TERMS & DEFINITIONS

Thin Client terminology CAN take a bit of getting used to.
Here is a list of words/names that crop up time and again
when talking about Thin Clients and the world in which
they live.

  3G Cards 

Internal 3G data cards are simply mobile broadband modems that are built-in to your laptop with a slot for you to insert your SIM card into. All built-in 3G data cards are HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) enabled so that, as 3G networks are updated and speeds are increased, you’ll continue to get the best possible connection and the fastest possible speeds on your chosen network.

  Citrix (or Citrix Systems, Inc) 

Citrix Systems, Inc. is an American multinational corporation that provides server and desktop virtualization , networking, software-as-a-service (SaaS ) and cloud computing technologies for more than 230,000 organizations worldwide.
Corporate Vision: "A world where anyone can work and play from anywhere".

Citrix has a close relationship with Microsoft:
They obtained a source code license to Microsoft's Windows NT 3.51 and, in 1995, shipped a multiuser version of Windows NT with remote access, known as WinFrame, a unique offering targeting the needs of large enterprises.

During the development of WinFrame for Windows NT 4, Microsoft decided that it did not want to license Windows NT 4 source code to Citrix and threatened to build its own version. After negotiations, Microsoft agreed to license Citrix technology for Windows NT Server 4.0, resulting in Windows Terminal Server Edition. Citrix agreed not to ship a competing product but retained the right to sell an extension to Microsoft's products, initially under the name MetaFrame. This relationship continued into the Windows 2000 Server and Windows Server 2003 eras, with Citrix offering Metaframe XP and Presentation Server. On February 11, 2008, Citrix changed the name of its Presentation Server product line to XenApp.

The core technology that Microsoft did not buy was the ICA protocol. Microsoft derived the work for RDP (T.share) protocol from NetMeeting which was originally derived from a deal with PictureTel (now known as Polycom).

Citrix ICA:

Independent Computing Architecture (ICA) is a proprietary protocol for an application server system, designed by Citrix Systems. The protocol lays down a specification for passing data between server and clients, but is not bound to any one platform.

Practical products conforming to ICA are Citrix's WinFrame, Citrix XenApp (formerly called MetaFrame/Presentation Server), and Citrix XenDesktop products. These permit ordinary Windows applications to be run on a suitable Windows server, and for any supported client to gain access to those applications. Besides Windows, ICA is also supported on a number of Unix server platforms and can be used to deliver access to applications running on these platforms. The client platforms need not run Windows; for example, there are clients for Mac, Unix, Linux, and various Smartphones. ICA client software is also built into various thin client platforms.

Citrix XenApp (formerly Citrix MetaFrame Server and Citrix Presentation Server) :

An application virtualization/application-delivery product that allows users to connect to their corporate applications. XenApp can either host applications on central servers and allow users to interact with them remotely or stream and deliver them to user devices for local execution.

  Client

An application or system that accesses a remote service on another computer system, known as a server, by way of a network.  The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing mainframe computer.

The client–server model is still used today on the Internet, where a user may connect to a service operating on a remote system through the Internet protocol suite. Web browsers are clients that connect to web servers and retrieve web pages for display. Most people use e-Mail clients to retrieve their e-Mail from their internet service provider's mail storage servers. Online chat uses a variety of clients, which vary depending on the chat protocol being used. Game Clients usually refer to the software that is the game in only multiplayer online games for the computer.

Increasingly, existing large client applications are being switched to websites, making the browser a sort of universal client. This avoids the hassle of downloading a large piece of software onto any computer you want to use the application on. An example of this is the rise of webmail.

Clients are generally classified as either "fat clients", "thin clients", or "hybrid clients":

Fat Clients:

A fat client, also known as a rich client or thick client, is a client that performs the bulk of any data processing operations itself, and does not necessarily rely on the server. The fat client is most common in the form of a personal computer, as the personal computers or laptops can operate independently.

