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70-633: ALSP consists of: In 1990, the Defense Advanced Research Projects Agency (DARPA) employed The MITRE Corporation to study the application of distributed interactive simulation principles employed in SIMNET to aggregate-level constructive training simulations. Based on prototype efforts, a community-based experiment was conducted in 1991 to extend SIMNET to link the US Army's Corps Battle Simulation (CBS) and

140-446: A confederation of simulations that coordinate using a common model. To design a mechanism that permits existing simulations to interact, two strategies are possible: (1) define an infrastructure that translates between the representations in each simulation, or (2) define a common representational scheme and require all simulations to map to that scheme. The first strategy requires few perturbations to existing simulations; interaction

210-418: A confederation, but many simulations require knowledge of some objects. A simulation uses simulation protocol update messages to discover objects owned by other simulations. If this simulation is interested in the objects, it can ghost them (track their locations and state) and model interactions to them from owned objects. Locks implement attribute ownership. A primary function of the object management protocol

280-570: A cooperation among Bell Labs , General Electric and MIT , which DARPA supported by funding Project MAC at MIT with an initial two-million-dollar grant. DARPA supported the evolution of the ARPANET (the first wide-area packet switching network), Packet Radio Network, Packet Satellite Network and ultimately, the Internet and research in the artificial intelligence fields of speech recognition and signal processing, including parts of Shakey

350-411: A deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process. If a process remains indefinitely unable to change its state because resources requested by it are being used by another process that itself is waiting, then the system is said to be in

420-408: A deadlock on single-instance resource systems, they only indicate the possibility of deadlock on systems having multiple instances of resources. Most current operating systems cannot prevent deadlocks. When a deadlock occurs, different operating systems respond to them in different non-standard manners. Most approaches work by preventing one of the four Coffman conditions from occurring, especially

490-508: A deadlock. In a communications system , deadlocks occur mainly due to loss or corruption of signals rather than contention for resources. A deadlock situation on a resource can arise only if all of the following conditions occur simultaneously in a system: These four conditions are known as the Coffman conditions from their first description in a 1971 article by Edward G. Coffman, Jr. While these conditions are sufficient to produce

560-436: A local area network). It also permits configurations where sets of ACMs communicate with their own local ABE with inter-ABE communication over wide area networks. The ALSP communication scheme consists of (1) an inter-component communications model that defines the transport layer interface that connects ALSP components, (2) a layered protocol for simulation-to-simulation communication, object management, and time management, (3)

630-599: A message filtering scheme to define the information of interest to a simulation, and (4) a mechanism for intelligent message distribution. AIS employs a persistent connection communications model to provide the inter-component communications. The transport layer interface used to provide inter-component communications was dictated by simulation requirements and the transport layer interfaces on AIS-supporting operating systems: local VMS platforms used shared mailboxes; non-local VMS platforms used either Transparent DECnet or TCP/IP; and UNIX-like platforms use TCP/IP. The ALSP protocol

700-482: A military exercise for the first time; this was well received. But the software application of DSI, distribution of Ground Warfare Simulation (GRWSIM), was less successful. The GRWSIM simulation was unreliable and its distributed database was inconsistent, degrading the effectiveness of the exercise. DARPA was funding development of a distributed tank trainer system called SIMNET where individual, computerized, tank-crew trainers were connected over local area networks and

770-666: A number of new technologies that were developed within the framework of the GXV-T program. The goal of this program is to create a lightly armored combat vehicle of not very large dimensions, which, due to maneuverability and other tricks, can successfully resist modern anti-tank weapon systems. In September 2020, DARPA and the US Air Force announced that the Hypersonic Air-breathing Weapon Concept (HAWC) are ready for free-flight tests within

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840-451: A simulation joins a confederation, all other ACMs in the confederation create input message queues for the new simulation. Conversely, when a simulation departs a confederation the other ACMs delete input message queues for that simulation. ALSP time management facilities support discrete event simulation using either asynchronous (next-event) or synchronous (time-stepped) time advance mechanisms. The mechanism to support next-event simulations

910-425: A simulation must be altered to participate in an ALSP confederation. The remaining modifications are: In stand-alone simulations, objects come into (and go out of) existence with the passage of simulation time and the disposition of these objects is solely the purview of the simulation. When acting within a confederation, the simulation-object relationship is more complicated. The simulation-object ownership property

