Patent Publication Number: US-8539038-B2

Title: Method and system for preloading resources

Description:
RELATED APPLICATIONS 
     This application is a continuation patent application of allowed U.S. patent application Ser. No. 10/319,424, filed Dec. 12, 2002, which is projected to issue as U.S. Pat. No. 7,895,261 on Feb. 22, 2011, which claims the benefit of U.S. Provisional Patent Application No. 60/341,079, filed Dec. 12, 2001, the benefits of which are hereby claimed under 35 U.S.C. §120 and 119(e) respectively. The provisional application and the patent are incorporated herein by reference. 
    
    
     BACKGROUND 
     In the past, when a user desired to change versions of software, the user was required to go to a store, purchase the new software, and install the new version on the user&#39;s computer. 
     Today, some software, including some upgrades, is distributed over the Internet. If the software can be packaged in a small executable, a software vendor may choose to distribute the software over the Internet. Using this model, a user can browse to a vendor&#39;s Website, pay for software, and then download the software. 
     This model has problems when the software requires a lot of disk space or when the user has an Internet connection with relatively low bandwidth. For example, to download a CD&#39;s worth of software (650 Megabytes) using a computer having a 28.8 kilobits per second (Kbs) connection to the Internet would take over 50 hours to download. Even with a 512 Kbs connection, downloading 650 Megabytes of software would take almost three hours—assuming that the connection remained up and delivered its full bandwidth. 
     What is needed is an efficient way to provide the application to the user over the Internet. 
     SUMMARY 
     A method and system is provided which is directed a preloading resources for an application. Preloading the resources allows an application to run smoothly without consuming more resources than are needed by an application at any point during the execution. 
     According to one aspect of the invention, a determination is made as to what resources will be needed by an application. The resource list may be static or dynamic. 
     According to another aspect of the invention, application hints are used in generating the resources needed by the application. The application hints may indicate a state of the application. The resources that will be needed may be determined based on the state information. 
     According to another aspect of the invention, a preloader may load resources both while the application is executing and also when the application is not executing. The preloader process that determines which resources to load may be located on the client or on the server. 
     According to yet another aspect of the invention a prediction graph may be used to anticipate the resources that are likely to be needed by an application. State changes within the application may be used in generating the prediction graph. 
     According to a further aspect of the invention, parameters may be adjusted to fine tune the prediction graph. The parameters may be adjusted manually or automatically. A simulation tool may be used to simulate the behavior of the system. The simulation tool may tune itself iteratively until the system performs at a predetermined level of acceptability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-3  show components of an exemplary environment in which the invention may be practiced; 
         FIG. 4  illustrates using application hints to preload data; 
         FIG. 5  illustrates a process for retrieving and using resource information to preload resources; 
         FIG. 6  shows a process for receiving or generating resource lists associated with application hints; 
         FIG. 7  illustrates a process for using static resource lists to preload data; 
         FIG. 8  shows an exemplary resource name mapping table; 
         FIG. 9  illustrates a process for an out-of-app preloader; 
         FIG. 10  shows a process for in-app preloader execution; 
         FIG. 11  illustrates a process flow of an in-app preloader; 
         FIG. 12  shows a preloader system, 
         FIG. 13  illustrates a process to generate a prediction graph; 
         FIG. 14  shows a predictor using the prediction graph; and 
         FIG. 15  illustrates an iterative simulation/tuning loop for building a prediction graph by adjusting parameters, in accordance with aspects of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanied drawings, which form a part hereof, and which are shown by way of illustration, specific exemplary embodiments of which the invention may be practiced. The term “resource” is any data an application uses for execution. For example, a resource may be a particular portion of a file. The file may be a data file, a dynamic link library, an executable program, a component, and the like. 
     These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     Application Hints to Preload Data 
       FIG. 4  illustrates using application hints to preload data, in accordance with aspects of the invention. A preloader attempts to load resources before they are needed by an application. The preloader may run as a thread of an application, as part of an application&#39;s flow, for example as a function that is called periodically, and/or separate from the application. An application hint is used to indicate that a resource should be preloaded. The hint may include a list of files, such as a resource list, that should be preloaded. The hint may indicate the priority of the loading for the resource. For example, the application hint may indicate that a resource list should be loaded immediately, i.e., that the preloader should stop preloading what it is currently loading and begin loading resources from the resource list immediately. 
     Hints may arise in a variety of circumstances. For example, some electronic games have multiple levels or maps on which users play. In some games, these maps are changed periodically. At a certain point before the map is changed, a hint may be provided to a preloader indicating that the preloader should begin preloading resources for the next map. The hint may include a list of resources in the next map that the preloader should preload. 
     As another example, a user may pass a certain point in the game. For example, the user may enter a certain room that is close to a set of stairs that is leading up or down. When the user enters the room, a hint may be provided to a preloader indicating that resources from a lower or upper level should be loaded. This helps to ensure that the user does not wait for these resources to load, should the user decide to take the stairs. 
     In an application suite including a word processor and a spreadsheet, for example, a user may select a print menu. When the user selects the print menu, a hint may be provided to the preloader indicating that printer drivers and routines should be preloaded in case the user decides to print the document. Alternatively, if a user stops working with the word processor and begins working with the spreadsheet, a hint may be provided to the preloader indicating that the preloader should stop loading resources required for the word processor and begin loading resource that may be needed for the spreadsheet. As can be seen, hints may be used to indicate any status within an application in which resources are needed. 
     In one embodiment of the invention, the capability to indicate a hint may be provided in an API that interfaces between the application and the file system. The API may allow both the application and an external application to provide hints to the preloader. 
     For example, an administrator or creator of a game may decide to put a special monster in a particular part of the game universe. An application the administrator is using may send messages to APIs on user machines telling the APIs that they should use hints to preload certain resources if a user is near the place where the monster will be placed. The API may pass the hint to the user application or query a user application for the user&#39;s current position. The application may also send a resource list with its message to each API. The API may use the resource list to provide a hint and/or may pass the resource list to the application so that if the user is close to the monster&#39;s area, a hint may be provided to the preloader that includes the resource list. 
     As another example, an application might be keyed to the actual weather local to a user. When the user enters the application, the application may request the local weather. The application may then hint to a preloader that certain weather resources, such as texturing and rain routines, should be preloaded. 
     Resources may be loaded for a user&#39;s currently subscribed to content as well as non-currently subscribed content. For instance, preloading may be used too “trickle-download” large sets of data before a new application is released. By utilizing the available time to download content this helps to ensure that potential subscribers have the majority of bits for the new version/release/application, or other content before it is needed. Using this preloading scheme, the use of bandwidth may be effectively controlled. Preloading may also be used to send down marketing, ads, demo applications, and the like. Although the user has some control over the preloading (like on/off and cpu/memory/disk/network usage) these means of preloading are generally invoked by the publisher/provider. 
