Unsorted computing-related terms:

And this page contains important computing-related terms, definitions, information, but also short explanations (and only the short ones). Again, same as in other similar pages on my site (especially articles, hints, rules etc.), the page contains and will contain the "personal" ones (terms, definitions, info that I've wrote), as well as others that I've found browsing the web and reading articles written by others. But note, for the non-personal ones, they will at least contain modified text, i.e. the text that I wrote in my own words (and not just copied and pasted the text written by someone else), while usually the general point remains the same as in the original article.


VARIOUS COMPUTING/SYSTEM RELATED TERMS:


Page Fault

When a program tries to access some address that is not currently in physical RAM, it generates an interrupt, called a Page Fault.


WINDOWS XP HELP and SUPPORT


Format

The structure of a file that defines the way it is stored and laid out on the screen or in print. The format of a file is usually indicated by its extension. For example, .txt after a file name indicates the file is a text document, and .doc after a file name indicates it is a Word document.


WINDOWS CE - KERNEL EXPLANATION


Controls

A control is a child window that an application uses in conjunction with another window to perform I/O tasks. Common controls are a set of windows that are supported by the common control library, which is a dynamic-link library (DLL) that is included with Windows.


PROCESS EXPLORER - HELP FILE


Handles

System Resource Handles - Files, Registry keys, Synchronization Objects

Relocated DLLs

DLLs that are not loaded at their programmed base address. They cannot load at their base address because other files are already mapped there are relocated by the loader, which consumes CPU and makes parts of the DLL that are modified as part of the relocation un-sharable.


DEFRAG - HELP FILE


Batch Program

An ASCII (unformatted text) file that contains one or more operating system commands. A batch program's file name has a .cmd or .bat extension. When you type the file name at the command prompt, or when the batch program is run from another program, its commands are processed sequentially. Batch programs are also called batch files

Script

A type of program consisting of a set of instructions to an application or tool program. A script usually expresses instructions by using the application's or tool's rules and syntax, combined with simple control structures such as loops and if/then expressions. "Batch program" is often used interchangeably with "script" in the Windows environment.


PEST PATROL - HELP FILE


Program

Windows can run many programs at the same time, but with just a single CPU, can only perform one task at a time. In your computer, Windows gives the illusion that several programs are running in parallel by switching rapidly from one to the next, giving each a time-slice of the CPU. But if any program hangs, Windows may get stuck on that task, and be unable to switch to the other running programs, causing everything to hang.

Process/Task

A task or process is a program (such as an exe file) that is being executed or run. When a program is started, Windows loads it into memory (RAM), adds it to an internal list of running processes, and provides the process with the memory and other resources it needs. Windows tracks what processes are using what resources, and when one of these processes is terminated, Windows can usually return its resources to the general pool, for redistribution to other processes.


PROCESS GUARD - HELP FILE


Process Guard doesn't only protect processes, it also protects all modules and threads belonging to protected processes. So what are processes, modules and threads?

Processes

A process is a logical task. Processes are created when an application runs and when a subsystem or system service is started. Each process has its own dedicated set of resources (such as its own dedicated memory space) that can be accessed directly only by the program that owns the process. This means if you create a program that uses some data, only your program can access that data, unless you set up some form of cross-process communication or take advantage of the operating system's cross-process data-sharing mechanism.

Modules

A module or Dynamically Linked Library (DLL) is an executable module that contain functions and data. DLLs provide a way to modularize applications so they can be loaded, updated, and reused more easily. They also help reduce memory overhead when several applications use the same functionality at the same time, because although each application gets its own copy of the data, they can share the code.

Threads

A thread is a task that can run independently of other parts of the program. A thread belongs to one process and gets its own CPU time slice. Win32-based applications can use multiple threads of execution, which is called multithreading. Win32-based applications can create multiple threads within a given process. By creating multiple threads, the application can accomplish some background processing, such as a calculation, to allow the program to run faster. While the thread is running, the user can continue to interact with the program.


DR.WATSON - HELP FILE


Systemroot

The path and folder name where the Windows system files are located. Typically, this is C:\Windows, although you can designate a different drive or folder when you install Windows. You can use the value %systemroot% to replace the actual location of the folder that contains the Window system files. To identify your systemroot folder, click Start, click Run, type %systemroot%, and then click OK.

