Multicast system and method for deploying multiple images simultaneously

A system, method and data structure for transmitting a first image including a first software and for transmitting a second image including a second software, wherein the first and second images include common file data. The server simultaneously transmits the common data to first and second destination devices via the shared network. The server is adapted to transmit the first file data to the first destination device via the shared network and the second file data to the second destination device via the shared network.

FIELD OF THE INVENTION

The invention generally relates to the duplication of volume images and, in particular, to simultaneous multicasting of two or more images by transmitting the common data of the images, the unique data of each image and the descriptive data of each image.

BACKGROUND OF THE INVENTION

Typically, volume images are large files which cannot be split up. A large scale deployment of these types of images using multicast technology requires that all clients receive the exact same image. If different images are to be applied to different clients, a separate multicast stream is required for each unique image to be provided to one or more clients. This requires substantial bandwidth and, in some respects, defeats the purpose of multicast in the first place.

SUMMARY OF THE INVENTION

Employing the imaging format described in the co-pending patent applications noted here, the descriptive data (metadata) of an image is separated from the actual file data. Since the remaining actual file data is organized by file (instead of being organized by sector, like other imaging solutions), this imaging format can be used to implement a solution according to the invention for multicasting multiple images. Because the descriptive data for each image is relatively small, each client can download the descriptive data from the server via normal means such as unicasting (rather than multicasting). The server will keep a list of all the clients that have downloaded image descriptive data and will stream out (in one stream) all the file data that is required by any of the clients. Every client will receive a unique identifier for each file currently being multicast by the server. If the file is not listed in the previously received descriptive data for a particular client, then the particular client ignores it. Otherwise, it will receive and store the file based on the descriptive data. Once a client has received and stored all the files required to reconstruct the image, it will notify the server that it is finished so that the server will know when to stop streaming out certain file data. Thereafter, the client does not have to do anything more to restore the image at this point. The image is the collection of files. The individual files that it received constitute the image. The client need only place the files in the correct location. Preferably, while it is receiving the files, the client can store the files directly to their final location (unless it needs to do some processing of the received data such as decompression). Even then, the client can store the files in the right location as soon as it is done processing.

Since most images contain similar data with other images, another image can be added in the stream and only slightly increase the time required to transmit the images. For example, if Image1is made up of files A,B,C and image2is made up of A,B,D (for simplicity, consider sizeof(A)=sizeof(B)=sizeof(C)=sizeof(D)). If it takes 1 unit of time to send each component, for image1it would take time=3 and for image2it would take time=3. For images1and2sequentially it would take time=6 (t(1)+t(2)) whereas for images1and2at the same time according to the invention it would take time=4. (t(A)+t(B)+t(C)+t(D)).The less in common images have, the longer it will take all the clients to receive their entire image. Alternatively, one or more multicast streams can be added. The server automatically tries to balance between client restore time and network bandwidth usage and can be optimized for either.

In one form, the invention is a system for transmitting a first image including a first software and for transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The system comprises a server; a first destination device; a second destination device; and a shared network linking the server to the first and second destination devices. The server is adapted to simultaneously transmit the common data to the first and second destination devices via the shared network. The server is adapted to transmit the first file data to the first destination device via the shared network and the second file data to the second destination device via the shared network.

In another form, the invention is a method for transmitting a first image including a first software to a first destination device and for transmitting a second image including a second software to a second destination device, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The method comprises simultaneously transmitting the common data to the first and second destination devices; transmitting the first file data to the first destination device; and transmitting the second file data to the second destination device.

In another form, the invention is a client side system for receiving a first transmitted image including a first software from a server, the server also transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data, wherein the server transmits the first image including the first software and the second image including the second software in a single combined image stream from which the first image and/or the second image can each be re-created by imaging, wherein the server is adapted to transmit via the shared network to the first destination device descriptive data of the first image identifying the common data and first file data, wherein the server is adapted to transmit via the shared network to the first and second destination devices the common data and file data including the first file data and the second file data. The client side system comprises a destination device including a link to the server; software for receiving the descriptive data of the first image; and software for receiving the combined image stream; and software responsive to the received descriptive data of the first image for storing the common file data and the first file data.