980-611: A simulation takes an action between one of its objects and a ghost, the simulation must report this to the confederation. In the parlance of ALSP, this is an interaction. These fundamental concepts provide the basis for the remainder of the presentation. The term confederation model describes the object hierarchy, attributes and interactions supported by a confederation. The object-based conceptual framework adopted by ALSP defines classes of information that must be distributed. The ALSP Infrastructure Software (AIS) provides data distribution and process coordination. Principal components of AIS are

1050-415: A system. The term "deadlock avoidance" appears to be very close to "deadlock prevention" in a linguistic context, but they are very much different in the context of deadlock handling. Deadlock avoidance does not impose any conditions as seen in prevention but, here each resource request is carefully analyzed to see whether it could be safely fulfilled without causing deadlock. Deadlock avoidance requires that

1120-562: A whole series of X planes over the next 10 years. Between 2014 and 2016, DARPA shepherded the first machine-to-machine computer security competition, the Cyber Grand Challenge (CGC), bringing a group of top-notch computer security experts to search for security vulnerabilities , exploit them, and create fixes that patch those vulnerabilities in a fully automated fashion. It is one of DARPA prize competitions to spur innovations. In June 2018, DARPA leaders demonstrated

1190-407: Is The mechanism to support time-stepped simulation is: AIS includes a deadlock avoidance mechanism using null messages. The mechanism requires that the processes have exploitable lookahead characteristics. The ACM administers attribute database and filter information. The attribute database maintains objects known to the simulation, either owned or ghosted, and attributes of those objects that

1260-469: Is Stefanie Tompkins . As of 2021 , their mission statement is "to make pivotal investments in breakthrough technologies for national security". The Advanced Research Projects Agency (ARPA) was suggested by the President's Scientific Advisory Committee to President Dwight D. Eisenhower in a meeting called after the launch of Sputnik. ARPA was formally authorized by President Eisenhower in 1958 for

1330-406: Is a peer-level protocol that sits below the simulation protocol and provides object management services. ACMs solely use it for object attribute creation, acquisition, release, and verification (of the consistency of the distributed object database). These services allow AIS to manage distributed object ownership. Distributed object ownership presumes that no single simulation must own all objects in

1400-521: Is also a peer-level protocol that sits below the simulation protocol. It provides time management services for synchronizing simulation time among ACMs. The protocol provides services for the distributed coordination of a simulation's entrance into the confederation, time progression, and confederation saves. The join/resign services and time synchronization mechanisms are described in Section earlier. The save mechanism provides fault tolerance. Coordination

1470-466: Is an organizing structure of concepts that facilitates simulation model development. Common conceptual frameworks include: event scheduling, activity scanning and process interaction. The ALSP conceptual framework is object-based where a model is composed of objects that are characterized by attributes to which values are assigned. Object classes are organized hierarchically in much the same manner as with object-oriented programming languages. ALSP supports

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1540-525: Is based on a set of orthogonal issues that comprise ALSP's problem space: simulation-to-simulation communication, object management, and time management. These issues are addressed by a layered protocol that has at the top a simulation protocol with underlying simulation/ACM, object management, time management, and event distribution protocols. The simulation protocol is the main level of the ALSP protocol. It consists of four message types: The simulation protocol

1610-409: Is being used. Distributed deadlocks can be detected either by constructing a global wait-for graph from local wait-for graphs at a deadlock detector or by a distributed algorithm like edge chasing. Phantom deadlocks are deadlocks that are falsely detected in a distributed system due to system internal delays but do not actually exist. For example, if a process releases a resource R1 and issues

1680-586: Is credited with boosting the development of the fledgling personal computer industry. Some young computer scientists left the universities to startups and private research laboratories such as Xerox PARC . Between 1976 and 1981, DARPA's major projects were dominated by air, land, sea, and space technology, tactical armor and anti-armor programs, infrared sensing for space-based surveillance, high-energy laser technology for space-based missile defense, antisubmarine warfare, advanced cruise missiles, advanced aircraft, and defense applications of advanced computing. Many of

