded instead in a client-specific shadow volume residing on the NC server  170 . 
     In alternative embodiments, however, the file system  152  may be configured to recognize that write requests should be directed to the network interface  268 . In these embodiments, the file system  152  may be configured to bypass the block device driver and interface directly with the network stack  156 . 
     In other embodiments, the block device driver  154  may retain knowledge that writes are to be redirected to the NC server  170 , but may not be aware of the existence of the shadow volume. Therefore, the block device driver  154  will issue write requests to the NC server  170 , but will issue these requests to the system volumes  174  rather than the shadow volume. In this situation, logic on the NC server  170  will redirect the write requests received from the NC client  150  to the appropriate shadow volume. 
     According to yet another alternative embodiment, the NC server  170  may maintain separate copies of the operating system software in its entirety for each user. However, this would likely have the effect of increasing complexity of the NC server  170  and could potentially dramatically increase the storage requirements of the NC server  170 . 
     Referring now to  FIG. 5 , NC client read request processing will now be described according to one embodiment of the present invention. In one embodiment, the steps described below may be performed under the control of a programmed processor, such as processor  252 . However, in alternative embodiments, the steps may be fully or partially implemented by any programmable or hardcoded logic, such as Field Programmable Gate Arrays (FPGAs), TTL logic, or Application Specific Integrated Circuits (ASICs), for example. 
     In the embodiment depicted, it is assumed that the shadow volume contains only those portions of the operating system that have been modified by the user rather than a complete copy of the operating system as modified. The various options regarding the granularity of the portions written to the shadow volume are discussed below. 
     At any rate, according the present example, at step  510 , the file system  152  generates a read request directed to the system volumes  160 . At step  520 , the read request is received by the block device driver  154  and a determination is made whether the read request specifies a portion of the operating system that has been modified by the user or whether the read request specifies a portion of the operating system that remains unchanged. If the read request corresponds to a portion of the operating system that has not been modified by the user, the processing continues with step  530 . However, if the read request corresponds to a portion of the operating system that has been previously modified by the user, then processing continues with step  540 . 
     At step  530 , the block device driver directs the NC server  170  to retrieve the information associated with the read request from the system volumes  174 . 
     At step  540 , the block device driver directs the NC server  170  to retrieve the information associated with the read request from the user&#39;s shadow volume. 
     In this manner, the file system  152  need not be aware of the particular mechanism used to coordinate user modifications with the original operating system as contained in the system volumes  174 . 
     In alternative embodiments, rather than having the block device driver  154  keep track of which portions of the operating system that have been modified by the user, such a tracking mechanism may be implemented centrally on the NC server  170 . In this case, the NC server  170  would make the determination of step  520  and provide the appropriate read responses in steps  530  and  540 . 
     In yet another embodiment, the NC server  170  may maintain separate copies of the operating system in its entirety for each user, including any user-specific modifications. In this case, neither the block device driver  154  nor the NC server  170  would need to track which portion(s) of the operating system contain user modifications. Rather, the portion of the user-specific copy of the operating system corresponding to the read request may simply be returned in response to the read request. 
     Exemplary Server Directory Structure 
       FIG. 6  is a simplified block diagram illustrating the layout of an exemplary hierarchical directory structure that may be used by an NC server according to one embodiment of the present invention. 
     According to the embodiment depicted, a hard drive  610  of the NC server  170  or other mass storage device associated with the NC server  170  includes an NC folder (directory)  620 . Within the NC folder  620  are an NC admin folder  630  and an NC shared data folder  640 . The NC admin folder  630  is preferably inaccessible to ordinary users that do not have proper access privileges and includes a read-only, master operating system image  650 . 
     The NC shared data folder  640  includes a shared operating system image  660 , a boot image  670 , and a clients folder  680 . The shared operating system image  660  is a read-write version of the read-only master operating system image  650  and may be mounted by the NC client  150  as part of step  395 . The boot image  670  is downloaded and executed by the NC client  150  after the first phase of the bootstrapping process in order to create an operating environment on the NC client  150 , such as a Macintosh or Windows environment. 
     The clients folder  680  is an area that may be used to store non-persistent client-specific information, such as modifications to the shared operating system  660 . In this example, the NC clients are numbered from  1  to N and the clients folder  680  includes a folder for each NC client. For example, an NC # 1  folder  690  is an area for storing client-specific information, such as a shadow image  695 , corresponding to NC client # 1 . As described above, the shadow image  695  preferably contains only portions of the shared operating system image  660  that have been modified by the user. However, the shadow image  695  may be a user-specific copy of the shared operating image  660  in its entirety. 