In another form, the invention is a client side system for use on a destination device for receiving a first transmitted image including a first software from a server, the server also transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data, wherein the server transmits the first image including the first software and the second image including the second software in a single combined image stream from which the first image and/or the second image can each be re-created by imaging, wherein the server is adapted to transmit via the shared network to the first destination device descriptive data of the first image identifying the common data and first file data, wherein the server is adapted to transmit via the shared network to the first and second destination devices the common data and file data including the first file data and the second file data. The client side system comprises software for receiving the descriptive data of the first image; software for receiving the combined image stream; and software responsive to the received descriptive data of the first image for storing the common file data and the first file data.

In another form, the invention is a client side method in which a destination device receives a first transmitted image including a first software from a server, wherein the server also transmits a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data, wherein the server transmits the first image including the first software and the second image including the second software in a single combined image stream from which the first image and/or the second image can each be re-created by imaging, wherein the server is adapted to transmit via the shared network to the first destination device descriptive data of the first image identifying the common data and first file data, wherein the server is adapted to transmit via the shared network to the first and second destination devices the common data and file data including the first file data and the second file data. The client side method comprises receiving the descriptive data of the first image; and receiving the combined image stream; and storing the common file data and the first file data in response to the received descriptive data of the first image.

In another form, the invention is a server side system for transmitting a first image including a first software and for transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The system comprises a server linked to first and second destination devices via a shared network. The server is adapted to simultaneously transmit the common data to the first and second destination devices via the shared network. The server is adapted to transmit the first file data to the first destination device via the shared network and the second file data to the second destination device via the shared network.

In another form, the invention is a server side method for transmitting a first image including a first software and for transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The method comprises simultaneously transmitting the common data to the first and second destination devices via the shared network; and transmitting the first file data to the first destination device via the shared network; and transmitting the second file data to the second destination device via the shared network.

In another form, the invention is a data transmission method of transmitting a first image including a first software and a second image including a second software into a single combined image stream from which the first image and/or the second image can each be re-created by imaging onto a destination device, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The method comprises transmitting descriptive data of the first image identifying the common data and first file data; transmitting descriptive data of the second image identifying the common data and second file data; and transmitting the common data and file data including the first file data and the second file data.

In another form, the invention is a modulated data signal having a data structure stored thereon including a first image including a first software and including a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The data structure comprises a first field including the common data; a second field including first file data; and a third field including second file data.

In another form, the invention is a computer readable medium storing instructions for use on a destination device for receiving a first transmitted image including a first software from a server, the server also transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data, wherein the server transmits the first image including the first software and the second image including the second software in a single combined image stream from which the first image and/or the second image can each be re-created by imaging, wherein the server is adapted to transmit via the shared network to the first destination device descriptive data of the first image identifying the common data and first file data, wherein the server is adapted to transmit via the shared network to the first and second destination devices the common data and file data including the first file data and the second file data. The instructions comprise software for receiving the descriptive data of the first image; software for receiving the combined image stream; and software responsive to the received descriptive data of the first image for storing the common file data and the first file data.

In another form, the invention is a computer readable medium storing instructions for use on a server for transmitting a first image including a first software and for transmitting a second image including a second software, wherein the first and second images include common file data, wherein the first image includes first file data and wherein the second image includes second file data which is different from the first file data. The instructions comprises software for linking the server to first and second destination devices via a shared network; software for adapting the server to simultaneously transmit the common data to the first and second destination devices via the shared network; and software for adapting the server to transmit the first file data to the first destination device via the shared network and the second file data to the second destination device via the shared network.

DETAILED DESCRIPTION OF THE INVENTION

Referring first toFIG. 1, a block diagram of an image server storage system according to the prior art is illustrated. In general, reference character1100refers to a image server store having a plurality of disk images1102-1118separately and independently stored on CRM. Many of these images may have common data. For example, images1102-1106correspond to versions A, B and C of the same program (image1), respectively. As another example, images1108-1112correspond to versions A, B and C of another program (image2). As another example, images1114-1118correspond to versions A, B and C of another program (image3). However, each image is separately stored so that it can be transmitted to a destination device such as a destination device #1through destination device #N.