1750-405: Is dynamic, i.e. during its lifetime an object may be owned by more than one simulation. In fact, for any value of simulation time, several simulations may own different attributes of a given object. By convention, a simulation owns an object if it owns the "identifying" attribute of the object. Owning an object's attribute means that a simulation is responsible for calculating and reporting changes to

1820-443: Is easily possible since the resources that each process has locked and/or currently requested are known to the resource scheduler of the operating system. After a deadlock is detected, it can be corrected by using one of the following methods: Deadlock prevention works by preventing one of the four Coffman conditions from occurring. Similar to deadlock prevention, deadlock avoidance approach ensures that deadlock will not occur in

1890-401: Is facilitated entirely through the interconnection infrastructure. However, this solution does not scale well. Because of an underlying requirement for scalability, the ALSP design adopted the second strategy. ALSP prescribes that each simulation maps between the representational scheme of the confederation and its own representational scheme. This mapping represents one of the three ways in which

1960-527: Is required to produce a consistent snapshot of all ACMs, translators and simulations for a particular value of simulation time. The ACM uses simulation message filtering to evaluates the content of a message received from the confederation. The ACM delivers messages to its simulation that are of interest, and pass filtering criteria and discards those that are not of interest. The ACM filters two types of messages: update messages and interaction messages. Update messages. The ACM evaluates update messages based on

2030-490: Is text-based. It is defined by an LALR ( 1) context-free grammar. The semantics of the protocol are confederation-dependent, where the set of classes, class attributes, interactions, and interaction parameters are variable. Therefore, the syntactical representation of the simulation protocol may be defined without a priori knowledge of the semantics of the objects and interactions of any particular confederation. The simulation/ACM connection protocol provides services for managing

2100-474: Is the RTIC framework. Under the deadlock detection, deadlocks are allowed to occur. Then the state of the system is examined to detect that a deadlock has occurred and subsequently it is corrected. An algorithm is employed that tracks resource allocation and process states, it rolls back and restarts one or more of the processes in order to remove the detected deadlock. Detecting a deadlock that has already occurred

2170-498: Is to ensure that a simulation only updates attributes for which it has acquired a lock. The object manager in the ACM manages the objects and object attributes of the owned and ghosted objects known to the ACM. Services provided by the simulation/ACM protocol are used by the simulations to interact with the ACM's attribute locking mechanism. The coordination of status, request, acquisition, and release of object attributes, between ACMs, uses

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2240-579: The Advanced Research Projects Agency ( ARPA ), the agency was created on February 7, 1958, by President Dwight D. Eisenhower in response to the Soviet launching of Sputnik 1 in 1957. By collaborating with academia, industry, and government partners, DARPA formulates and executes research and development projects to expand the frontiers of technology and science, often beyond immediate U.S. military requirements. The name of

2310-597: The National Aeronautics and Space Administration ( NASA ) and the military space programs to the individual services. This allowed ARPA to concentrate its efforts on the Project Defender (defense against ballistic missiles), Project Vela (nuclear test detection), and Project AGILE ( counterinsurgency R&D) programs, and to begin work on computer processing, behavioral sciences , and materials sciences. The DEFENDER and AGILE programs formed

2380-644: The internet on the list of innovations for which DARPA can claim at least partial credit." Its track record of success has inspired governments around the world to launch similar research and development agencies. DARPA is independent of other military research and development and reports directly to senior Department of Defense management. DARPA comprises approximately 220 government employees in six technical offices, including nearly 100 program managers, who together oversee about 250 research and development programs. The agency's current director, appointed in March 2021,

2450-574: The ALSP Common Module (ACM) and the ALSP Broadcast Emulator (ABE). The ALSP Common Module (ACM) provides a common interface for all simulations and contains the essential functionality for ALSP. One ACM instance exists for each simulation in a confederation. ACM services require time management and object management; they include: Joining and departing a confederation is an integral part of time management process. When

2520-623: The Adaptive Suspension Vehicle (ASV) nicknamed the "Walker" at the Ohio State University , under a research contract from DARPA. The vehicle was 17 feet long, 8 feet wide, and 10.5 feet high, and had six legs to support its three-ton aluminum body, in which it was designed to carry cargo over difficult terrains. However, DARPA lost interest in the ASV, after problems with cold-weather tests. On February 4, 2004,