       FIG. 5  illustrates a process for retrieving and using resource information to preload resources, in accordance with aspects of the invention. In one embodiment of the invention, the preloader may load resources from a stack. There may be a stack for each priority level such that the next resource that is loaded will be the resource with the next highest priority level. Accordingly, a push of a lower priority resource onto a stack does not block a higher priority hint. When a hint is provided to the preloader, the preloader may push references to resources in a resource list associated with the hint onto the stack and adjust its stack pointer to point to the first resource in the hinted resource list. After a start block, the process flows to block  510  where using the stack the process retrieves information for the next resource to load. Moving to block  520 , the resource is preloaded. Transitioning to decision block  530 , a determination is made as to whether there are any resources left to preload. When there are still resources remaining to preload, the process returns to block  510 , otherwise, the process moves to a return block where it returns to processing other actions. 
     After the preloader has preloaded all the resources on the hinted resource list, the stack pointer may be popped and thereby point to the resource the preloader was preloading before the hint was received. Alternatively, the preloader may wait to finish loading a resource before beginning processing any of the resources listed in a hint resource list.  FIG. 6  shows a process for receiving or generating resource lists associated with application hints. After a start block, the process moves to block  610  where a resource list associated with a hint is received or generated (See  FIGS. 13-15  and related discussions for exemplary methods of generating a resource list). Moving to block  620 , the items are pushed onto the preloading stack. The process then returns to processing other actions. 
       FIG. 13  illustrates a process to generate a prediction graph, in accordance with aspects of the invention. A predictor may be used to predict what resources will be needed and be used in the generation of a resource list. The resource requests and resource hints received from applications during previous execution sessions (e.g. pre-release testing, or real usage sessions of the released application, or simulated usage driven by artificially intelligent agents (often called ‘bots’ instead) of human users) (block  1310 ) may be stored (block  1315 ) and later processed and combined using various algorithms to build a prediction graph. The prediction graph&#39;s nodes each represent an “application resource request state”, considered as being the sequence of resource requests (state transitions) that lead from the ‘origin’ of the graph (representing application startup, before any resources have been requested) to this particular node (block  1325 ). Each node in the graph may be tagged with a resource identifier or group of resource identifiers, or an application resource hint identifier, which describes the request or group of requests that the application made to transition from a previous state (node) to this present state (node) (block  1330 ). The prediction graph&#39;s edges (connections between nodes) each represent a prediction based on historical evidence, manual configuration or algorithmic speculation, that one application “resource request state” is transformed into another by moving from node to node along that edge. Each edge may be weighted by any combination of probability of request, time interval between requests, or other relevant data to indicate the strength of the prediction (likelihood) of that particular state transition (block  1335 ). The prediction graph is therefore directed (edges have a direction) and may be cyclic, acyclic, or a tree. Examples of algorithms used to combine and process the session lists into the prediction graph are those identifying exact or inexact common subsequences (including longest common subsequences), those utilizing Bayes&#39; Theorem, or those used to construct Markov Chains, Markov Models, Hidden Markov Models, or other relevant algorithms. An application may have very many of theses states and transitions so nodes and edges may be merged or removed according to various algorithms (usually degrading prediction quality to some degree) with the goal of constraining the size of the graph. The ‘session lists’ of resource requests used to build the prediction graph may be saved and gathered from the clients that run the application, or from the content servers that are satisfying the client&#39;s resource requests. 
       FIG. 14  shows a predictor using the prediction graph, in accordance with aspects of the invention. The resulting prediction graph may be used by a ‘predictor’ component during later runs of the application to predict the application&#39;s short or medium-term resource needs in a way which responds to changes in application state. The predictor represents the application&#39;s current ‘resource request state’ as a reference to a particular node in the prediction graph. The predictor tracks how this state changes as the application makes new resource requests and thereby “moves through the prediction graph” (block  1410 ) (e.g. If the application most recently requested resource “A” then the current state will be a reference to a node that identifies resource “A”. If this node has branches (predictions) to three nodes that in turn identify resources “C”, “D” and “E”, and the application now requests resource “D”, then the predictor considers that the application&#39;s “resource request state” has moved to the node found along the middle branch which identifies resource “D”. From time to time (e.g. after each application resource request or possibly less often) the predictor looks ahead in the graph from the ‘current state’ to identify resources that are most likely to be required next (block  1420 ). The predictor may build an ordered list of predicted resources by instituting a limited breadth-first or depth-first or other search of the graph from the ‘current state’ node (possibly taking measures to avoid revisiting cycles in the graph). The predictor may then eliminate from this list any resources that are already present on the local storage device (block  1430 ). The predictor may also communicate with other subsystems (e.g. local resource cache) to adjust information about any of the predicted resources that are already present on the local storage device (e.g. by adjusting their ‘least recently used’ timestamps, or tagging or reclassifying them in some way), in order to reduce the chances of those resources being purged from local storage in the immediate future, thus recognizing that these resources may have increased value as they have been mentioned in a prediction (block  1440 ). The predictor then feeds the resulting list of predicted resources to a preloader (block  1450 ). Therefore, instead of just loading the resources from requests from an application, the predictor will direct the preloader to load additional resources based on the prediction graph. The predictor may be more responsive to the short-term needs of applications with very large state domains or non-linear state traversal (e.g., a player wandering in any direction in a large game world). The predictor may therefore work in parallel with the system of large static resource lists described elsewhere. The predictor may assign priorities to its predictions that are above the priority of those static resource lists and below the priority of urgent (blocking) application requests. 
     As the number of application states and state-traversals is typically extremely large, it is unlikely that the ‘training data’ (lists of resource requests and hints gathered from previous execution sessions) used to build the prediction graph will be exhaustively complete (e.g. users may not have fully explored the game world or application feature set, or performed every permutation of every possible action). If, when using the prediction graph, the application happens to ‘step off the graph’ by requesting a resource that is not one of the current state&#39;s (node&#39;s) immediate predictions) then the predictor no-longer tracks the application&#39;s state transitions though the graph. When this situation occurs, the predictor may resort to a number of secondary alternative or backup prediction algorithms; e.g. the predictor may utilize a table that when indexed by resource identifier gives the identifiers of the most likely one (or several) resources that the application will request after requesting the indexed resource, regardless of application state. The predictor will continuously attempt to find a good node in the prediction graph at which to rejoin it, based on any relevant information. Examples of such information are locality of state, the application&#39;s most recent series of resource requests, and it&#39;s next several requests (The latter arrive over a period time, so the predictor may have to use the backup prediction algorithms multiple times until it obtains sufficient new data (new application requests) to find a good rejoin node.) For example, both the ‘request history before step-off’ and accumulating ‘request history since step-off’ sequences may be pattern-matched against sequences in the prediction graph in various ways in order to identify a good rejoin node. Searching and pattern matching may exploit locality of reference—e.g. prefer to search various branches just ahead of the “last known good” state of the application (just before it stepped off the graph) as a good rejoin point may be more likely to be found in this ‘close future’ part of the graph. Pattern matching and searching may spread out from the step-off node, both forwards and backwards through the graph until the predictor finds a good rejoin point. The algorithms used for this pattern matching may be similar to those used to process and combine the original training data to form the prediction graph. 