Thin Clients:

A thin client is a minimal sort of client. Thin clients use the resources of the host computer. A thin client's job is generally just to graphically display pictures provided by an application server, which performs the bulk of any required data processing. Programming environments for thin clients include JavaScript/AJAX (client side automation), ASP, JSP, Ruby on Rails, Python's Django, PHP and other (depends on server-side backend and uses HTML pages or rich media like Flash, Flex or Silverlight on client).  (For more on Thin Clients, go here .)

Hybrid Clients:

A hybrid client is a mixture of the above two client models. Similar to a fat client, it processes locally, but relies on the server for storage data. This approach offers features from both the fat client (multimedia support, high performance) and the thin client (high manageability, flexibility)..

  Cloud Computing

Internet-based computing, whereby shared resources, software and information are provided to computers and other devices on-demand, like a public utility.

The term cloud is used as a metaphor for the Internet, based on the cloud drawing used in the past to represent the telephone network, and later to depict the Internet in computer network diagrams as an abstraction of the underlying infrastructure it represents. Typical cloud computing providers deliver common business applications online which are accessed from another web service or software like a web browser, while the software and data are stored on servers.

Most cloud computing infrastructure consists of reliable services delivered through data centers and built on servers. Clouds often appear as single points of access for all consumers' computing needs. Commercial offerings are generally expected to meet quality of service (QoS) requirements of customers and typically offer SLAs.

  Ethernet

Ethernet is a family of frame-based computer-networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer.

Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber-optic versions for site back-bones, is the most widespread wired LAN technology. It has been in use from around 1980 to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET.

  Fat Client (Also called a Server)

A computer designed to fulfill traditional computational roles.

  File Transfer Protocol (FTP)

A standard network protocol used to copy a file from one host to another over a TCP/IP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server applications which solves the problem of different end-host configurations (i.e. Operating System, file names).  FTP is used with user-based password-authentication or with anonymous user access.

Applications were originally interactive command-line tools with a standardized command syntax, but graphical user interfaces (GUI's) have been developed for all desktop operating systems in use today.

  Firewall (IP-Blocking)

Control access to private networks based on the public IP of the client. Whether using a blacklist or a whitelist, the IP address that is blocked is the perceived public IP address of the client, meaning that if the client is using a proxy server or NAT, blocking one IP address might block many individual people.

  Gateway

A network node equipped for interfacing with another network that uses different protocols.
Routers exemplify special cases of gateways.

  Hyper-V

Microsoft Hyper-V, formerly known as Windows Server Virtualization, is a hypervisor -based virtualization system for x64 computers.  The finalized version (automatically updated through Windows Update) was released on June 26th 2008. Hyper-V has since also been released in a free stand-alone version, and has been upgraded to Release 2 (R2) status.

  Hypervisor

A hypervisor, also called Virtual Machine Monitor (VMM), allows multiple operating systems to run concurrently on a host computer — a feature called hardware virtualization . The hypervisor presents the guest operating systems with a virtual platform and monitors the execution of the guest operating systems. In that way, multiple operating systems, including multiple instances of the same operating system, can share hardware resources. Unlike multitasking, which also allows applications to share hardware resources, the virtual machine approach using a hypervisor isolates failures in one operating system from other operating systems sharing the hardware.

An example of a Hypervisor is PR/SM (Processor Resource/System Manager), which is a type-1 Hypervisor that allows multiple logical partitions (LPARs) to share physical resources such as CPUs, direct access storage devices (DASD), and memory. PR/SM was introduced by IBM in the early 1970's with the IBM System 370 processors. These concepts have become an important part of the term known as Virtualization .

  Independent Computing Architecture (ICA )

Independent Computing Architecture (ICA) is a proprietary protocol for an application server system, designed by Citrix Systems. The protocol lays down a specification for passing data between server and clients, but is not bound to any one platform.

Practical products conforming to ICA are Citrix's WinFrame, Citrix XenApp (formerly called MetaFrame/Presentation Server), and Citrix XenDesktop products. These permit ordinary Windows applications to be run on a suitable Windows server, and for any supported client to gain access to those applications. Besides Windows, ICA is also supported on a number of Unix server platforms and can be used to deliver access to applications running on these platforms. The client platforms need not run Windows; for example, there are clients for Mac, Unix , Linux , and various Smartphones. ICA client software is also built into various thin client platforms.