Variable

In programming, a named storage location capable of containing a certain type of data that can be modified during program execution. System environment variables are defined by Windows 2000 Server and are the same no matter who is logged on to the computer. Administrator group members can add new variables or change the values, however. User environment variables can be different for each user of a particular computer. They include any environment variables you want to define or variables defined by your applications, such as the path where application files are located.

Environment Variable

A string consisting of environment information, such as a drive, path, or file name, associated with a symbolic name that can be used by Windows. You use System in Control Panel or the set command from the command prompt to define environment variables.

String

A group of characters or character bytes handled as a single entity. Computer programs use strings to store and transmit data and commands. Most programming languages consider strings (such as 2674:gstmn) as distinct from numeric values (such as 470924).

Transmitting station ID (TSID) string

A string that specifies the transmitter subscriber ID sent by the fax machine when sending a fax to a receiving machine. This string is usually a combination of the fax or telephone number and the name of the business. It is often the same as the called subscriber ID.

Called subscriber ID (CSID) string

A string that specifies the called subscriber ID transmitted by the receiving fax machine when receiving an inbound fax. This string is usually a combination of the fax or telephone number and the name of the business. It is often the same as the transmitter subscriber ID.


2XEXPLORER's SITE - "32-bit OPERATING SYSTEMS"


Low-level Kernel Objects

Including files, threads, processes, events, mutexes, semaphores, file mapping etc.

Multi-threaded Applications

Proper inter-thread communication and sunchronization for accessing shared resources.

Inter-process communication

Including data transfer via the clipboard, drag-drop, shared memory files etc.

Shell Namespace Management

File types and associations, file sharing and security, plus general low-level file management.

COM Architecture

I have both used available COM objects and developed my own, with MFC and ATL. I am familiar with a large number of fundamental COM interfaces.


2XEXPLORER's SITE - "USER INTERFACE ELEMENTS"


Windows and Dialogs

I am familiar with "low" level details as window styles, children and parents, plus basic operations like moving/resizing, notifications etc.

Window procedures

Message exchange mechanism between the system and individual windows, the role of a window procedure. WM_xxx messages.

Standard and common controls

I have worked with nearly every type of predefined control and I am aware of the capabilities and limitations of each one of them. I observe closely new features added to the common control library with every new release of Internet Explorer.

Window Subclassing

I understand how to override the default behaviour of system control windows, coercing it to fit into my own specifications, through either permanent or temporary subclassing.


TASKMANAGER - HELP FILE


Processes

An executable program, such as Windows Explorer, or a service, such as MSTask.

Threads

An object within a process that runs program instructions. Threads allow concurrent operations within a process and enable one process to run different parts of its program on different processors simultaneously.

Handles

A value used to uniquely identify a resource, such as a file or registry key, so that a program can access it.

Commit

Memory allocated to programs and the system. Because of virtual memory, the value listed under Commit Peak memory may exceed the maximum physical memory.

Physical

The physical memory installed on your computer.

Memory or RAM

The area of your computer that contains information needed by running programs.

Kernel

The core of layered architecture that manages the most basic operations of the operating system and the computer's processor. The kernel schedules different blocks of executing code, called threads, for the processor to keep it as busy as possible and coordinates multiple processors to optimize performance. The kernel also synchronizes activities among Executive-level subcomponents, such as I/O Manager and Process Manager, and handles hardware exceptions and other hardware-dependent functions. The kernel works closely with the hardware abstraction layer.


NORTON UTILITIES - HELP FILE


Windows Service

A program that performs a specific task to support other programs) and error messages.

Swap File 1

A hidden file that Windows uses as virtual memory. The swap file temporarily holds information from RAM in order to free RAM for use by other applications. The Windows 98 and Windows Me swap file is named WIN386.SWP. Under Windows NT, Windows 2000, and Windows XP, the swap file is called a "paging file," and is named PAGEFILE.SYS.

Swap File 2

The Windows swap file is used for temporary data storage to increase the effective size of your computer's physical memory (RAM). By default, Windows changes the size of the swap file dynamically, to meet changing system conditions. An unfortunate side effect is increased disk fragmentation, which can hurt computer performance. Setting a minimum size for the swap file can reduce or eliminate swap file fragmentation, and, secondarily, slow the normal disk fragmentation process. Norton Optimization Wizard examines your system and sets an efficient minimum swap file size. It also moves the swap file to your fastest drive.