2590-818: The Agency was centered on information processing and aircraft-related programs, including the National Aerospace Plane (NASP) or Hypersonic Research Program. The Strategic Computing Program enabled DARPA to exploit advanced processing and networking technologies and to rebuild and strengthen relationships with universities after the Vietnam War . In addition, DARPA began to pursue new concepts for small, lightweight satellites ( LIGHTSAT ) and directed new programs regarding defense manufacturing, submarine technology, and armor/anti-armor. In 1981, two engineers, Robert McGhee and Kenneth Waldron, started to develop

2660-738: The DSI to cooperate in a single, virtual battlefield. The success of SIMNET, the disappointment of ACE-89, and the desire to combine existing combat simulations prompted DARPA to initiate research that lead to ALSP. DARPA sponsored the design of a general interface between large, existing, aggregate-level combat simulations. Aggregate-level combat simulations use Lanchestrian models of combat rather than individual physical weapon models and are typically used for high-level training. Despite representational differences, several principles of SIMNET applied to aggregate-level simulations: The ALSP challenge had requirements beyond those of SIMNET: A conceptual framework

2730-488: The US Air Force's Air Warfare Simulation (AWSIM) . The success of the prototype and users' recognition of the value of this technology to the training community led to development of production software. The first ALSP confederation, providing air-ground interactions between CBS and AWSIM, supported three major exercises in 1992. By 1995, ALSP had transitioned to a multi-Service program with simulations representing

2800-616: The US Army (CBS), the US Air Force (AWSIM), the US Navy ( RESA ), the US Marine Corps ( MTWS ), electronic warfare ( JECEWSI ), logistics ( CSSTSS ), and intelligence ( TACSIM ). The program had also transitioned from DARPA's research and development emphasis to mainstream management by the US Army's Program Executive Office for Simulation, Training, and Instrumentation ( PEO STRI ) ALSP developed and demonstrated key aspects of distributed simulation, many of which were applied in

2870-649: The agency shut down its so called "LifeLog Project". The project's aim would have been, "to gather in a single place just about everything an individual says, sees or does". On October 28, 2009, the agency broke ground on a new facility in Arlington County, Virginia a few miles from The Pentagon . In fall 2011, DARPA hosted the 100-Year Starship Symposium with the aim of getting the public to start thinking seriously about interstellar travel. On June 5, 2016, NASA and DARPA announced that it planned to build new X-planes with NASA 's plan setting to create

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2940-498: The agency's research portfolio, and two additional offices that manage special projects. All offices report to the DARPA director, including: A 1991 reorganization created several offices which existed throughout the early 1990s: A 2010 reorganization merged two offices: A list of DARPA's active and archived projects is available on the agency's website. Because of the agency's fast pace, programs constantly start and stop based on

3010-590: The connection between a simulation and its ACM and a method of information exchange between a simulation and its ACM. Two services control distribution of simulation protocol messages: events and dispatches. Event messages are time-stamped and delivered in a temporally-consistent order. Dispatch messages are delivered as soon as possible, without regard for simulation time. Additional protocol messages provide connection state, filter registration, attribute lock control, confederation save control, object resource control, and time control services. The object management protocol

3080-643: The development of HLA. In 1989, the Warrior Preparation Center (WPC) in Einsiedlerhof, Germany hosted the computerized military exercise ACE-89. The Defense Advanced Research Projects Agency ( DARPA ) used ACE-89 as a technology insertion opportunity by funding deployment of the Defense Simulation Internet (DSI). Its packetized video teleconferencing brought general officers of NATO nations face-to-face during

3150-510: The early explorers' discoveries. TRANSIT, sponsored by the Navy and developed under the leadership of Richard Kirschner at Johns Hopkins, was the first satellite positioning system." During the late 1960s, with the transfer of these mature programs to the Services, ARPA redefined its role and concentrated on a diverse set of relatively small, essentially exploratory research programs. The agency

3220-579: The first scientist to administer ARPA, managed to raise its budget to $ 250 million. It was Ruina who hired J. C. R. Licklider as the first administrator of the Information Processing Techniques Office , which played a vital role in creation of ARPANET , the basis for the future Internet. Additionally, the political and defense communities recognized the need for a high-level Department of Defense organization to formulate and execute R&D projects that would expand