The image server store1100is selectively linked to the plurality of destination devices #1through #N via a shared network such as a local area network (LAN), wide area network (WAN) or the Internet. This linking, as indicated by arrows1120, may be a physical interconnection such as a hardware connection or a fiber optic line. In addition or alternatively, this linking may be a wireless interconnection such as a radio frequency (RF) or infrared (IR) transmission. The purpose of this linking is to allow a selected one or more of the images1102-1118to be imaged from the image server store1100to a selected destination device. For example, if image1102of image1version A is to be loaded onto destination device #2, image1102would be copied to destination device #2via link1120-2. If image1104of image1version B is to be loaded onto destination device #1, image1104would be copied to destination device #1, via link1120-1. If image1118of image3version C is to be loaded onto destination device #N, image1118would be copied to destination device #N via link1120-N. Thus, this setup allows any one or more images1120-1118to be selectively copied to any one or more destination devices #1through #N via link1120.

As noted above, one disadvantage of the prior art system illustsrated inFIG. 1is that a large amount of bandwidth (BW) is needed in order to transmit multiple images simultaneously to a plurality of destination devices. This is because a separate link1120is required to transmit each image so that the sum of the bandwidth BW required is approximately the sum of the bandwidth needed for each channel to separately transmit each image. For example, if each image of 450 megabytes (MB) in size will be transmitted over approximately 100 seconds, each image would require 4.5 Mbps of bandwidth. Thus, 9×4.5 Mbps or 40.5 Mbps of bandwidth would be needed to simultaneously transmit all nine (9) images from the server store1100to the separate destination devices #1-#9.

Referring next toFIG. 2, a block diagram of an image server storage system according to the invention is illustrated wherein combined disk images are stored on an image server store1200having an integrated or combined image1202separately and independently stored on a computer readable medium (CRM). Each integrated image is a combination of various images which share common file data, as described in detail in co-pending U.S. patent application Ser. No. 10/172,953, filed Jun. 17, 2002. entitled IMAGE SERVER STORE SYSTEM AND METHOD USING COMBINED IMAGE VIEWS and co-pending U.S. patent. application Ser. No. 10/173,297 filed Jun. 17, 2002, entitled COMBINED IMAGE VIEWS AND METHODS OF CREATING IMAGES., incorporated herein by reference.

In this example, integrated image1202is a combination of versions A, B and C of image1and versions A, B and C of image2and versions A, B and C of image3, each of which may be different image editions of the same software program. Common data is only copied once into the integrated image. File data common to versions A, B and C of images1,2and3would only appear once within the integrated image1202. Thus, the integrated image includes a header, descriptive data (metadata files) for versions1A through3C, file data files specific to versions1A to3C, offset tables for versions1A through3C, common data shared by all versions and a signature. Similarly, other integrated images, not shown, may be part of the image server store1200. In addition, the server store1200need not have an integrated image and, instead, can have separate files of the common and specific data.

Each integrated image1202is separately stored so that the image or selected portion of the image, as noted below, can be transmitted simultaneously to the destination devices. In particular, the image server store1200is selectively linked to a plurality of destination devices #1through #N. This linking, as indicated by arrows1206, may be a physical interconnection such as a hardware connection or a fiber optic line. In addition or alternatively, this linking may be a wireless interconnection such as an RF or IR transmission. The purpose of this linking is to allow a selected one or more or part of one or more of the image1202or other images on the server store to be transmitted simultaneously from the image server store1200to selected destination devices. In fact, the data is provided sequentially and can be received by multiple destination devices simultaneously so that all the devices can simultaneously receive the data.