Fragment

When the data that makes up a file is stored to non-contiguous locations across a disk, the file is said to be fragmented; each file fragment is a non-contiguous cluster containing a portion of the file. Fragmentation occurs during the normal processes of creating, modifying, copying, moving, and deleting files. Fragmented information takes longer to read from the disk than unfragmented information because it requires more movement from the disk drive’s read/write head. Fragmentation can also impede recovery of deleted files. See also defragment.

Registry Files

The registry is a database used by Windows and other applications to store hardware and software configuration information. The registry is vital to Windows, and the efficiency of data storage in the registry can have an impact on computer performance. Norton Optimization Wizard reorganizes registry data for efficient storage and retrieval, improving the performance of Windows and your software applications.

Registry

A Windows database that provides centralized storage of startup, configuration, and other information. The registry stores information about all installed hardware and any software that has been designed expressly for the Windows operating system. The registry is one of the components that enables Windows to support Plug and Play, and is organized into catagories called "registry keys." The registry replaces many of the Windows 3.x functions previously provided by the AUTOEXEC.BAT, CONFIG.SYS, WIN.INI, and SYSTEM.INI files, and by individual applications’ INI files These files may still exist in Windows to provide backward compatibility for any hardware or software needing them. The registry stores its information in two binary files: SYSTEM.DAT, which maintains up-to-date computer-related data, and USER.DAT, which can maintain multiple system configurations for different users or purposes.

---

VARIOUS INTERNET RELATED TERMS:


DHCP - FAQ SITE


DHCP lease

A DHCP lease is the amount of time that the DHCP server grants to the DHCP client permission to use a particular IP address. A typical server allows its administrator to set the lease time.

IP address

An IP address (also called an IP number) is a number (typically written as four numbers separated by periods, i.e. 107.4.1.3 or 84.2.1.111) which uniquely identifies a computer that is making use of the Internet. It is analogous to your telephone number in that the telephone number is used by the telephone network to direct calls to you. The IP address is used by the Internet to direct data to your computer, e.g. the data your web browser retrieves and displays when you surf the net. One task of DHCP is to assist in the problem of getting a functional and unique IP number into the hands of the computers that make use of the Internet.

MAC address

A MAC address (also called an Ethernet address or an IEEE MAC address) is a number (typically written as twelve hexadecimal digits, 0 through 9 and A through F, or as six hexadecimal numbers separated by periods or colons, i.e. 0080002012ef, 0:80:0:2:20:ef) which uniquely identifes a computer that has an Ethernet interface. Unlike the IP number, it includes no indication of where your computer is located. In DHCP's typical use, the server uses a requesting computer's MAC address to uniquely identify it.

Client ID

What is termed the Client ID for the purposes of the DHCP protocol is whatever is used by the protocol to identify the client computer. By default, DHCP implementations typically employ the client's MAC address for this purpose, but the DHCP protocol allows other options. Some DHCP implementations have a setup option to specify the client ID you want. One alternative to the MAC address is simply a character string of your choice. In any case, in order for DHCP to function, you must be certain that no other client is using the client ID you choose, and you must be sure the DHCP server will accept it.


SYSTEM MECHANIC - HELP FILE


Maximum Transfer Unit (MTU)

MTU is the default "packet size" (amount of data) that Windows uses to send and receive information over the Internet or your network. When your computer establishes a connection with another, whether via the Internet or LAN, the two computers must use a common MTU value to send and receive data. The computer with the lowest MTU value determines the value that both must use. If the MTU value that is used is larger than that used by any network routers between the computers, these routers must split the data packets into chunks that they can handle, thus causing network "fragmentation". This type of data fragmentation can actually double the amount of time it takes to send a single packet of information. It can dramatically increase performance to set Window’s MTU manually. Windows 95, Windows 98, and Windows Me provide the ability to globally set the MTU value for all network adapters (including NIC’s and Dial up adapters). Windows NT, 2000, XP, and later: NT-based Windows systems allow you to selectively set the MTU for installed network adapters.

Tcp Receive Window Size

Tcp Receive Window size, or "RWIN", is the amount of data (in bytes) that can be received before the sender must await confirmation that the data arrived properly. Another element that is directly relevant to this situation is the Maximum Segment Size or MSS, which is the maximum amount of data that may be received in one network segment at one time, which is calculated as the MTU value minus 40 (40 bytes are allocated for basic TCP and IP information in each segment). Setting the Tcp receive window size to even increments of the MSS increases the percentage of full-sized data segments utilized during transmission, which translates into more efficient downloading, uploading, or other network-based data transfers.