     The prediction graphs described may be treated as just another application resource. New prediction graphs can be generated from server logs and automatically sent to clients (as described in a (pending patent application) related patent entitled, METHOD AND SYSTEM FOR UPGRADING AND ROLLING BACK VERSIONS, (U.S. patent application Ser. No. 10/317,852, filed Dec. 11, 2002) U.S. Pat. No. 6,996,817, issued Feb. 7, 2006, which is hereby incorporated by reference), which transparently improves their preloading ability. 
     In another embodiment, individual clients may be able to modify their prediction graphs as the user drives the application. For example, when the predictor component ‘steps off the graph’ (fails to make a prediction) and later finds a good rejoin point, the predictor may add a branch from the step-off point to the rejoin point, in order to learn that transition (prediction) for subsequent sessions. The client application may also report such modifications to a central server for incorporation into the primary prediction graph. 
     The application may use one large prediction graph encompassing all of the training data (session lists), or several smaller prediction graphs, independently generated using groups or sections of session lists identified as being delimited by significant large-scale state changes in the application (e.g. a game application may use a separate prediction graph for each separate game map or game world it contains, as such game worlds may be very different to each other). 
       FIG. 15  illustrates an iterative simulation/tuning loop for building a prediction graph by adjusting parameters, in accordance with aspects of the invention. 
     The algorithms used to process and combine the session lists into the prediction graph may have many parameters that affect their behavior. Examples of such parameters include: InfluenceOfElapsedTimeInPredictionWeight, InfluenceOfDistanceFromStepOffPointWhenConsideringRejoinNodes, InfluenceOfNumberOfSequenceMismatchesWhenConsideringRejoinNodes, and many others. Many of these parameters are extremely sensitive. Tiny changes in the value can cause very large differences in the resulting prediction graphs. It may therefore difficult for a human to find the best (or even a good) set of parameter values to generate a prediction graph that makes good predictions while being as small (few nodes and edges) as possible. 
     In one embodiment, Graphical User Interface visualization tools are used to adjust the parameters and view the resulting prediction graph. In another embodiment, a degree of automation is used to help find good prediction graphs. A set of initial values for parameters is chosen (block  1505 ), either by a human or automatically (either randomized or remembered from previous sessions). A prediction graph is then generated from training data as described within this disclosure (block  1510 ). The prediction graph is then given to an analyzer component that tests its effectiveness. 
     The analyzer simulates the behavior of the system; i.e. the application making resource requests, the predictor component tracking state changes and making predictions, the preloader acquiring resources, and the local storage cache holding and purges acquiring resources (block  1515 ). The analyzer is a simulator so no actual resources are transferred, but the sizes of resources are known such that their transfer times over a network with certain average bandwidth can be calculated in order to know when preloaded resources actually arrive in the local storage cache. This helps to ensure correctly predicting cache misses. The analyzer uses session lists as test input and these are acquired in the same manner as the session lists that were used as training data to build the prediction graph (block  1520 ). The analyzer simulates the application making resource requests by making requests taken in order from a chosen session list (block  1530 ) The analyzer tests the effectiveness of the combined predictor component, prediction graph, and local store (purging algorithms) (block  1540 ). The analyzer then outputs performance data that indicate the effectiveness of the system (block  1550 ). In one embodiment, the performance data includes NumberOfCacheMisses, NurnberOfFailedPredictions, NumberOfCacheHitsInPredictions, NumberOfCacheHitsNotInCurrentPredictions, HighestNumberOfRetriesToFindARejoinNode, AverageNumberOfRetriesToFindARejoinNode, and many others. The analyzer may test the system using the actual training lists that were used to build the prediction graph, in which case the system is expected to do well (have few incorrect predictions and few cache misses). If the system does not do well then this indicates that the prediction graph may be too weak and more training data is needed or the creation algorithm parameters are not optimal and should be adjusted. The analyzer may also test the system using session lists that were never used as training data. These assess the ability of entire system (predictor, prediction graph, local cache purging) to cope with new ‘untrained’ sequences of application requests. More ‘failed predictions’ (‘step off the graph’) events are expected so these test quality of the backup prediction algorithms and the algorithms used to rind good rejoin nodes. 
     The performance data output by these tests is stored with the parameters that affected the creation of the prediction graph and any decisions made by the predictor component or local cache purging component. If the performance data are not acceptable in any way (do not meet any desired combination of weighted threshold tests) (block  1560 ), then the analyzer tool may adjust any of the parameters mentioned, regenerate the prediction graph if needed and re-run the above tests by returning to block  1505 . This automatic iterative process is directed at finding the best performing system (best performance data). As many of the parameters are extremely sensitive and have non-linear affects on system performance, various algorithms may be used to adjust the parameters for the next iteration. Such algorithms include heuristics (‘rules of thumb’) input by a human or learned automatically over time as having a good affect in previous analyzer sessions, Fuzzy Logic (a method utilizing the ‘fractional truth-hood’ of multiple ‘if-condition-then-action rules’ (each of which is somewhat similar to a heuristic); these rules all work (‘fire’) in parallel and the results are combined and then ‘defuzzified’ using various standard algorithms to produce a final precise decision of how to adjust the system to achieve a desired affect), Neural Networks, or any other relevant algorithms that allow complex non-linear functions to be modeled and adjusted. 
     It will be recognized that many other data structures and mechanisms may be used to preload resources associated with a resource hint list in the way described above. For example, the stack may include pointers to resource list objects. Each resource list object may keep track of which resource should be loaded next when the object is being used to preload resources. Using this mechanism, a hint may cause a new pointer to a resource object to be pushed on the stack. The newly pushed resource object may then be activated and used to begin preloading resources. When all the resources associated with the resource object have been preloaded, the stack may discard the pointer to the resource object and pop a pointer to the resource object used just previous to the hint being received. 
     It will be recognized that the above mechanisms of pushing resource lists (or pointers) allow multiple hints to be received and stored on a stack, with the most recent hint being used to preload resources. Another hint may be received while resources associated with a current hint are being preloaded. Receiving another hint may cause preloading of the resources associated with a current hint to be suspended until the resources associated with the other hint are preloaded. 
     In another embodiment of the invention, a reference from a resource list may be inserted anywhere in a preloader&#39;s list of resources to load. For example, a first-in-first-out queue, a priority queue, a linked list, or a graph could be used by a preloader to determine which resource should be loaded next. According to an embodiment of the invention, a queue is maintained for each priority level. For example, if there are three different priority levels then there are three queues. In this way, the highest priority queues may be checked before lower priority queues are checked. An application could specify that resources associated with a hint should be loaded after a preloader has loaded other resources. This could be done, for example, by inserting references to the resources of a resource list at a desired location in a preloader&#39;s linked list of resources to load. This might be done, for example, using a predictive search mechanism that tries to determine which resources should be loaded next. A priority level is associated with the hint. Based on the priority level of the hint, the resource is loaded into the appropriate queue. According to one embodiment of the invention, application hints include a default priority level. Alternatively, the application may assign the priority level. 
     Using Resource Lists to Preload Data 
       FIG. 7  illustrates using static and dynamic resource lists to preload data, in accordance with aspects of the invention. In one embodiment of the invention, a resource list identifies resources that may be needed by an executing or soon-to-be executing program (hereinafter both referred to as “the executing program”). Resources are referenced above in relation to creating a resource list from an executing program. 