     Network Computer System Administration 
     As described above, according to one embodiment, NC system administration is facilitated by a feature of the boot server process  172  that serves application and system images to the NC client  150  as a read-write file if such images exist in the NC client&#39;s folder. Thus, a user of the NC client  150  having proper access privileges is provided with the ability to upgrade the NC system by replacing the existing images being served to the NC clients with modified versions containing, for example, new system or application software or configuration changes. 
       FIG. 7  is a flow diagram illustrating NC system administration processing according to one embodiment of the present invention. According to this example, at step  710 , the NC server  170  receives an administrator logic request from the NC client  150 . At step  720 , the NC server  170  performs administrator login processing to verify the user has appropriate access privileges on the NC system  100 . Assuming the user has appropriate access privileges, processing continues with step  730 . At step  730 , one or more shared images (e.g., shared operating system image  660  and/or a shared application image) are copied to the NC client&#39;s folder on the NC server  170 . At step  740 , editing of the one or more shared image copies (the working copies) is enabled. According to one embodiment, this is accomplished by simply rebooting the NC client  150  as discussed above. Alternatively, the attributes associated with the working copies may be modified in some other manner so as to make them editable by the user. In any event, at step  750 , the user may add software and/or make configuration changes to the working copies. Finally, the NC system is updated at step  760  by replacing the one or more shared images currently being served to NC clients with the working copies. Advantageously, in this manner, there is no need to log users out to insure that changes have been propagated across all the images. Instead, changes become accessible to a NC client the next time that NC client is booted thereby allowing all connected users to easily complete whatever tasks they are working on without impeding NC system administration. 
     According to one embodiment, steps  730 ,  740 , and  760  may be provided as part of the administration tool  188 . The first execution of the administration tool  188  may accomplish step  730  by copying the shared images to the appropriate NC client folder. After the copies are complete, the administration tool  188  may automatically restart the NC client  150 , which will boot up with read-write access to the working copies. 
     At this point, the network administrator is free to add software and/or make configuration changes. When the network administrator has completed his/her changes, the administration tool  188  can be run for a second time at which point the network administrator may be presented with the option of either committing (saving) or discarding the changes to the working copies. 
     If the administrator chooses to discard the changes, the administration tool  188  marks the working copies for deletion. Note that immediate deletion of the working copies is not desirable because the NC client  150  is still using the working copies. Rather, it is preferable to remove the working copies that are marked for deletion during a subsequent boot of the NC client  150 . In one embodiment, the administration tool  188  automatically restarts the NC client  150  thereby causing the removal of the working copies and causing the NC client  150  to boot from the shared images. 
     If the administrator chooses to commit the changes, the administration tool  188  can immediately replace the shared images with those of the working copies that have been edited which makes the updates immediately available to any NC client that subsequently boots. 
     Advantageously, the administration tool  188  allows the network administrator to remotely modify the shared images on the NC server  170  from an NC client without having to access the NC server  170  directly. Additionally, use of the administration tool  188  allows the administrator to update the NC system  100  without having to know about or directly manipulate the files on the NC server  170 . 
       FIG. 8  is a simplified block diagram illustrating two NC systems  810  and  820  coupled via the Internet  805 . It is contemplated that the NC system configuration process described above with reference to  FIG. 7  may also be useful in connection with the reconfiguration of remote NC systems. For example, the administration tool  188  may be run from any of NC clients  812 ,  814 , or  816  to install a new application program on local NC system  810  that is desired by the users of the local NC system  810  as well as by the users of NC clients  822 ,  824 , and  826  of remote NC system  820 . After completing the steps described above for installation on the local NC system  810 , the administration tool  188  running on NC system  810  may replicate the modified shared images to the remote NC system  820 . 
     Split Operating System 
       FIG. 9  is a block diagram that conceptually illustrates NC client interaction with a SplitOS  920  according to one embodiment of the present invention. According to the example depicted, the SplitOS  920  of the NC server  170  contains a read-only core system volume image  922  and a read-write user system volume image  924 . 
     The core system volume  922  preferably contains those parts of the system that do not need to be written back to during system operation. One goal of the core system volume  922  is to provide all the system components that are mandatory for system operation. By separating these essential components from the user system volume  924  and protecting them as read-only, an additional level of stability is provided to the NC system  100  since a user will be unable to delete or move items that are essential to system operation. 
     The user system volume  924  contains all the user-configurable system components, including preferences and all the system additions installed by application software, such as application-installed extensions and libraries. Additionally, the user system volume  924  may contain applications that cannot be run from an AppleShare server and/or other system components that do not function on a read-only volume. 
     Preferably, the NC server  170  also creates a shadow system volume  930  for each connected NC client. The shadow system volume  930  shadows the user system volume  924  by storing modifications that are made to the user system volume  924 . In alternative embodiments, the NC server  170  may provide a separate user system volume  924  for each connected NC client. 