Default Time to Live

Default time to live, or "TTL", is a piece of information included with each segment of data that is transmitted which indicates how long the data should be allowed to "survive" before being discarded. TTL is essentially based on the number of "hops" (or network server transitions) that the data segment can travel over before it considers itself a transmission failure. The larger the TTL value, the greater the chance that data will eventually arrive at it’s destination, however a value too large may also result in unnecessary delays when data is destined to fail due to network errors.

Blackhole detection

A blackhole, in relation to the Internet, is a situation where the your system attempts to automatically determine the MTU of a system on the other end, and is unable to do so because the system on the other end is not able to respond to MTU requests with the proper information. If blackhole detection is enabled, your system uses methods to discover whether connected systems support automatic MTU discovery. If they don’t, the MTU will be detected using alternate and less efficient methods, causing performance degradation.

Automatic MTU detection

Enabling this setting causes your system to attempt to discover the MTU over the path to a remote host. By discovering the remote host’s MTU and limiting TCP segments to this size, TCP can automatically eliminate fragmentation at routers along the path that connect networks with different MTUs. As outlined above, fragmentation adversely affects TCP throughput and network congestion.

Support for TCP large windows

Windows 98 and later provide for the acceptance of larger amounts of data before acknowledgement of receipt is required, which can enhance performance for higher speed connections for networks that have large bandwidth delay products such as high-speed trans-continental connections or satellite links.

Fast retransmission and recovery support

Windows 98 and later support "Fast Retransmission and Fast Recovery of TCP connections" that are encountering IP packet loss in the network. These mechanisms allow a sender to quickly infer a single packet loss by reception of duplicate acknowledgements for a previously sent and acknowledged network packet. This mechanism is useful when the network or Internet is intermittently congested. The reception of 3 (which is the default value) successive duplicate acknowledgements indicates to the sender that it can re-send the last unacknowledged packet (fast retransmit) and not go into "slow start" due to a single packet loss (fast recovery).

Support for Selective Acknowledgements

Windows 98 and later support what are called "Selective Acknowledgements" or "SACK". Selective acknowledgements allow the TCP network to recover from IP packet loss without re-sending packets that were already received by the receiver. Selective Acknowledgements is most useful when employed with TCP large windows.

Number of Allowed Simultaneous HTTP Connections

According to standard HTTP protocol, browsers are not supposed to have more than two connections established to a single web site at one time. Using this option you can override this restriction and instruct Windows to allow Internet Explorer to establish up to ten connections to a single web server at one time, drastically improving performance. This option is divided into two groups: HTTP 1.0 server connections and HTTP 1.1 server connections. To adjust these settings, check the box labeled "Specify Number of Allowed Simultaneous HTTP Connections and drag the corresponding slider controls to increase or decrease the number of allowed simultaneous HTTP connections for the corresponding server type.


TWEAK master - HELP FILE


Maximum Transmission Unit (MTU)

Maximum Transmission Unit. Greatest amount of data that can be transferred in one physical frame on the network. If an IP packet has a larger MTU than the network's frame length, fragmentation will occur. This fragmentation can double the amount of time it takes to send a single packet. MTU is configured independently for each network interface. Please select the network interface you want to optimize from the drop-down list before changing the MTU setting. You can select from the list of predefined settings, or specify a custom value. Click on the MTU Probe button and Tweakmaster will attempt to find the optimal MTU to any given Internet location automatically. Please note that MTU Probe will always identify the smallest setting in the path, so if you have run the wizard the first time through with Optimization Strategy #1 and rebooted, that will set your MTU to the recommended setting of 576 for a dialup connection, and the MTU Probe will always identify the MTU to any Internet location at 576 or smaller. Also note that even if MTU Probe identifies the MTU to a given location as 1500, you still may experience faster throughput using a lower setting due to packet loss and the need for retransmission of data packets. In a nutshell, small packets can be retransmitted more quickly than large ones. Experimentation is the only way to determine this.