ICA is broadly similar in purpose to window servers such as the X Window System. It also provides for the feedback of User input from the client to the server, and a variety of means for the server to send graphical output, as well as other media such as audio, from the running application to the client.

  Internet Message Access Protocol (IMAP)

The Internet Message Access Protocol (IMAP) is one of the two most prevalent Internet standard protocols for e-Mail retrieval, the other being the Post Office Protocol (POP).  Virtually all modern e-Mail clients and mail servers support both protocols as a means of transferring e-Mail messages from a server.

  Internet Protocol (IP)

The Internet Protocol (IP) is a protocol used for communicating data across a packet-switched internetwork using the Internet Protocol Suite, also referred to as TCP/IP.

IP is the primary protocol in the Internet Layer of the Internet Protocol Suite and has the task of delivering distinguished protocol datagrams (packets) from the source host to the destination host solely based on their addresses. For this purpose the Internet Protocol defines addressing methods and structures for datagram encapsulation. The first major version of addressing structure, now referred to as Internet Protocol Version 4 (IPv4) is still the dominant protocol of the Internet, although the successor, Internet Protocol Version 6 (IPv6) is being deployed actively worldwide.

  Internet Protocol (IP) Address

A numerical label that is assigned to devices participating in a computer network, that uses the Internet Protocol for communication between its nodes. An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name  indicates what we seek. An address indicates where it is. A route indicates how to get there."

The designers of TCP/IP defined an IP address as a 32-bit number and this system, known as Internet Protocol Version 4 or IPv4, is still in use today. However, due to the enormous growth of the Internet and the resulting depletion of available addresses, a new addressing system (IPv6), using 128 bits for the address, was developed in 1995 and last standardized by RFC 2460 in 1998. Although IP addresses are stored as binary numbers, they are usually displayed in human-readable notations, such as 208.77.188.166 (for IPv4), and 2001:db8:0:1234:0:567:1:1 (for IPv6).

The Internet Protocol also routes data packets between networks; IP addresses specify the locations of the source and destination nodes in the topology of the routing system. For this purpose, some of the bits in an IP address are used to designate a subnetwork. The number of these bits is indicated in CIDR notation, appended to the IP address; e.g., 208.77.188.166/24.

As the development of private networks raised the threat of IPv4 address exhaustion, RFC 1918 set aside a group of private address spaces that may be used by anyone on private networks. They are often used with network address translators to connect to the global public Internet.

The Internet Assigned Numbers Authority (IANA), which manages the IP address space allocations globally, cooperates with five Regional Internet Registries (RIRs) to allocate IP address blocks to Local Internet Registries (Internet Service Providers or ISP's) and other entities.

 

  Kiosk

An Interactive Kiosk is a computer terminal that provides information access via electronic methods. Most kiosks provide unattended access to web applications and are typically placed in high foot traffic settings such as hotel lobbies or airports.

Integration of technology allows kiosks to perform a wide range of functions, evolving into self-service kiosks. For example, kiosks may enable users to enter a public utility bill account number in order to perform an online transaction, or collect cash in exchange for merchandise. Customised components such as coin-hoppers, bill-acceptors, card-readers and thermal printers enable kiosks to meet the owner's specialised needs.

  Local Area Network (LAN)

A computer network covering a small physical area, like a home, office, or small group of buildings, such as a school or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.

ARCNET, Token Ring and many other technologies have been used in the past, and G.hn may be used in the future, but Ethernet over twisted pair cabling, and Wi-Fi are the two most common technologies currently in use.

  Linux

                                          © Larry Ewing, Simon Budig & Anja Gerwinski

A generic term referring to Unix -like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed, both commercially and non-commercially, by anyone under licenses such as the GNU General Public License.

Linux can be installed on a wide variety of computer hardware, ranging from embedded devices such as mobile phones, smartphones and wristwatches to mainframes and supercomputers. Linux is predominantly known for its use in servers; a 2008 estimate suggested that 60% of all web servers ran Linux. Most desktop computers run either Mac OS X or Microsoft Windows, with Linux having only 1–2% of the desktop market. However, desktop use of Linux has become increasingly popular in recent years.