3290-665: The foundation of DARPA sensor, surveillance , and directed energy R&D, particularly in the study of radar , infrared sensing, and x-ray / gamma ray detection. ARPA at this point (1959) played an early role in Transit (also called NavSat) a predecessor to the Global Positioning System (GPS). "Fast-forward to 1959 when a joint effort between DARPA and the Johns Hopkins Applied Physics Laboratory began to fine-tune

3360-519: The fourth one. Major approaches are as follows. In this approach, it is assumed that a deadlock will never occur. This is also an application of the Ostrich algorithm . This approach was initially used by MINIX and UNIX . This is used when the time intervals between occurrences of deadlocks are large and the data loss incurred each time is tolerable. Ignoring deadlocks can be safely done if deadlocks are formally proven to never occur. An example

3430-604: The frontiers of technology beyond the immediate and specific requirements of the Military Services and their laboratories. In pursuit of this mission, DARPA has developed and transferred technology programs encompassing a wide range of scientific disciplines that address the full spectrum of national security needs. From 1958 to 1965, ARPA's emphasis centered on major national issues, including space, ballistic missile defense , and nuclear test detection. During 1960, all of its civilian space programs were transferred to

3500-437: The future. One of the most used deadlock avoidance algorithms is Banker's algorithm . A livelock is similar to a deadlock, except that the states of the processes involved in the livelock constantly change with regard to one another, none progressing. The term was coined by Edward A. Ashcroft in a 1975 paper in connection with an examination of airline booking systems. Livelock is a special case of resource starvation ;

3570-489: The general definition only states that a specific process is not progressing. Livelock is a risk with some algorithms that detect and recover from deadlock . If more than one process takes action, the deadlock detection algorithm can be repeatedly triggered. This can be avoided by ensuring that only one process (chosen arbitrarily or by priority) takes action. Distributed deadlocks can occur in distributed systems when distributed transactions or concurrency control

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3640-419: The information necessary to coordinate the transfer of attribute ownership between simulations. An ALSP Broadcast Emulator (ABE) facilitates the distribution of ALSP information. It receives a message on one of its communications paths and retransmits the message on all of its remaining communications paths. This permits configurations where all ALSP components are local to one another (on the same computer or on

3710-496: The kind parameter. The kind parameter has a hierarchical structure similar to the object class structure. The simulation informs its ACM of the interaction kinds that should pass or fail the interaction filter. To minimize message traffic between components in an ALSP confederation, AIS employs a form of intelligent message routing that uses the Event Distribution Protocol (EDP). The EDP allows ACMs to inform

3780-638: The needs of the U.S. government. Structured information about some of the DARPA's contracts and projects is publicly available. DARPA is well known as a high-tech government agency, and as such has many appearances in popular fiction. Some realistic references to DARPA in fiction are as "ARPA" in Tom Swift and the Visitor from Planet X (DARPA consults on a technical threat), in episodes of television program The West Wing (the ARPA-DARPA distinction),

3850-646: The next year. Victoria Coleman became the director of DARPA in November 2020. In recent years, DARPA officials have contracted out core functions to corporations. For example, during fiscal year 2020, Chenega ran physical security on DARPA's premises, System High Corp. carried out program security, and Agile Defense ran unclassified IT services. General Dynamics runs classified IT services. Strategic Analysis Inc. provided support services regarding engineering, science, mathematics, and front office and administrative work. DARPA has six technical offices that manage

3920-443: The object management protocol. Each attribute of each object known to a given ACM has a status that assumes one of three values: From the ACM's perspective, objects come into existence through the registration process performed by its simulation or through the discovery of objects registered by other simulations. The initial state attribute locks for registered objects and discovered objects is as follows: The time management protocol

3990-440: The operating system be given in advance additional information concerning which resources a process will request and use during its lifetime. Deadlock avoidance algorithm analyzes each and every request by examining that there is no possibility of deadlock occurrence in the future if the requested resource is allocated. The drawback of this approach is its requirement of information in advance about how resources are to be requested in

4060-466: The organization first changed from its founding name, ARPA, to DARPA, in March 1972, changing back to ARPA in February 1993, then reverted to DARPA in March 1996. The Economist has called DARPA "the agency that shaped the modern world," with technologies like " Moderna's COVID-19 vaccine ... weather satellites , GPS , drones , stealth technology , voice interfaces , the personal computer and