MSS

Maximum Segment Size (MSS) defines the largest segment of data that the TCP stack is prepared to receive. When a connection is established, the two ends agree to use the smaller of each end's value. Because headers are typically 40 bytes (20 bytes IP and 20 bytes TCP), MSS is generally 40 bytes less than the MTU.

TCP Receive Window

You can specify the TCP Receive Window size manually, or set it to an even multiple of MSS (e.g. 2x, 4x, 8x) which is invariably recommended for best efficiency. In general, larger receive windows improve performance over high latency, high bandwidth networks.

Max. connections per server

To abide by the HTTP specifications, Windows limits the number of simultaneous connections that it will make to a single HTTP (web) server. This affects all Windows Internet applications that use the standard API, including Internet Explorer. The behavior can be seen when downloading multiple files from a web site only a certain number (2 or 4) will be active at any one time. By default Windows will limit connections to a single HTTP 1.0 server to 4 simultaneous connections. Connections to a single HTTP 1.1 server will be limited to 2 simultaneous connections. The HTTP 1.1 specification (RFC2068) mandates the two connection limit while the four connection limit for HTTP 1.0 is a self-imposed restriction by Internet Explorer. Raise this limit to a higher number, in order to enable simultaneous downloads from the same web site and to make web page rendering in Internet Explorer smoother and faster.

TCP Receive Window

TCP Receive Window (or simply RWIN) determines how much data the receiving computer is prepared to get. After sending the amount of data specified by this setting on the receiving computer, the sending computer will wait for an acknowledgement before sending more. A value that's too large will result in greater loss of data if packets are lost or damaged, and a value that's too small will slow down data transfer considerably, as each packet will have to be acknowledged before the next packet is sent.

Time To Live

Time To Live (TTL): determines the maximum amount of time an IP packet may live in the network without reaching its destination. It is effectively a boundary on the number of routers an IP packet may pass through before being discarded. Due to the expansion of Internet, the recommended setting for this parameter is now 128. Contrary to certain misrepresentations that exist on this matter, there is no value in setting TTL higher than 128.

Session Keep Alive

The parameter controls how often TCP attempts to verify that an idle connection is still intact by sending a keep alive packet. If the remote system is still reachable and functioning, it will acknowledge the keep alive transmission. Keep alive packets are not sent by default. This feature may be enabled on a connection by an application.

Selective Acknowledgement

Selective Acknowledgement (SACK) is an optimizing feature that lets you acknowledge receipt of individual blocks of data in a continuous sequence, rather than just the last sequence number. The recipient can tell the sender that one or more data blocks are missing from the middle of a sequence, and the sender can retransmit only the missing data. SACK is specified in RFC 2018. SACK is enabled by default in Windows.

Path MTU Discovery

When this feature is enabled, TCP will attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote machine. By discovering the Path MTU and limiting TCP segments to this size, TCP can eliminate fragmentation at routers along the path which connect networks with different MTUs. Path MTU Discovery is specified in RFC 1191. Path MTU Discovery is enabled by default in Windows.

"Black Hole" routers detection

When enabled, causes TCP to try to detect "Black Hole" routers while doing Path MTU Discovery. A "Black Hole" router does not return ICMP Destination Unreachable messages when it needs to fragment a TCP packet with the Don't Fragment bit set. TCP depends on receiving these messages to perform Path MTU Discovery. With this feature enabled, TCP will try to send segments without the Don't Fragment bit set if several retransmissions of a segment go unacknowledged. If the segment is acknowledged as a result, the MSS will be decreased and the Don't Fragment bit will be set in future packets on the connection. Enabling black hole detection increases the maximum number of retransmissions performed for a given segment. Black hole detection is disabled by default in Windows.

RFC 1323 Timestamps

Timestamps help TCP to measuring round trip time (RTT) accurately in order to adjust retransmission timeouts. The Timestamps option provides two four-byte timestamp fields in the TCP header, one to record the time the initial transmission is sent and one to record the time on the remote host. Since this option increases packed header overhead and don't provide much of an improvement, it's better left disabled. This option is specified in RFC 1323. Timestamps are disabled by default in Windows.

RFC 1323 Window Scaling

Window scaling permits TCP to negotiate a scaling factor for the TCP receive window size, allowing for a very large TCP receive window of up to 1 GB. This option must be enabled if you want to use receive windows larger than 64 KB. Window scaling is enabled by default in Windows.