For example, if image1102of image1version A is to be loaded onto destination device #2, the header, common data, offset table1A, metadata1A, file data specific to1A and signature (all part of image1102) must be copied to destination device #2via link1206. If image1104of image1version B is to be loaded onto destination device #1, the header, common data, offset table1B, metadata1B, file data specific to1B and signature (all part of image1104) must be copied to destination device #1via link1206. If image1118of image3version C is to be loaded onto destination device #N, the header, common data, offset table3C, metadata3C, file data specific to3C and signature (all part of image1118) must be copied to destination device #N via link1206. Thus, for all three images to be copied to the three different devices (#1, #2and #N), common data must be provided. According to the invention the common data may be simultaneously transmitted to all three different devices (#1, #2and #N). As a result, less bandwidth in needed to transmit the three different images to the three different devices and the images can be transferred faster than in the example ofFIG. 1.

In one embodiment, all data is sent sequentially so that descriptive data (e.g., header, offset table, metadata and signature) would be sent first followed by the common data and the specific data (in any order). In the prior example, the information may be sent in the following sequence: the header, offset table1A, metadata1A, offset table1B, metadata1B, offset table3C, metadata3C, signature, common data, file data specific to1A, file data specific to1B, and file data specific to3C.

Device #2would receive and store the header, offset table1A, metadata1A, signature, common data and file data specific to1A. Device #1would receive and store the header, offset table1B, metadata1B, signature, common data and file data specific to1B. Device #N would receive and store the header, offset table3C, metadata3C, signature, common data, and file data specific to3C.

Another scenario which is contemplated is round robin multicasting where common and specific data is continuously, sequentially transmitted and retransmitted and devices receive the data when the next cycle of transmission occurs.

This round robin multicasting may be varied depending on the requests for software to be transmitted. For example, a plurality of devices may request images1A and1B and the server would continue to repeatedly deliver a stream of data including the common data, data specific to1A and data specific to1B. During this transmission, one or more additional devices may request image2B. As a result, the server would add data specific to2B to each cycle of transmission and would repeatedly deliver a stream of data including the common data, data specific to1A, data specific to1B and data specific to2B.

It is also contemplated that in any and all scenarios some or all data may be sent simultaneously over the same or separate channels. For example, the descriptive data may be transmitted separately to each destination device via channel1208in response to a specific request from a device. Simultaneously, the common data and file specific data would be transmitted via a separate channel1206. After a destination device receives the descriptive data from channel1208, it would download the corresponding data from channel1206. As an example, suppose server1200supplies images1A,1B,1C,2A,2B,2C,3A,3B and3C. On channel1206, server1200would sequentially, repeatedly transmit the following: common data, data specific to1A, data specific to1B, data specific to1C, data specific to2A, data specific to2B, data specific to2C, data specific to3A, data specific to3B and data specific to3C. Also, suppose device #2requests a copy of image1A. Server1200would provide via link1208to device #2the following descriptive data: header, offset table1A, metadata1A and signature. Device #2would then connect to channel1206to wait for the next cyclic transmission of the common data and file data specific to1A as identified by the descriptive data. Device #2would receive and store the common data and the file data specific to1A when the next cyclic transmission occurs.

Channel1206may in fact be two channels, one which carries common data retransmitted over and over again and one channel which carries file specific data from a plurality of files which sequentially transmitted over and over again. Also, channel1206may in fact be multiple channels, several channels which carry part or all the common data retransmitted over and over again at varying time intervals and rates and one or more channels which carry file specific data from a plurality of files which sequentially transmitted over and over again.

Thus, this configuration allows any one or more images1102-1118to be selectively, simultaneously copied to any one or more destination devices #1through #N via link1206with substantially less bandwidth.

The invention makes it easier for the server1200to link with more destination devices over low bandwidth connections. (whereas before every new destination device would require additional bandwidth). According to the invention, only the data that is unique to a new image being requested or the delta to the image being requested needs to be added to the transmission cycle. For example, suppose each of the images1102-1118includes 350 MB of common filed data and 100 MB of unique data to be transferred over 100 seconds so that a bandwidth of 450 MB/100 sec times nine images or 40.5 MBps of bandwidth would be required for the nine images to be transmitted by the prior art system ofFIG. 1. In contrast, the system ofFIG. 2would transmit the 350 MB of common data and 900 MB of unique data and would only require 350 MB/100 sec plus 900 MB/100 sec or 12.5 MBps of bandwidth to transmit all nine images.