  MAC Address (Media Access Control Address)

A unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sub-layer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address.

  Microsoft Remote Desktop Protocol (RDP)

A proprietary protocol developed by Microsoft, which concerns providing a user with a graphical interface to another computer. Clients exist for most versions of Microsoft Windows (including Windows Mobile), Linux, Unix, Mac OS X  and other modern operating systems. By default the server listens on TCP port 3389.
Microsoft currently refers to their official RDP server software as Remote Desktop Services, formerly "Terminal Services". Their official client software is currently referred to as Remote Desktop Connection, formerly "Terminal Services Client".

  Multicast Addressing

A network technology for the delivery of information  to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the multiple destinations split.
The word "multicast" is typically used to refer to IP multicast which is often employed for streaming media and Internet television applications.

  Network Address Translation (NAT)

The process of modifying network address information in datagram (IP) packet headers while in-transit across a traffic routing device for the purpose of remapping a given address space into another.

NAT is usually used in conjunction with network masquerading (or IP masquerading) which is a technique that hides an entire address space, usually consisting of private network addresses (RFC 1918), behind a single IP address in another, often public address space. This mechanism is implemented in a routing device that uses stateful translation tables to map the "hidden" addresses into a single address and then rewrites the outgoing Internet Protocol (IP) packets on exit so that they appear to originate from the router.

  Network Interface Card (NIC)

A network interface card is used to connect a computer to an Ethernet  network. The card provides an interface to the media either using an external transceiveror through an internal integrated transceiver mounted on the network interface card Printed Circuit Board (PCB). The card usually contains the protocol control firmware and Ethernet Controller needed to support the Medium Access Control (MAC) data link protocol used by Ethernet.

Each NIC is assigned an Ethernet source address by the NIC's manufacturer, normally stored in a PROM (Programmable Read Only Memory) on the NIC. The addresses are globally unique, and are assigned in blocks of 16 (or 8) million address to the Ethernet interface manufacturers, according to a flat addressing structure. This ensures that no two Ethernet network interface will ever have the same source address.

  Peer-to-Peer (P2P)

Any distributed network architecture composed of participants that make a portion of their resources (such as processing power, disk storage or network bandwidth) directly available to other network participants, without the need for central coordination instances (such as servers or stable hosts). Peers are both suppliers and consumers of resources, in contrast to the traditional client–server model where servers supply and clients consume.

Peer-to-peer was popularized by file-sharing systems like Napster. Peer-to-peer file-sharing networks have inspired new structures and philosophies in other areas of human interaction. In such social contexts, peer-to-peer as a meme refers to the egalitarian social networking that is currently emerging throughout society, enabled by Internet technologies in general.

  Ping

A network administration utility used to test whether a particular host is reachable across an Internet Protocol (IP) network and to measure the round-trip time for packets sent from the local host to a destination computer, including the local host's own interfaces.

  Post Office Protocol (POP)

An application-layer Internet standard protocol used by local e-Mail clients to retrieve e-Mail from a remote server over a connection. POP and TCP/IP IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-Mail retrieval. Virtually all modern e-Mail clients and servers support both. The POP protocol has been developed through several versions, with version 3 (POP3) being the current standard.

  Private Network

A network that uses private IP address space, following the standards set by RFC 1918 and RFC 4193. These addresses are commonly used for home, office, and enterprise local area networks (LANs), when globally routable addresses are not mandatory, or are not available for the intended network applications. Private IP address spaces were originally defined in an effort to delay IPv4 address exhaustion, but they are also a feature of the next generation Internet Protocol, IPv6 .

These addresses are characterized as private because they are not globally delegated, meaning they are not allocated to any specific organization, and IP packets addressed by them cannot be transmitted onto the public Internet. Anyone may use these addresses without approval from a regional Internet registry (RIR). If such a private network needs to connect to the Internet, it must use either a network address translator (NAT) gateway , or a proxy server .