     For example, in one embodiment, the resource list may include a list of dynamic link libraries (dll&#39;s), executables, data files, configuration files, and the like, that may be required by the executing program. 
     Referring now to  FIG. 7 , after a start block, the process flows to block  710 , where resource information is retrieved for the next resources to load from the resource list. Moving to block  720 , the resource is preloaded. Flowing to decision block  730 , a determination is made as to whether there are any more resources left to preload in the resource list. When there are resources left to preload, the process flows to block  710  to repeat the process. When there are not resources left to preload, the process flows to an end block and returns to processing other actions. 
       FIG. 8  illustrates an exemplary resource name mapping table, in accordance with aspects of the invention. According to one embodiment of the invention, each entry in a resource list includes three parameters that identify the resource. These parameters may include, for example, the file in which the resource is located, the offset within that file, and the length of the resource. In another embodiment of the invention, instead of or in addition to multiple parameters, the resource list contains a data value or key associated with a resource. For example, a resource list may include a “name” of a resource. This name may map to a sequence of bytes at a particular offset within a particular file by using a mapping table. For example, the name may map to a part of a subroutine, function, library, module, or component of an application. The mapping table may include a plurality of tuples including fields such as (resource name, file, offset, length). By specifying a resource name, the mapping table may be used to find a chunk of data from a file. The resource name may be used to find an appropriate tuple. Once a tuple has been located, the other values of the tuple may be used to access the resource. When an application is updated to a new version, the tuples in the mapping table may be updated based on the new location of data or instructions that may occur during recompilation. Using a mapping table in this manner enables a resource list to identify the same resources even after recompilation. While one exemplary way of specifying a resource has been explained, there are many different ways to specify or package the resources. For example, one other way to package content is to break it into fixed-sized pages. In that case, the items specified are the page number and/or number of pages. Any way of identifying the content acceptable. 
     In an embodiment of the invention, a thread reads a resource list, item-by-item, and preloads resources, as illustrated in  FIG. 7 . The thread may run in the background and/or may be given a selectable priority. Depending on the priority, the thread may consume a particular amount of computing resources such as processor compute cycles and network bandwidth. The thread may or may not execute when threads of higher priority are blocking and/or not executing. Control of the preloader may also be given to the application and/or the user. Accordingly, the preloader consumption of the CPU/memory and network resources may be controlled, rather than just relying on thread priority. 
     Preloader 
     When discussing using resource lists to preload data, a preloader may read a resource list, item-by-item, and preload the resources. In one embodiment of the invention, the preloader preloads resources from a resource list as soon as a user has logged onto the system. Even if the user logs off of the system, the preloader may keep preloading content while the user is doing (or not doing) other things, such as surfing the Internet, etc. 
     According to one embodiment, the preloader runs in the background. It may be configured to use a certain percentage of the available CPU cycles and/or bandwidth to the Internet, or any other resource like memory, operating system resources, and the like. The available bandwidth may vary as the user engages in different activities. For example, when a user is not utilizing the Internet, 100% of the Internet bandwidth may be available. A preloader configured to use 25% of the available bandwidth may during this time use 25% of the total bandwidth available to the Internet. At other times, the user may be surfing the Web. During these times, amount of bandwidth required by a user may vary. If, at a particular time, the user is using 50% of the total available bandwidth available from the computer to access the Internet, a preloader configured to use 25% of the available bandwidth would use 25% of the 50% remaining, i.e., 12.5% of the total available bandwidth. 
     Alternatively, a preloader may be configured to use a percentage of the total bandwidth available to the Internet. For example, the preloader may be configured to use 50% of the total bandwidth available to the Internet. While the preloader is actively preloading, the preloader will attempt to consume 50% of the total bandwidth available, regardless of what percentage of the bandwidth the user is currently using. 
     Preloading for an application may be enabled or disabled. Enabling and disabling may be done automatically or by a user. For example, at certain times a user may require all of the computational and bandwidth resources of their computing device. In a graphical user interface environment, the user may select an icon associated with the preloading and disable the preloading. Alternatively, or in addition, a user may set times in which the preloader may preload data and may also set how much computational and bandwidth resources the preloader may consume throughout a schedule. A schedule may assign the same computational and bandwidth resources for certain days, e.g. during working days one schedule may apply, and be different for other days, e.g., during weekends a different schedule may apply. A schedule for a preloader&#39;s consumption of computational and bandwidth resources may be intricate and detailed, simple, or of any type imaginable without departing from the spirit or scope of the invention. 
     In an embodiment of the invention, the user may enable preloading files for certain applications and/or priorities between the applications. For example, in adjusting priorities of preloading between applications, the user may assign a particular portion of the bandwidth available to a preloader to one application and another portion of the bandwidth available to the preloader to another application. Throughout this document, where it makes sense, bandwidth relates to both CPU compute cycles and the rate at which a client can send data to and receive data from a local area network or wide area network, such as the Internet. 
     In another embodiment of the invention, when the user assigns priorities between preloading resources for applications, the resources for the highest priority application are preloaded first. Then, the resources for the next highest priority application are preloaded, and so on. 
       FIG. 9  illustrates a state diagram of an in-app and out-of-app preloader executing. In one embodiment of the invention, one preloader is active before an application is launched, while another preloader is active after the application is launched. The preloaders may communicate through the use of a mutex or some other inter-process communications mechanism. The preloader that is active before an application is launched may be referred to as an out-of-app preloader (hereinafter referred to as either “out-of-app preloader” or “preloader”), while the preloader that is active when the application is executing may be referred to as an in-app preloader (hereinafter referred to “in-app preloader”). According to another embodiment, one preloader handles preloading for the application both while it is executing as well as when it is not executing when the presence of the application can be determined automatically. 
       FIG. 10  shows a process for in-app preloader execution, in accordance with aspects of the invention. The preloader may preload resources based on a static resource list that may be updated with resource lists associated with hints as described earlier. When the preloader determines that the application has launched, the preloader may suspend itself from executing. In doing so, the preloader may discard the resource (or chunk of a resource) which it was currently trying to load, finish loading the resource or chunk of data before suspension, or indicate how much of the resource or chunk it was able to preload before suspending. When the preloader resumes preloading resources, it may start with where it left off. 
     Some time after suspension, the preloader may be activated by the operating system or some other mechanism. Upon renewed execution, the preloader may check to see if the application is executing (block  1010 ). If it is, the preloader may suspend itself for another period of time (block  1020 ). This may continue until the preloader determines that the application is no longer executing (block  1030 ), for example, when a mutex is released. According to another embodiment of the invention, the preloading may be enabled and disabled in an event-driven manner. At this point, the preloader may resume preloading files where it left off. 