4130-415: The other AIS components about the update and interaction filters registered by their simulations. In the case of update messages, distribution of this information allows ACMs to only distribute data on classes (and attributes of classes) that are of interest to the confederation. The ABE also use this information to send only information that is of interest to the components it serves. For interaction messages,

4200-498: The process is similar, except that the kind parameter in the interaction message determines where the message is sent. Defense Advanced Research Projects Agency The Defense Advanced Research Projects Agency ( DARPA ) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as

4270-699: The purpose of forming and executing research and development projects to expand the frontiers of technology and science, and able to reach far beyond immediate military requirements. The two relevant acts are the Supplemental Military Construction Authorization ( Air Force ) (Public Law 85-325) and Department of Defense Directive 5105.15, in February 1958. It was placed within the Office of the Secretary of Defense (OSD) and counted approximately 150 people. Its creation

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4340-653: The robot . DARPA also supported the early development of both hypertext and hypermedia . DARPA funded one of the first two hypertext systems, Douglas Engelbart 's NLS computer system, as well as The Mother of All Demos . DARPA later funded the development of the Aspen Movie Map , which is generally seen as the first hypermedia system and an important precursor of virtual reality . The Mansfield Amendment of 1973 expressly limited appropriations for defense research (through ARPA/DARPA) only to projects with direct military application. The resulting " brain drain "

4410-411: The simulation currently owns. For any object class, attributes may be members of Information flow across the network can be further restricted through filters. Filtering provides discrimination by (1) object class, (2) attribute value or range, and (3) geographic location. Filters also define the interactions relevant to a simulation. The ownership and filtering information maintained by the ACM provide

4480-447: The simulation's update message filtering criteria that the simulation provides. As discussed in earlier, when an ACM receives an update message there are four possible outcomes: (1) the ACM discards the message, (2) the ACM sends the simulation a create message, (3) the ACM sends the simulation the update message, or (4) the ACM sends the simulation a delete message. Interaction messages. An ACM may discard interaction messages because of

4550-677: The successful programs were transitioned to the Services, such as the foundation technologies in automatic target recognition , space-based sensing, propulsion, and materials that were transferred to the Strategic Defense Initiative Organization (SDIO), later known as the Ballistic Missile Defense Organization (BMDO), now titled the Missile Defense Agency (MDA). During the 1980s, the attention of

4620-692: The television program Numb3rs , and the Netflix film Spectral . Deadlock avoidance In concurrent computing , deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lock . Deadlocks are a common problem in multiprocessing systems, parallel computing , and distributed systems , because in these contexts systems often use software or hardware locks to arbitrate shared resources and implement process synchronization . In an operating system ,

4690-433: The value of the attribute. Objects not owned by a particular simulation but within the area of perception for the simulation are known as ghosts. Ghosts are local copies of objects owned by other simulations. When a simulation creates an object, it reports this fact to the confederation to let other simulations create ghosts. Likewise, when a simulation deletes an object, it reports this fact to enable ghost deletion. Whenever

4760-556: Was directly attributed to the launching of Sputnik and to U.S. realization that the Soviet Union had developed the capacity to rapidly exploit military technology. Initial funding of ARPA was $ 520 million. ARPA's first director, Roy Johnson, left a $ 160,000 management job at General Electric for an $ 18,000 job at ARPA. Herbert York from Lawrence Livermore National Laboratory was hired as his scientific assistant. Johnson and York were both keen on space projects, but when NASA

4830-452: Was established later in 1958 all space projects and most of ARPA's funding were transferred to it. Johnson resigned and ARPA was repurposed to do "high-risk", "high-gain", "far out" basic research, a posture that was enthusiastically embraced by the nation's scientists and research universities. ARPA's second director was Brigadier General Austin W. Betts, who resigned in early 1961 and was succeeded by Jack Ruina who served until 1963. Ruina,

4900-573: Was renamed the Defense Advanced Research Projects Agency (DARPA) in 1972, and during the early 1970s, it emphasized direct energy programs, information processing, and tactical technologies. Concerning information processing, DARPA made great progress, initially through its support of the development of time-sharing . All modern operating systems rely on concepts invented for the Multics system, developed by

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