     As described above, according to one embodiment, the shadow system volume  930  is used by the block device driver  154  of the NC client  150  to implement a “copy-on-write” storage scheme in which modifications (writes) directed to the user system volume  930  are instead copied to the shadow system volume  930 . In one embodiment, the shadow system volume  930  is not visible to the user. Consequently, the user system volume  924  will appear to be the location where all writes are directed. For example, if a user modifies a preference, that preference will appear to be written to the preference file located in the preferences folder on the user system volume  924 . 
     As indicated by the directional arrows along the connections between the core system volume  922 , the user system volume  924 , and the shadow system volume  930  and the NC client  910 , data may be read from each of the core system volume  922 , the user system volume  924 , and the shadow system volume  930 ; however, data may only be written to the shadow system volume  930 . 
     Shadow System Volume 
       FIG. 10  is a block diagram that conceptually illustrates the structure of a shadow system volume  1020  according to one embodiment of the present invention. In this example, the shadow system volume  1020  is a complete copy of the system volume  1010  with any user-modifications incorporated therein. Therefore, the disk space used by the shadow system volume  1020  will be approximately the same as that used by the system volume  1010 . 
     Banding 
       FIG. 11  is a block diagram that conceptually illustrates the structure of a sparse shadow system volume  1120  according to another embodiment of the present invention in which a banding feature is employed. According to this embodiment, the sparse shadow system volume  1120  is written in band increments rather than as an entire file. A band is a predetermined number of blocks. For example, according to one embodiment bands are 128K (256 512-byte blocks). In alternative embodiments, the band size may be more or less. Using bands, the disk space used by the shadow volume  1120  will consist only of the actual data written (in band increments). 
     According to one embodiment of the banding feature, the inherent one-to-one block mapping in copy-on-write images may be replaced with a table or other data structure that maps a band of the primary file to a corresponding band in the shadow file. Logic may be included in the block device driver  154 , for example, to break up requests into the largest contiguous chunks possible. In this manner, both reads and writes can span non-contiguous band boundaries. 
     The main motivation for banding is to reduce disk space requirements of the NC client shadow system images. According to one embodiment, the reduction is achieved by only storing those bands which have actually been written to. An exemplary band table  1122  is a simple array allocated at initialization. Entries in the table are assigned BAND_NONE until the corresponding band is written to, at which point the next available band in the shadow file is assigned. In order to encourage contiguous blocks on the NC server&#39;s file system, in one embodiment, if bands are allocated during a write, the shadow file size is increased to the appropriate number of bands before the write request is sent. 
     Exemplary Machine-Readable Medium 
       FIG. 12  is an example of a machine-readable medium  1200  that may be accessed by a digital processing system, such as an NC client or an NC server, according to one embodiment of the present invention. Importantly, the actual memory that stores the elements shown in and described below with reference to  FIG. 12  may comprise one or more disks (which may, for example be magnetic, optical, magneto-optical, etc.), the memory  254  and/or the mass memory  262  described above with reference to  FIG. 2 , or a combination thereof. Additionally, one or more of the elements of the machine-readable medium  1200  may be stored at one digital processing system, such as an NC server, and downloaded or transmitted to another digital processing system, such as an NC client or another NC server. Furthermore, the elements described with reference to the machine-readable medium  1200  may, at some point in time, be stored in a non-volatile mass memory (e.g., a hard disk). Conversely, at other times, the elements of the machine-readable medium  1200  maybe dispersed between different storage areas, such as DRAM, SRAM, disk, etc. 
     According to one embodiment, the machine-readable medium  1200  is utilized, at least in part, to facilitate administration and maintenance of system and/or application volumes of an NC system in accordance with one or more methods of the invention. For example, the machine-readable medium  1200  may be associated with an NC server and include one or more routines for performing bootstrapping as discussed with reference to  FIG. 3  (the boot server program  1205 ), for performing system read and write processing as discussed with reference to  FIGS. 4 and 5  (the block device driver  1230 ), and/or for performing remote administration of the NC system  100  as discussed with reference to  FIG. 7  (the administration program). 
     While the block device driver  1230  is show as being separate from the boot image  1210  in this example, the block device driver may be provided as part of the boot image  1210  in alternative embodiments. 
     Alternative Embodiments 
     While the invention has been described with reference to specific embodiments and illustrative figures, those skilled in the art will recognize that the invention is not limited to the embodiments or figures described. In particular, the invention can be practiced in several alternative embodiments that provide net-booting and remote administration of an NC system. 
     Therefore, it should be understood that the method and apparatus of the invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting on the invention.

Metadata:
Filing Date: 20060710
Publication Date: 20110104
Grant Date: 20110104
Priority Date: 19991018
Inventors: BIRSE CAMERON STUART
STATTENFIELD KEITH
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F9/4416", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L67/34", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F9/4416", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L67/34", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 36942122