An example of a descriptive data structure (metadata files) which may be provided is as follows:

FIG. 3is a block diagram of an image server according to the invention including a master data index which includes file hashes and compression information.

FIG. 4is a block diagram of a compressed image file content.

Referring next toFIG. 5, operation of the system according to the invention is illustrated. The server1200transmits the first image including the first software and the second image including the second software in a single combined image stream1206from which the first image and/or the second image can each be re-created by imaging. In particular, the server is adapted to transmit first descriptive data to the first destination device via the shared network N. As noted above, the first descriptive data identifies the common data and first file data of the first image. In addition, the server1200is adapted to transmit second descriptive data to the second destination device via the shared network. As noted above, the second descriptive data identifies the common data and second file data of the second image.

From the client perspective, the first destination device receives the first descriptive data via link1208which defines the common data and the first file data of the first image. Similarly, the second destination device receives the second descriptive data via link1208which defines the common data and the second file data of the second image.

As illustrated inFIG. 5, it is contemplated that different channels may be employed to transmit the descriptive data and the common data. Thus, separate arrows1206and1208are used inFIG. 5to illustrate this. In addition, a separate channel1210may be employed to transmit information (request/notification) from the destination devices to the server. However, it is also contemplated that these separate channels may be integrated into a one or more channels having multiple subchannels or that all the data and information may be multiplexed over a single stream.

As shown inFIG. 5, the server multicasts the common data, the first file data, the second file data, . . . , and the Nth file data simultaneously to the first, second, . . . , N destination devices, respectively. Multicasting means the process of sending the various data and information being transmitted simultaneously to more than one destination (e.g., device) on a network.

It is also contemplated that, separate from the multicasting, the server directly transmits the first descriptive data to the first destination device, the second descriptive data to the second destination device, and so on via link1208. This direct transmission is the process of sending the descriptive data to one destination (e.g., device) at a time. Alternatively, the descriptive data may be transmitted by multicasting.

In order for the server1200to know what information and data to transmit, it maintains a list1212of destination devices and images to be transmitted to the destination devices on the list. Depending on the list, the server1200multicasts common data and file data corresponding to the images to be transmitted to the destination device on the list.

For example, if the first destination device sends a request to the server1200or otherwise indicates to the server that it wants to download the first image, the server will add the first destination device requiring the first image to the list. Similarly, if the second destination device sends a request to the server or otherwise indicates to the server that it wants to download the second image, the server will add the second destination device requiring the second image to the list.

Similarly, if the Nth destination device sends a request to the server or otherwise indicates to the server that it wants to download the Nth image, the server will add the Nth destination device requiring the Nth image to the list.

As a result, the server multicasts the common data, the first file data, the second file data and the Nth file data to the first destination device, second destination device and the Nth destination device. Each data or subpacket of data is transmitted with a unique identifier which is part of the descriptive data so that each destination device is able to identify the data that it requires.

The first descriptive data previously received by the first destination device includes the unique identifiers of the common data and first file data of the first image. The first destination device uses these unique identifiers to identify the portions of the multicast which include the common data and the first file data and stores only the common data and first file data as indicated by their unique identifiers. Thus, the first destination device receives the common data, the first file data and the second file data. The other destination devices function similarly to receive their images.

When the first destination device has received the common data and the file data corresponding to the first descriptive data, it provides a notification via channel1210to the server. In particular, when the first destination device has received all the common data and first file data of the image, so that it can restore the first software from the first image, it provides a first notification to the server1200. The server, in response to the first notification, removes the first destination device from the list. The server will discontinue multicasting the file data of the first image, unless another destination device on the list has requested the first image. Thus, the server's response to the first notification depends on the remaining destination devices and the images required that remain on the list. The remaining destination devices and their interaction with the server are similar to the first destination device. Once a destination device receives all the data of a particular descriptive data, it reconstructs the image corresponding to the particular descriptive data.