The most common use of these addresses is in residential networks, since most Internet service providers (ISPs) only allocate a single routable IP address to each residential customer, but many homes have more than one networked device, for example, several computers and a video game console. In this situation, a NAT gateway is usually used to enable Internet connectivity to multiple hosts. Private addresses are also commonly used in corporate networks, which for security reasons, are not connected directly to the Internet.

Because many private networks use the same private IP address space, a common problem occurs when merging such networks, the collision of address space, i.e. the duplication of addresses on multiple devices. In this case, networks must be renumbered, often a time-consuming task, or a NAT router must be placed between the networks to masquerade the duplicated addresses.

  Proxy Server

A server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. A proxy server may optionally alter the client's request or the server's response, and sometimes it may serve the request without contacting the specified server. In this case, it 'caches' responses from the remote server, and returns subsequent requests for the same content directly.

A proxy server has many potential purposes, including:

    * To keep machines behind it anonymous (mainly for security).
    * To speed up access to resources (using caching). Web proxies are commonly used to cache web pages from a web server.
    * To apply access policy to network services or content, e.g. to block undesired sites.
    * To log / audit usage, i.e. to provide company employee Internet usage reporting.
    * To bypass security/ parental controls.
    * To scan transmitted content for malware before delivery.
    * To scan outbound content, e.g., for data leak protection.
    * To circumvent regional restrictions.

A proxy server that passes requests and replies unmodified is usually called a gateway or sometimes tunneling proxy.

A proxy server can be placed in the user's local computer or at various points between the user and the destination servers on the Internet.

  Remote Desktop Connection (RDC)

Remote Desktop Connection is a technology that allows you to sit at a computer (sometimes called the client computer) and connect to a remote computer (sometimes called the host computer) in a different location. For example, you can connect to your work computer from your home computer and have access to all of your programs, files, and network resources as though you were in front of your computer at work. You can leave programs running at work and then, when you get home, you can see your work computer's desktop displayed on your home computer, with the same programs running.

RDC 7.0 (compatible with Windows Vista SP1 & 2 and XP SP3) became available in Q4 of 2009.

  Remote Desktop (or Display) Protocol (RDP)

  Remote Desktop Services

  Service Level Agreement (SLA)

Part of a service contract where the level of service is formally defined. 

Software-as-a-Service (SaaS)

A model of software deployment over the internet. With SaaS, a provider licenses an application to customers for use as a service-on-demand, either through a time-subscription or a “pay-as-you-go” model. Rather than purchase the hardware and software to run an application, customers need only a computer or a server to download the application and internet access to run the software. The software can be licensed for a single user or for a group of users.

SaaS software vendors may host the application on their own web servers or upload the application to the consumer device, disabling it after use or after the on-demand contract expires. SaaS use has become commonplace by businesses for tasks such as computerized billing, invoicing, human resource management, service desk management, and sales pipeline management, etc.

  Secure Shell (SSH)

A network protocol that allows data to be exchanged using a secure channel between two networked devices. Used primarily on GNU/Linux and Unix based systems to access shell accounts, SSH was designed as a replacement for Telnet and other insecure remote shells, which send information, notably passwords, in plaintext, rendering them susceptible to packet analysis. The encryption used by SSH provides confidentiality and integrity of data over an insecure network, such as the Internet.

  Server

Any combination of hardware or software designed to "provide services" to clients. When used alone, the term typically refers to a computer which may be running a server operating system, but is also used to refer to any software or dedicated hardware capable of providing services.

In the hardware sense, the word server typically designates computer models intended for running software applications  under the heavy demand of a network environment. In this client–server configuration one or more machines, either a computer or a computer appliance, share information with each other with one acting as a host for the other.

  SoThin Connection Manager

The SoThin Connection Manager allows you to add local programs, Microsoft RDP /RDC , Citrix , Virtual servers / desktops and Tarantella connections as well as creating your own custom connections, allowing you to extend the useable lifecycle of your Windows computers.