     When the preloader resumes preloading resources, it may determine that one or more resources that it was going to preload were loaded by the application or an in-app preloader (block  1060 ). The preloader may make this determination by checking a cache, memory, a file system I/O API, or some other location, to see if the file is already located local to the client. If so, the preloader may simply proceed to the next resource to load in the resource list (block  1050 ). The preloader may determine the next resource, too, was already preloaded by the application or an in-app preloader. As part of its procedure, the preloader may simply check to determine whether a resource in a resource list already exists locally. The term “locally” refers to the resource stored in a point that is more or less instantly accessible and of high bandwidth. For example, the resource may be stored in memory, hard drive, LAN server cache, proxy, and the like. The term locally is not restricted to residing only on the user&#39;s machine 
     If the resource does exist locally, the preloader may skip to the next resource and check to see if it already exists locally. This may continue until the preloader has stepped through all of the resources in a resource list (block  1040 ) or until the preloader finds a resource that needs to be preloaded. When the preloader finds a resource that needs to be preloaded, it may begin preloading the resource (block  1070 ). 
     These methods of preloading are directed at transferring resources from servers onto the user&#39;s local storage devices in order that the resources may be accessed much faster and with less chance of error than if they remained on the server. However, space on the user&#39;s local storage devices may be limited, and/or shared between multiple applications being preloaded. The user may also choose to ration the amount of local storage space that the content delivery system can use. Therefore there may be occasions when there is not enough space in the local storage area to hold all the resources that the preloader intends to load. If this occurs, any of a number of local-storage-space-management policies may be employed. Resources may be purged from the local storage system based on a “least recently used” algorithm or any other appropriate algorithm, in order to make room for new preloaded resources. As resources that have been recently used by the application are often likely to be requested again, such “least recently used” purging may also be limited to resources that meet certain other criteria, such as “not used for X hours”. When using the ‘prediction graph and predictor component’ algorithms described earlier, it may be advantageous to track which resources were preloaded due to these state-driven predictions, and when the application chooses a particular path forward through the prediction graph (i.e. makes a specific resource request), then mark any ‘failed predictions’ (resources that were predicted due to looking ahead down the branches in the graph that were not taken by the application), as being more suitable for purging if space needs to be reclaimed. 
       FIG. 11  illustrates a process flow of an in-app preloader, in accordance with aspects of the invention. The process illustrated in  FIG. 11  is substantially similar to the process illustrated in  FIG. 12  with the exception of blocks  1110  and  1120 . Upon execution of an application, the application indicates that it is executing (block  1110 ). The application may use a mutex, or utilize a call within an API to signal to a preloader that the application is now executing. Alternatively, or in addition, an in-app preloader may use a mutex (or some other inter-process communications mechanism) to signal to the out-of-app preloader that the in-app preloader is executing. Decision block  1120  is used to determine if the application is requesting resources. These resources may be requested directly from an application executing or through the use of hints or a predictor based on the application states. 
     In one embodiment of the invention, the in-app preloader uses a different resource list for preloading resources than the out-of-app preloader. An application, for example, may dynamically provide a resource list to an in-app preloader based on events that occur while the application is executing. Alternatively the same resource list may be used while the application is executing and when it is not executing. Furthermore, the application may have a set of resources that would be more beneficial to be preloaded than the set of resources that an out-of-app preloader would normally preload. When an in-app preloader begins preloading resources (based on a dynamic or static resource list), the in-app preloader may determine that the out-of-app preloader has already loaded one or more resources that the in-app preloader would have loaded. In such cases, the in-app preloader may skip to the next resource similar to how the out-of-app preloader skipped to the next resource when the out-of-app preloader determined that a file was already loaded. This skipping of files may be accomplished by the same mechanism. That is, both an out-of-app preloader and an in-app preloader may call a file system I/O API to load a particular resource. If the file system I/O API determines that the file is found locally, it may simply report to the calling preloader that the file has been loaded. Thus, in one embodiment of the invention, both out-of-app and in-app preloaders can be implemented that call a common API to load files. The file may be stored in a cache, a data store, or some combination of permanent and non-permanent memory. 
     In one embodiment of the invention, the preloader initially loads a minimum set of resources needed to start an application. This minimum set of resources may be referred to as a minimum footprint. Generally, such resources must be present on the client before an application executes. This minimum footprint might include a file system I/O API that enables the application to request other resources as needed. 
     Some sets of resources may require that an entire file be preloaded before any of the resources are accessed. Some examples include way files, mp3 files, and other files that need to be passed off to another system, such as a player or operating system external to the application. These resources may indicate that a set of such resources must be loaded together before any of the resources in the set are considered “available” to the application. 
     In one embodiment of the invention, resource lists may indicate that some resources should be pinned into memory, either on the hard drive, RAM, or some other storage. When a resource has an indication that it should remain in memory, it may cease to be subject to replacement under a least recently used (LRU) algorithm or some other resource replacement strategy. 
     Through the course of loading resources and minimum footprints, the user experiences the installation of an application. For example, icons associated with applications may be placed on the desktop of a windowing environment. Icons may also be placed in the Microsoft Windows® “Start Menu”. The user has the same experience as any typical installation of an application even though the entire application is not loaded onto the user&#39;s machine. 
     A preloader, however, may or may not wait until such icons are accessed or clicked upon before beginning to preload resources associated with the application which the icons represent. Accessing one icon may cause a preloader to begin preloading a resource for an application not directly related to that icon. For example, the preloader may determine that if a user accesses one application that the user has a high probability of accessing another application. In these cases, upon selection of an icon, resources for a set of applications may begin to be preloaded. 
     In some cases, an application may need a resource that a preloader has not preloaded. In one embodiment of the invention, when the application needs such a resource, it may request the resource from memory, cache, file system I/O API, and the like. When an in-app preloader detects that the application has requested a resource, the in-app preloader may suspend itself and remain suspended until the application&#39;s resource request is fulfilled. To determine when the application has received its requested resource, the in-app preloader may enter a loop in which it sleeps, awakes and checks the status of the application request, and sleeps again if the resource has not yet been transferred to a local storage device. 
     In some embodiments of the invention, resources may be requested in 32 kilobyte and/or 64 kilobyte chunks. The chunk size may be selected manually or automatically and may be set to a size other than 32 or 64 kilobytes. 
     In another embodiment of the invention, a client may have multiple channels of communication with a content server. For example, an in-app preloader may send requests and receive data on one channel, an out-of-app preloader may send requests and receive data on another channel, and an application may send requests and receive data on yet another channel. A server may receive a request on one channel and then receive a request on another channel from the same client. If the new request is from a channel of a higher priority, the server may stop fulfilling the request from any lower channel until the higher priority channel&#39;s request is satisfied. In such embodiments, it may be unnecessary for the client&#39;s out-of-app preloader to check whether an in-app preloader or application is executing because by setting priorities, the server may be configured to transfer data to the out-of-app preloader when the server was not servicing a request from the in-app preloader or the application. Likewise, it may be unnecessary for the in-app preloader to check whether the application is requesting data. By setting priorities, a server may be configured to send data to the in-app preloader when the server is not servicing a request from the application. 
     According to another embodiment, a single preloader is used for in-app preloading and out-of-app preloading. Instead of individual preloaders for each application, an engine manages preloading. During in-app preloading the application may send requests using an API call to the preloader. For example, a player is nearing the next level in the game, and the application requests the resources needed for the next level from the preloader. During out-of-app preloading the preloader may load resources from a resource list. In other words, the resource list is static when the application is not executing, and is a dynamic resource list when the application is executing. When the application begins executing it registers with the preloader that it is executing. This embodiment has many advantages. For example, the application consumes less resources on the client since it doesn&#39;t store a copy of the preloader. Additionally, there is a central point from which to control preloading of resources. 