INTERNET TURBO - HELP FILE


MTU (Maximum Transmission Unit)

This is the default packet size that Windows uses to negotiate with. When a connection is opened between two computers, they must agree on an MTU. It’s done by comparing MTUs and selecting the smaller of the two. If the MTU is set too large for routers that are between the computers, these routers then fragment this information into a packet size that the router can handle. This fragmentation can double the amount of time it takes to send a single packet. Windows has a built-in MTU Discovery that will adjust for this by sending out a packet that is marked as "Not Fragmental". Then the router sends back an error to the computer saying that the packet was too large, and Windows then lowers the MTU until there are no more errors. If your ISP uses an MTU of 576, then every time you start a connection, Windows must adjust down to this value. Even though Windows automatically adjusts the packet size, it still takes it time to negotiate an acceptable MTU. By setting this value manually, you greatly reduce the amount of work that Windows must do to negotiate.

RWIN (Receive Window)

The TCP Receive Window size is the amount of receive data (in bytes) that can be buffered at one time on a connection. The sending host can send only that amount of data before waiting for an acknowledgment and window update from the receiving host. Matching the receive window to even increments of the MSS increases the percentage of full-sized TCP segments utilized during bulk data transmission. MSS is the MaxMTU - 40 bytes for TCP and IP headers. The RWIN default is 8192 bytes rounded up to the nearest MSS increment for the connection. If that isn't at least 4 times the MSS, then it's adjusted to 4 * MSS, with a maximum size of 64K. With the Windows 95 default MaxMTU of 1500, the default RWIN is rounded up to 8760 (1460 * 6). You can greatly improve performance by setting this to a lower value such as 4 times your MSS (MTU-40). The idea is to bring it to a value below 8192. Many people have better success with 6, 8 or even 10* MSS. In some cases, however, manually setting RWIN may decrease performance because it takes the control away from windows, and if the MTU is negotiated to a different value, then the size of the RWIN is no longer an whole integer multiple. For this to be effective you must make sure your MTU is set where it will not renegotiated to a lower value.

TTL (Time To Live)

TTL is a field in the IP header which indicates how long a packet should be allowed to survive before it is discarded. This value specifies the maximum number of routers that a packet may be forwarded through on to its destination. TTL essentially determines the maximum number of hops permitted. Windows 95 default is 32, but with the Internet growing larger all the time, we recommend to set it to the larger setting of 128.

Session Keep Alive

Specifies how often to send session keepalive packets on active sessions. This will keep connections that have stalled during a particular download session from timing out. Windows default value is 60 minutes, we recommend to set it to 10 minutes.

NDI Cache

NDI Cache is the size of the cache used to store source routing paths. It has a very large effect on the performance of your TCP connection. If your MaxMTU is set to 576 or below, it’s recommended to set the NDI Cache to 16. If your MaxMTU value is greater than 576 set your NDI Cache to 32.

Path MTU Auto Discovery

Enabling this setting causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP is supposed to be able to eliminate fragmentation at routers along the path that connect networks with different MTUs. This requires implementation of the corresponding server side algorithm, however, and presupposes all of the servers on the entire Internet only running MSFT server software with server-side optimization features accessible from MSFT web-browser client software. Needless to say, this is rather unlikely. Nevertheless, it is not recommended to disable this setting as it would then cause an MTU of 576 bytes to be used for all connections that are not to machines on the local subnet. Disabling this setting can cause severe performance degradation because fragmentation may not be compensated for. PMTU Auto Discovery is Enabled by Default.

Black Hole Routers Detect

This specifies whether the stack will attempt to detect Maximum Transmission Unit (MTU) routers that do not send back ICMP fragmentation-needed messages. ICMP (Internet Control Message Protocol) is defined in STD5, RFC 792. With this feature enabled, TCP will try to send segments without the Don't Fragment bit set if several re-transmissions of a segment go unacknowledged. If the segment is acknowledged as a result, the MTU will be decreased and the Don't Fragment bit will be set in future packets on the connection. Enabling black hole detection increases the maximum number of re-transmissions performed for a given segment. Setting this parameter when it is not needed can cause performance degradation. However, if the router is not sending back the ICMP messages, then PMTU Discovery will not work. This can cause an even greater loss of performance. PMTU Black Hole Detect is disabled by default.