  SoThin Thin Client

SoThin Thin Client is an application which is designed to replace the Windows Shell with the SoThin Connection Manager on Windows PCs and Laptops – in essence turning your PCs and laptops into Thin Clients . The SoThin Connection Manager allows you to add local programs, Microsoft RDP /RDC , Citrix , Virtual servers / desktops and Tarantella connections as well as creating your own custom connections. This allows you to extend the useable lifecycle of your PCs and Laptops and negates the requirement for hardware Thin Clients to be purchased when an organisation decides to move to a Thin Client environment.  

  Telnet

A network protocol used on the Internet or local area network s to provide a bidirectional interactive text-oriented communications facility via a virtual terminal connection. User data is interspersed in-band with TELNET control information in an 8-bit byte oriented data connection over the Transmission Control Protocol (TCP).

Historically, telnet provided access to a command-line interface (usually, of an operating system) on a remote host. Most network equipment and operating systems with a TCP/IP stack support a Telnet service for remote configuration (including systems based on Windows NT). Because of security issues with Telnet, its use for this purpose has waned in favor of SSH.

  Transmission Control Protocol (TCP)

TCP is one of the two original components of the Internet Protocol Suite (the other being Internet Protocol, or IP), so the entire suite is commonly referred to as TCP/IP. Whereas IP handles lower-level transmissions from computer to computer as a message makes its way across the Internet, TCP operates at a higher level, concerned only with the two end-systems (eg: a Web browser and a Web server). In particular, TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer. Besides the Web, other common applications of TCP include e-Mail and file transfer. Among its other management tasks, TCP controls segment-size, flow-control, the rate at which data is exchanged, and network traffic congestion.

  Tarantella

A division of Oracle.

They produce and sell the Sun Secure Global Desktop range of terminal services applications, formerly known as Tarantella and Canaveral iQ. In 2005 Sun licensed the Microsoft Windows Terminal Server-based Tarantella product to the UK-based company ProPalms, which directly competes as a lower-cost alternative to Citrix Metaframe.

  Thin Client (Sometimes called a Lean or Slim Client)

A computer or a computer program which depends heavily on some other computer (it's server) to fulfill its traditional computational roles. Thin clients occur as components of a broader computer infrastructure, where many clients share their computations with the same server. 

Cheap client hardware:

While the server must be robust enough to handle several client sessions at once, thin clients can be made out of much cheaper hardware than a fat client can. This reduces the power consumption of those clients, and makes the system marginally scalable: it is relatively cheap to add on a couple more client terminals. Typical thin clients tend to have a very low total-cost-of-ownership (TCO), but some of that is offset by requiring a robust server infrastructure with backups and so forth. This is also reflected in terms of power consumption: thin clients generally use very little power and might not even require cooling fans, but the servers are higher-power and require an air-conditioned server room.

On the other hand, while the TCO is low, the individual performance of the clients is also low. Thin clients, for example, are not suited to any real form of distributed computing. The costs of compiling software, rendering video, or any other computationally-intensive task will be shared by all clients via the server.

Client simplicity:

Since thin clients are typically made from low-cost hardware with few moving parts, they can operate in more hostile environments than conventional computers. However, they inevitably need a network connection to their server, which must be isolated from such hostile environments. Since thin clients are cheap, they offer a low risk of theft in general, and are easy to replace when they are stolen or broken. Since they don't have any complicated boot images, the problem of boot image control is centralized to the central servers.

On the other hand, to achieve this simplicity, thin clients are generally highly integrated systems. This means that they may lag behind thick clients in terms of extensibility and accessibility. For example, if the server does not have support for independent audio streams, or the communication protocols don't transfer such streams, one simply cannot receive audio from the server. Similarly, if the client lacks USB ports, or if there is some communication failure of its USB signals over the network, the client might be wholly unable to support an unexpected USB peripheral.

Ultra-Thin Clients:

Traditionally, a thin client ran a full operating system for the purposes of connecting to other computers. A newer trend is sometimes called an ultra-thin client or a zero client, which no longer runs a full operating system: the kernel instead merely initializes the network, begins the networking protocol, and handles display of the server's output

  Unix

A computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.

  Virtualization

Execution of software in an environment separated from the underlying hardware resources.