       FIG. 12  shows a preloader system, in accordance with aspects of the invention. Client  1205  may include connection manager  1210  and one or more applications, such as applications  1215 - 1217 . Each application may be associated with one or more caches, such as caches  1220 - 1222 . In another embodiment of the invention, all of the applications are associated with a single cache. That is, a single cache may store content for more than one application. The caches may be stored on a computer-readable medium located on client  1205  or easily accessible by client  1205 , such as on a server coupled by a LAN to client  1205 . 
     Content may be divided into one or more resources. When a client computer first requests an application, such as a game, the resources of the game may be located solely on a content server. The executable code and data that comprises the application may both be divided into blocks. Each of these blocks could be considered a resource needed by the application to continue or complete execution. 
     Some of the blocks of executable code of the application may be downloaded from the server and stored on the client computer. After a sufficient number of blocks are downloaded, the application may start executing with the blocks that are currently available on the client computer. Before or when the application comes to a part in the code in which it needs code located on the content server, the application may request a block of code containing the needed code. This block of code would be a resource needed by the application to continue or complete execution. 
     A resource may be identified by information including the name of the file together with an offset in the file and bytes requested. The file may be a data file, a dynamic link library, an executable program, a component, and the like. Resources may also include such things as a processor, memory, a printer, a display adapter, a network adapter, a storage device such as a hard disk, CD-ROM, DVD disk, or other optical disk, and the like, although it will be recognized that these devices would not be downloaded from a content server to a client computer. 
     Client  1210  is coupled by a WAN/LAN (not shown) to one or more servers, such as servers  1225 - 1227 . 
     In one embodiment of the invention, each application is associated with a preloader thread. For example, application  1215  may be associated with preloader thread  1230 . Preloader thread  1230  is in charge of obtaining content that application  1215  currently needs or will shortly need. Preloader thread  1230  may know which content application  1215  will shortly need by examining a static resource list previously generated. For example, application  1215  may be instrumented to output a list of which resources it accesses during a sample execution. Application  1215  may be executed several times under varying circumstances to obtain a representative or constructed list of resources typically needed by application  1215 . 
     When application  1215  is using resources that are currently available on client  1215 , preloader thread  1230  may request resources from the static resource list to be retrieved from a content server. As requested resources are received, they may be stored in a cache associated with application  1215 , such as cache  1220 . Then, when application  1215  requires the resource, it may be retrieved from a computer storage medium locally accessible rather than a content server. 
     When application  1215  requires a resource that is not locally accessible on client  12415 , application  1215  may utilize preloader thread  1230  or may directly request the resource from engine  1235 . After the resource is retrieved, it may then be stored in a cache associated with application  1215 . In addition, the resource may then be provided to application  1215  for use. 
     In another embodiment of the invention, each application ( 1215 - 1217 ) receives preloaded resources directly from engine  1235 . According to this embodiment, an application informs engine  1235  of its current status. In response to the status, engine  1235  requests any resources that are needed by the application. These resources may be sent to the application or may be stored in a cache. Engine  1235  may manage a thread pool ( 1238 ) that contains threads relating to the resources to be preloaded that are associated with the applications. 
     Connection manager  1210  may be used to manage the retrieval of resources from one or more content servers. For example, connection manager  1210  may receive requests for resources from one or more applications, such as applications  1215 - 1217 , or preloader threads, such as preloader threads  1230 - 1232 . Connection manager  1210  may also operate on user configuration data. For example, a user may configure connection manager  1210  to use no more than a particular percentage of available bandwidth the computer has to the Internet. 
     When an application becomes active and actively requests resources, connection manager  1210  may suspend preloading resources for non-active applications and devote all available bandwidth that has been allotted by a user to connection manager  1210  to retrieve resources for the active application. The application may also request resources and place them in a cache associated with the application. 
     In one embodiment of the invention, connection manager  1210  is integrated with an application. That is, when only one application is executing, it may not be necessary to have connection manager  1210  managing connections from multiple applications. Rather, its functionality may be included in an application. 
     Connection manager  1210  may have one or more connections to content servers  1225 - 1227 . In some embodiments of the invention, a single content server, such as content server  1226 , has sufficient bandwidth to service the needs of multiple clients. In other embodiments of the invention, multiple content servers may be required to service the needs of one or more clients. A connection manager that determines that it needs the bandwidth of more than one content server may open connections to more than one content server to obtain content. 
     Connection manager  1210  may have more than one connection to one content server. For example, connection manager  1210  may request content for more than one application at a time. The content may all reside on one content server, such as content server  1226 . Connection manager  1210  may open one connection for content for each application. 
     More preferably, however, connection manager  1210  maintains only one connection with each content server which has content connection manager  1210  is requesting. Despite some added complexity in multiplexing content through one connection, this has added benefits in minimizing the number of connections to a content server. If every connection manager from every client were to open multiple connections to each content server, these limited connections might be rapidly consumed. 
     In addition, connection manager  1210  may close a connection when the connection is not being used. This may also help the connection capacity of content servers. 
     Illustrative Operating Environment 
       FIGS. 1-3  show components of an exemplary environment in which the invention may be practiced. Not all of the components may be required to practice the invention, and variations in the arrangement and type of the components may be made without departing from the spirit or scope of the invention. 
       FIG. 1  shows a plurality of local area networks (“LANs”)  120  and wide area network (“WAN”)  130  interconnected by routers  110 . Routers  110  are intermediary devices on a communications network that expedite message delivery. On a single network linking many computers through a mesh of possible connections, a router receives transmitted messages and forwards them to their correct destinations over available routes. On an interconnected set of LANs—including those based on differing architectures and protocols—, a router acts as a link between LANs, enabling messages to be sent from one to another. Communication links within LANs typically include twisted pair, fiber optics, or coaxial cable, while communication links between networks may utilize analog telephone lines, full or fractional dedicated digital lines including T1, T2, T3, and T4, Integrated Services Digital Networks (ISDNs), Digital Subscriber Lines (DSLs wireless links, or other communications links known. Furthermore, computers, such as remote computer  140 , and other related electronic devices can be remotely connected to either LANs  120  or WAN  130  via a modem and temporary telephone link. The number of WANs, LANs, and routers in  FIG. 1  may be increased or decreased arbitrarily without departing from the spirit or scope of this invention. 
     As such, it will be appreciated that the Internet itself may be formed from a vast number of such interconnected networks, computers, and routers. Generally, the term “Internet” refers to the worldwide collection of networks, gateways, routers, and computers that use the Transmission Control Protocol/Internet Protocol (“TCP/IP”) suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, including thousands of commercial, government, educational, and other computer systems, that route data and messages. An embodiment of the invention may be practiced over the Internet without departing from the spirit or scope of the invention. 
     The media used to transmit information in communication links as described above illustrates one type of computer-readable media, namely communication media. Generally, computer-readable media includes any media that can be accessed by a computing device. Computer-readable media may include computer storage media, communication media, or any combination thereof. 