It is contemplated that the server may transmit a plurality of multicast streams including common and/or descriptive data and that the server selects a number of multicast streams as a function of destination device restore time and as a function of total bandwidth of the streams being transmitted.

Thus, the system of the invention employs a method for transmitting a first image including a first software to a first destination device and for transmitting a second image including a second software to a second destination device. The common data is simultaneously transmitted to the first and second destination devices. The first file data is transmitted to the first destination device and the second file data is transmitted to the second destination device.

A method according to the invention includes transmitting the first image including the first software and the second image including the second software in a single combined image stream from which the first image and/or the second image can each be re-created by imaging. In particular, first descriptive data of the first image identifying the common data and first file data is transmitted to the first destination device via link1208. Similarly, second device descriptive data of the second image identifying the common data and second file data is transmitted to the second destination device via link1208. In response, the first destination device receives via stream1206the common data and the first file data as defined by the first descriptive data previously transmitted to the first destination device. In addition, the second destination device receives via stream1206the common data and the second file data as defined by the second descriptive data previously transmitted to the second destination device.

In addition, the system and method of the invention provide the ability to prioritize clients. The above describes a two-client scenario. However, the invention is applicable to two or more clients and clients may be prioritized. As additional clients come on-line, the order of files being transmitted may be modified based on the priority of clients that are on-line at any particular time. This priority can be established by a list of files according to priority, a list of clients according to priority, a list of client locations accoridng to priority or any other means for establishing a priority.

Alternatively or in addition, a client may indicate its priority to the server. In any case, the server is configured to sequentially transmit the file data in a sequence defined by the established priority.

Prioritizing clients and/or files means thtat the server controls which clients are have all their files first. For example, a new client may come online and the new client may have need for unique data and may have a priority that is higher than other clients on line. In this example, the server can be configured to broadcast the unique data of the new client first, before the unique data of other on-line clients. This scenario becomes particulary useful when serving a large number of client (e.g., 100 or more clients) and a new client comes on-line that requires an image so that it can get done faster than the other clients. In this latter scenario, the server can broadcast the unique data required by the new client first before broadcasting the unique data of the other clients (e.g., the remaining 100 or more clients).

In one embodiment, each destination device comprises a client side system which receives a first transmitted image including a first software from the server. The server also transmits a second image including a second software, such that the first and second images include common file data. The client side system includes a destination device including a link to the server, software S1for receiving the descriptive data of the first image, software S2for receiving the combined image stream, and software S3responsive to the received descriptive data of the first image for storing the common file data and the first file data. In addition, the client side system includes software S4for restoring the image. Thus, a client side method comprises receiving the descriptive data of the first image and receiving the combined image stream; and storing the common file data and the first file data in response to the received descriptive data of the first image.

According to one aspect of the invention, a server side system transmits a first image including a first software and transmits a second image including a second software. The server is adapted to simultaneously transmit the common data to the first and second destination devices via the shared network. In addition, the server is adapted to transmit the first file data to the first destination device via the network and the second file data to the second destination device via the network. Thus, a server side method comprises simultaneously transmitting the common data to the first and second destination devices via the network; and transmitting the first file data to the first destination device via the network; and transmitting the second file data to the second destination device via the network.

According to one aspect of the invention, a data transmission method is provided for transmitting a first image including a first software and a second image including a second software into a single combined image stream from which the first image and/or the second image can each be re-created by imaging onto a destination device. The method comprises transmitting descriptive data of the first image identifying the common data and first file data; transmitting descriptive data of the second image identifying the common data and second file data; and transmitting the common data and file data including the first file data and the second file data. As noted above, the transmitting of the descriptive data may be on a different channel that the transmitting of the common data and the file data. As noted above, the transmitting of the common data and the file data may be sequentially transmitting the common data, the first file data and the second file data. As a result, the modulated data signal has a data structure stored thereon including a first image including a first software and including a second image including a second software. For example, the data structure may include a first field including the common data, a second field including first file data and a third field including second file data.