  Virtual Desktop Infrastructure (VDI)

VDI refers to the process of running an End-User desktop inside a virtual machine that lives on a server in a datacenter. It’s a powerful form of desktop virtualization because it enables fully personalized desktops for each End-User with all the security and simplicity of centralized management. 

It’s important to understand, however, that VDI is only one form of desktop virtualization. Most companies have a broad diversity of Users, including task workers, power-users, guest workers, contractors, and mobile employees.

  Virtual Machine (VM)

A software (possibly hardware-assisted) implementation of a machine (computer) that executes programs as if it were a real machine. One physical machine can play host to several virtual machines, each running it's own Operating System.

  Virtual Network Computing (VNC)

A graphical desktop sharing system that uses the RFB protocol to remotely control another computer. It transmits the keyboard and mouse events from one computer to another, relaying the graphical screen updates back in the other direction, over a network.

VNC is platform-independent – a VNC viewer on one operating system may connect to a VNC server on the same or any other operating system. There are clients and servers for many GUI-based operating systems and for Java. Multiple clients may connect to a VNC server at the same time. Popular uses for this technology include remote technical support and accessing files on one's work computer from one's home computer, or vice versa.

VNC was originally developed at the Olivetti Research Laboratory in Cambridge, United Kingdom. The original VNC source code and many modern derivatives are open source under the GNU General Public License.

  Virtual Private Network (VPN)

A computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network(s), such as the Internet.

  VMWare

VMware, Inc. is a provider of virtualization software. The company was founded in 1998 and is based in Palo Alto, California. The Company is majority owned by EMC Corporation.

VMware's desktop software runs on Microsoft Windows, Linux , and Mac OS X. VMware's enterprise software, VMware ESX Server, runs directly on server hardware without requiring an additional underlying operating system.

  Wide Area Network (WAN)

  Windows Shell

The Windows shell is the main graphical user interface in Microsoft Windows. The Windows shell includes well-known Windows components such as the Taskbar and the Start menu. The process that hosts the Windows shell is Explorer.exe . The Windows shell is not a "shell" in the usual sense of the term, and the word here is used more generally.

Since the introduction of Windows 95, the Shell has included the Taskbar and the Start Button (which replaced Program Manager), plus several system folders: My Computer, Network Neighborhood and the Recycle Bin, with Windows Explorer replacing File Manager. Windows XP and Server 2003 introduced the Control Panel. The Aero User Interface was built into most Vista andServer 2008 machines and is now included in Windows 7, in which it introduced new UI gestures such as Aero Peek, Aero Snap, Aero Shake, thumbnail-based switching and Alt+Tab enhancements.

It is possible to replace the default Windows shell with a different program, which is exactly what  SoThin Thin Client does. There exist a number of third party shells designed to be used in place of the standard Windows shell.

  Windows Terminal Server

Remote Desktop Services, formerly known as Terminal Services, is one of the components of Microsoft Windows (both server and client versions) that allows a user to access applications and data on a remote computer over a network.
Terminal Services is Microsoft's implementation of thin-client terminal server computing, where Windows applications, or even the entire desktop of the computer running terminal services, are made accessible to a remote client machine. The client can either be a fully-fledged computer, running any operating system as long as the terminal services protocol is supported, or a bare-bones machine powerful enough to support the protocol (such as Windows FLP).
With terminal services, only the user interface of an application is presented at the client machine. Any input to it is redirected over the network to the server, where all application execution takes place. (This is in contrast to appstreaming systems, like Microsoft Application Virtualization, in which the applications, while still stored on a centralized server, are streamed to the client on-demand and then executed on the client machine.)

  Workstation

A high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network (LAN) and run multi-user operating systems. The term workstation is also used to refer to a mainframe computer terminal or to a PC connected to a network.

  XenApp

See Citrix XenApp .

  XenDesktop

As the Citrix people will tell you: "Citrix XenDesktop™ is a desktop virtualization and VDI (Virtual Desktop Infrastructure) solution that delivers a complete Windows desktop experience as an on-demand service to any User, anywhere. Whether users are task workers, knowledge workers or mobile workers, XenDesktop can quickly and securely deliver individual applications or complete desktops while providing a high-definition User experience".