     Communication media typically embodies 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 includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, communication media includes wired media such as twisted pair, coaxial cable, fiber optics, wave guides, and other wired media and wireless media such as acoustic, RF, infrared, and other wireless media. 
     The Internet has recently seen explosive growth by virtue of its ability to link computers located throughout the world. As the Internet has grown, so has the World Wide Web (WWW). Generally, the WWW is the total set of interlinked hypertext documents residing on HTTP (hypertext transport protocol) servers around the world. Documents on the WWW, called pages or Web pages, are typically written in HTML (Hypertext Markup Language) or some other markup language, identified by URLs (Uniform Resource Locators) that specify the particular machine and pathname by which a file can be accessed, and transmitted from server to end user using HTTP. Codes, called tags, embedded in an HTML document associate particular words and images in the document with URLs so that a user can access another file, which may literally be halfway around the world, at the press of a key or the click of a mouse. These files may contain text (in a variety of fonts and styles), graphics images, movie files, media clips, and sounds as well as Java applets, ActiveX controls, or other embedded software programs that execute when the user activates them. A user visiting a Web page also may be able to download files from an FTP site and send messages to other users via email by using links on the Web page. 
     A server, such as the server shown in  FIG. 2 , may provide a WWW site, be a content server, a game server, an authentication server, etc. When providing Web pages, the server may have storage facilities for storing hypertext documents for a WWW site and running administrative software for handling requests for the stored hypertext documents. A hypertext document normally includes a number of hyperlinks, i.e., highlighted portions of text which link the document to another hypertext document possibly stored at a WWW site elsewhere on the Internet. Each hyperlink is associated with a URL that provides the location of the linked document on a server connected to the Internet and describes the document. Thus, whenever a hypertext document is retrieved from any WWW server, the document is considered to be retrieved from the WWW. A WWW server may also include facilities for storing and transmitting application programs, such as application programs written in the JAVA programming language from Sun Microsystems, for execution on a remote computer. Likewise, a WWW server may also include facilities for executing scripts and other application programs on the WWW server itself. 
     A user may retrieve hypertext documents from the WWW via a WWW browser application program located on a wired or wireless device. A WWW browser, such as Netscape&#39;s NAVIGATOR® or Microsoft&#39;s INTERNET EXPLORER®, is a software application program for providing a graphical user interface to the WWW. Upon request from the user via the WWW browser, the WWW browser accesses and retrieves the desired hypertext document from the appropriate WWW server using the URL for the document and HTTP. HTTP is a higher-level protocol than TCP/IP and is designed specifically for the requirements of the WWW. HTTP is used to carry requests from a browser to a Web server and to transport pages from Web servers back to the requesting browser or client. The WWW browser may also retrieve application programs from the WWW server, such as JAVA applets, for execution on a client computer. 
       FIG. 2  shows an exemplary server that may operate to provide a WWW site, other content, and/or services, among other things. When providing a WWW site, server  200  transmits WWW pages to the WWW browser application program executing on requesting devices to carry out this process. For instance, server  200  may transmit pages and forms for receiving information about a user, such as address, telephone number, billing information, credit card number, etc. Moreover, server  200  may transmit WWW pages to a requesting device that allow a consumer to participate in a WWW site. The transactions may take place over the Internet, WAN/LAN  100 , or some other communications network. 
     Server  200  may include many more components than those shown in  FIG. 2 . However, the components shown are sufficient to disclose an illustrative environment for practicing the present invention. As shown in  FIG. 2 , server  200  is connected to WAN/LAN  100 , or other communications network, via network interface unit  210 . The network interface unit  210  includes the necessary circuitry for connecting server  200  to WAN/LAN  100 , and is constructed for use with various communication protocols including the TCP/IP protocol. Typically, network interface unit  210  is a card contained within server  200 . 
     Server  200  also includes processing unit  212 , video display adapter  214 , and a mass memory, all connected via bus  222 . The mass memory generally includes random access memory (“RAM”)  216 , read-only memory (“ROM”)  232 , and one or more permanent mass storage devices, such as hard disk drive  228 , a tape drive (not shown), optical drive  226 , such as a CD-ROM/DVD-ROM drive, and/or a floppy disk drive (not shown). The mass memory stores operating system  220  for controlling the operation of server  200 . It will be appreciated that this component may comprise a general purpose server operating system, such as UNIX, LINUXT™, or Microsoft WINDOWS NT®. Basic input/output system (“BIOS”)  218  is also provided for controlling the low-level operation of server  200 . 
     The mass memory as described above illustrates another type of computer-readable media, namely computer storage media. Computer storage media may 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. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by a computing device. 
     The mass memory may also store program code and data for providing a WWW site. More specifically, the mass memory may store applications including WWW server application program  230 , and programs  234 . WWW server application program  230  includes computer executable instructions which, when executed by server  200 , generate WWW browser displays, including performing the logic described above. Server  200  may include a JAVA virtual machine, an SMTP handler application for transmitting and receiving email, an HTTP handler application for receiving and handing HTTP requests, JAVA applets for transmission to WWW browser executing on a client computer, and an HTTPS handler application for handling secure connections. The HTTPS handler application may be used for communication with an external security application to send and receive sensitive information, such as credit card information, in a secure fashion. 
     Server  200  also comprises input/output interface  224  for communicating with devices, such as a mouse, keyboard, scanner, or other input devices not shown in  FIG. 2 . Likewise, server  200  may further comprise additional mass storage facilities such as optical drive  226  and hard disk drive  228 . Hard disk drive  228  is utilized by server  200  to store, among other things, application programs, databases, and program data used by WWW server application program  230 . For example, customer databases, product databases, image databases, and relational databases may be stored. 
       FIG. 3  depicts several components of client computer  300 . Client computer  300  may include many more components than those shown in  FIG. 3 . However, it is not necessary that those conventional components be shown in order to disclose an illustrative embodiment for practicing the present invention. As shown in  FIG. 3 , client computer  300  includes network interface unit  302  for connecting to a LAN or WAN, or for connecting remotely to a LAN or WAN. Network interface unit  302  includes the necessary circuitry for such a connection, and is also constructed for use with various communication protocols including the TCP/IP protocol, the particular network configuration of the LAN or WAN it is connecting to, and a particular type of coupling medium. Network interface unit  302  may also be capable of connecting to the Internet through a point-to-point protocol (“PPP”) connection or a serial line Internet protocol (“SLIP”) connection. 
     Client computer  300  also includes BIOS  326 , processing unit  306 , video display adapter  308 , and memory. The memory generally includes RAM  310 , ROM  304 , and a permanent mass storage device, such as a disk drive. The memory stores operating system  312  and programs  334  for controlling the operation of client computer  300 . The memory also includes WWW browser  314 , such as Netscape&#39;s NAVIGATOR® or Microsoft&#39;s INTERNET EXPLORER® browsers, for accessing the WWW. It will be appreciated that these components may be stored on a computer-readable medium and Loaded into memory of client computer  300  using a drive mechanism associated with the computer-readable medium, such as a floppy disk drive (not shown), optical drive  316 , such as a CD-ROM/DVD-ROM drive, and/or hard disk drive  318 . Input/output interface  320  may also be provided for receiving input from a mouse, keyboard, or other input device. The memory, network interface unit  302 , video display adapter  308 , and input/output interface  320  are all connected to processing unit  306  via bus  322 . Other peripherals may also be connected to processing unit  306  in a similar manner. 