FIG. 6shows one example of a general purpose computing device in the form of a computer130. In one embodiment of the invention, a computer such as the computer130is suitable for use in the other figures illustrated and described herein. Computer130has one or more processors or processing units132and a system memory134. In the illustrated embodiment, a system bus136couples various system components including the system memory134to the processors132. The bus136represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus.

The computer130typically has at least some form of computer readable media. Computer readable media, which include both volatile and nonvolatile media, removable and non-removable media, may be any available medium that can be accessed by computer130. By way of example and not limitation, computer readable media comprise computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. For example, computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by computer130. Communication media typically embody computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media. Those skilled in the art are familiar with the modulated data signal, which has one or more of its characteristics set or changed in such a manner as to encode information in the signal. Wired media, such as a wired network or direct-wired connection, and wireless media, such as acoustic, RF, infrared, and other wireless media, are examples of communication media. Combinations of the any of the above are also included within the scope of computer readable media.

The system memory134includes computer storage media in the form of removable and/or non-removable, volatile and/or nonvolatile memory. In the illustrated embodiment, system memory134includes read only memory (ROM)138and random access memory (RAM)140. A basic input/output system142(BIOS), containing the basic routines that help to transfer information between elements within computer130, such as during start-up, is typically stored in ROM138. RAM140typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit132. By way of example, and not limitation,FIG. 6illustrates operating system144, application programs146, other program modules148, and program data150.

The computer130may also include other removable/non-removable, volatile/nonvolatile computer storage media. For example,FIG. 6illustrates a hard disk drive154that reads from or writes to non-removable, nonvolatile magnetic media.FIG. 6also shows a magnetic disk drive156that reads from or writes to a removable, nonvolatile magnetic disk158, and an optical disk drive160that reads from or writes to a removable, nonvolatile optical disk162such as a CD-ROM or other optical media. Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive154, and magnetic disk drive156and optical disk drive160are typically connected to the system bus136by a non-volatile memory interface, such as interface166.

The drives or other mass storage devices and their associated computer storage media discussed above and illustrated inFIG. 6, provide storage of computer readable instructions, data structures, program modules and other data for the computer130. InFIG. 6, for example, hard disk drive154is illustrated as storing operating system170, application programs172, other program modules174, and program data176. Note that these components can either be the same as or different from operating system144, application programs146, other program modules148, and program data150. Operating system170, application programs172, other program modules174, and program data176are given different numbers here to illustrate that, at a minimum, they are different copies.

A user may enter commands and information into computer130through input devices or user interface selection devices such as a keyboard180and a pointing device182(e.g., a mouse, trackball, pen, or touch pad). Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are connected to processing unit132through a user input interface184that is coupled to system bus136, but may be connected by other interface and bus structures, such as a parallel port, game port, or a Universal Serial Bus (USB). A monitor188or other type of display device is also connected to system bus136via an interface, such as a video interface190. In addition to the monitor188, computers often include other peripheral output devices (not shown) such as a printer and speakers, which may be connected through an output peripheral interface (not shown).

The computer130may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer194. The remote computer194may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to computer130. The logical connections depicted inFIG. 6include a local area network (LAN)196and a wide area network (WAN)198, but may also include other networks. LAN136and/or WAN138can be a wired network, a wireless network, a combination thereof, and so on. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and global computer networks (e.g., the Internet).

When used in a local area networking environment, computer130is connected to the LAN196through a network interface or adapter186. When used in a wide area networking environment, computer130typically includes a modem178or other means for establishing communications over the WAN198, such as the Internet. The modem178, which may be internal or external, is connected to system bus136via the user input interface184, or other appropriate mechanism. In a networked environment, program modules depicted relative to computer130, or portions thereof, may be stored in a remote memory storage device (not shown). By way of example, and not limitation,FIG. 6illustrates remote application programs192as residing on the memory device. It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used.

The invention may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other devices. Generally, program modules include, but are not limited to, routines, programs, objects, components, and data structures that perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.