     As will be recognized from the discussion below, aspects of the invention may be embodied on server  200 , on client computer  300 , or on some combination thereof. For example, programming steps may be contained in programs  334  and/or programs  234 . 
     In this disclosure, references will be made to client and server. Where appropriate, client should be construed to refer to a process or set of processes that execute on one or more electronic device, such as client computer  300  of  FIG. 3 . A client is not limited, however, to running on a client computer. It may also run on a server, such as WWW server  200  or be distributed among various electronic devices, wherein each device might contain one or more processes or routines that together constitute a client application. Where appropriate, client should be construed, in addition or in lieu of the discussion above, to be a device upon which one or more client processes execute, for example, client computer  300  or WWW server  200 . 
     Similarly, server should be construed to refer to a process or set of processes that execute on one or more electronic devices, such as WWW server  200 . Like a client, a server is not limited to running on a server computer. Rather, it may also execute on what would typically be considered a client computer, such as client computer  300  of  FIG. 3 , or be distributed among various electronic devices, wherein each device might contain one or more processes or routines that together constitute a server application. Where appropriate, server should be construed, in addition or in lieu of the discussion above, to be a device upon which one or more server processes execute, for example, server  200  or client computer  300 . 
     Encryption and Decryption 
     Throughout this disclosure, references to encryption and decryption are made. Where appropriate, each reference to an algorithm used to perform encryption or decryption should be construed to include any other algorithm or technique for making it more difficult to obtain the original bytes (also called plaintext) of an application, component of an application, and/or data. For each reference to an algorithm used to perform encryption or decryption throughout this disclosure, it should also be recognized that other embodiments of the invention may be implemented using other encryption algorithms, including the proposed Advanced Encryption Standard (AES) which is Rjindael, RSA Labs Inc.&#39;s (hereinafter “RSA&#39;s”) RC6, IBM&#39;s MARS, TwoFish, Serpent, CAST-256, International Data Encryption Algorithm (IDEA), Data Encryption Standard (DES), Triple DES, DES-EDE2, DES-EDE3, DESX, DES-XEX3, RC2, RC5, Blowfish, Diamon2, TEA, SAFER, 3-WAY, GOST, SHARK, CAST-128, Square, Skipjack, Panama, ARC4, SEAL, WAKE, Sapphire II, BlumBlumShub, RSA, DSA, ElGamal, Nyberg-Rueppel (NR), BlumGoldwasser, Rabin, Rabin-Williams (RW), LUC, LUCELG, ECDSA, ECNR, ECIES, ECDHC, ECMQVC, and/or any other encryption algorithm. These encryption algorithms may use, where appropriate, cipher block chaining mode, cipher feedback mode, CBC ciphertext stealing (CTS), CFB, OFB, counter mode, and/or any other block mode. Other exemplary “encryption” techniques that may be used by embodiments of the invention include compiling source code into binary code, and/or using proprietary data structures to send data. In one embodiment of the invention, Crypto++ v4.x, an open-source class library of cryptographic techniques, the source code of which is hereby incorporated by reference, may be used in encrypting or decrypting applications and/or data. Other encryption and decryption libraries, both open source, commercial, and/or proprietary may be used without departing from the spirit or scope of the invention. 
     In one embodiment of the invention, for symmetric encryption and decryption 128-bit keys and the proposed-AES Rjindael cipher may be used in cipher block chaining mode. Random initialization vectors (IVs) may be sent in plaintext. In another embodiment to protect a password stored on a client, 256-bit Rjindael in cipher feedback mode is used with a random IV. In other embodiments of the invention, other symmetric encryption algorithms (such as the ones listed in the previous paragraph) may be used for symmetric encryption and decryption. 
     In one embodiment of the invention, for asymmetric encryption, 1024-bit keys may be used with RSA. These keys may be formatted according to the “OAEP (with SHA1)” scheme provided by RSA, or any other formatting appropriate. For example, RSA may be used in conjunction with a ticket (which is described in more detail below) to decrypt data in the ticket to recover an AES key that may then be used to decrypt other portions of a ticket. SHA1 stands for secure hash algorithm 1. SHA1 is a cryptographic hash algorithm that produces a 160-bit hash value from an arbitrary length string. In other embodiments of the invention other private key/public key encryption algorithms may be used (such as the ones listed above) with the same or different key sizes. 
     In another embodiment of the invention, a server and/or client may also employ a 128-bit HMAC (hashed message authentication code) and/or 1024-bit RSA digital signatures to assist in authenticating that the contents of a ticket have not been changed and/or in authenticating a client and/or server. The 128-bit HMAC may use SHA1 to create a digest of data. For example, contents of a ticket may be fed into a one way hashing function, such as SHA1, to create a block of binary digits. The hashing function may be such that whatever is inputted into it is hashed into fixed length of bits. For example, the hashing function may return 160 bits whether it operates on 4 bytes of data or on all the text in the Bible. A RSA signature may be created and/or formatted as described in RSA&#39;s PKCS #1 v2.0, or any other suitable format. 
     Encryption may be used to protect tickets in a somewhat similar fashion to the Kerberos open protocol from the Massachusetts Institute of Technology (MIT), which is hereby incorporated by reference. Embodiments of the invention that may be used to protect tickets and authenticate clients and/or servers are described below. 
     Keys may be distributed using 1024-bit RSA and a 128-bit Rjindael symmetric session key. The 1024-bit RSA key may be used to encrypt the 128-bit Rjindael symmetric key. The 128-bit Rjindael key may be used to encrypt the body of a message. To recover a message body, a receiver may use its private RSA key to obtain the 128-bit Rjindael key. Then the 1.28-bit Rjindael key may be used to decrypt the body of the message. Tickets may include other encrypted 128-bit Rjindael session keys that are sent from one server to another server in a somewhat similar manner to that described in the open Kerberos protocol from MIT. 
     Encrypted or unencrypted messages or tickets may be sent using TCP/IP, UDP, SSL, IPSEC, or any other networking protocol. Content sent to or from content servers may be encrypted on unencrypted. Random numbers may be generated by any random number generator. An exemplary random number generator that may be used is CryptoAPI, produced by Microsoft Corporation of Redmond, Wash. 
     It will be recognized that the key sizes given above are illustrative. In other embodiments of the invention, key sizes other than or in addition to the key sizes above may be used when encrypting data and/or authenticating a server, client, or user. 
     The various embodiments of the invention may be implemented as a sequence of computer implemented steps or program modules running on a computing system and/or as interconnected machine logic circuits or circuit modules within the computing system. The implementation is a matter of choice dependent on the performance requirements of the computing system implementing the invention. In light of this disclosure, it will be recognized by one skilled in the art that the functions and operation of the various embodiments disclosed may be implemented in software, in firmware, in special purpose digital logic, or any combination thereof without deviating from the spirit or scope of the present invention. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.