MSCPS using HTTP 1.0 & MSCPS using HTTP 1.0

Windows limits connections to a single HTTP 1.0 server to four simultaneous connections. Connections to a single HTTP 1.1 server will be limited to two simultaneous connections. The HTTP 1.1 specification (RFC2068) mandates the two connection limit while the four connection limit for HTTP 1.0 is a self-imposed restriction which coincides with the standard used by a number of popular Web browsers. Use this option in order to increase the number of simultaneous downloads from the same web site.


SPEED TEC - HELP FILE


Auto Discovery

Enabling Auto Discovery causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP is supposed to be able to eliminate fragmentation at routers along the path that connect networks with different MTUs. This requires implementation of the corresponding server side algorithm, however, and presupposes all of the servers on the entire Internet only running MSFT server software with server-side optimization features accessible from MSFT web-browser client software. Needless to say, this is rather unlikely. Nevertheless, it is not recommended to disable this setting as it would then cause an MTU of 576 bytes to be used for all connections that are not to machines on the local subnet. Disabling this setting can cause severe performance degradation because fragmentation may not be compensated for. PMTU Auto Discovery is Enabled by Default.

Black Hole Detect

This specifies whether the Windows TCP/IP stack will attempt to detect Maximum Transmission Unit (MTU) routers that do not send back ICMP fragmentation-needed messages. ICMP (Internet Control Message Protocol) is defined in STD5, RFC 792. With this feature enabled, TCP will try to send segments without the Don't Fragment bit set if several re-transmissions of a segment go unacknowledged. If the segment is acknowledged as a result, the MTU will be decreased and the Don't Fragment bit will be set in future packets on the connection. Enabling black hole detection increases the maximum number of re-transmissions performed for a given segment. Setting this parameter when it is not needed can cause performance degradation. However, if the router is not sending back the ICMP messages, then PMTU Discovery will not work. This can cause an even greater loss of performance. PMTU Black Hole Detect is disabled by default. Error message: "Unexpected Runtime Error 50003" This error is caused by the wrong version of the Microsoft Runtime files installed on your machine. They were likely installed by another program, as SpeedTec uses the latest versions. For information on how to correct this problem, click here.

MTU

All data sent over the Internet goes in data packets. The size of these data packets is called the Maximum Transmission Unit (MTU). If these data packet sizes are too large, they will have to be broken apart (fragmented) to squeeze through some of the routers on the Internet, then re-assembled on the other side of those routers. That causes delay in data transmission. If the data packet sizes are too small, that will also slow things down.

RWIN

Information sent over the Internet goes in data packets. Think of data packets as letters sent through the mail. MaxMTU is the size of the entire envelope, including the letter inside. The Default Receive Window (RWin) is the size of the batch of letters being received at one time. You want RWin to be an even multiple of the Maximum Segment Size (MSS). MSS equals the size of the MaxMTU, minus 40 bytes for header data. Think of MSS as the letter inside the envelope (MSS = MaxMTU - 40). If RWin isn't set to an even multiple of MSS, you'll have fragmentation of the last data packet in that batch.

TTL

When you send data packets over the Internet, it goes through many routers along the way. The Time to Live setting determines how many routers your packet can go through before it is discarded.

Session Keep Alive

Sometimes when you try to download a file, it will get stalled over the Internet; perhaps because of an overloaded router along the way. The Session Keep Alive setting determines how long your computer will wait while receiving no data from the server out on the Internet.

NDI Cache

This is a controversial setting. Some people have reported good results from setting this to 16, some have reported no changes at all. It is included in this program for your experimentation.

Host

Each web site on the Internet has a plain-English domain name (www.yahoo.com) and a Numerical IP address (204.71.200.67). Your computer needs the numerical IP address to go to the web site. When you type "www.yahoo.com" into your browser, your computer gets the IP number from special computers on the Internet. These special computers are called Domain Name Servers (DNS). Domain Name Servers maintain huge lists of domain names and their corresponding IP addresses. I take your computer several seconds to go to the DNS and get the IP address. SpeedTec's Hosts file editor stores IP Numbers of your favorite web sites on your hard drive (the file is C:\Windows\Hosts). When you visit one of those sites, your browser will get the IP address from the local file, which will be several seconds faster than getting it from the Internet.


NET ACCELERATOR - HELP FILE


MTU (Maximum Transmission Unit)

This is the default packet size that Windows uses to negotiate with. When a connection is opened between two computers, they must agree on an MTU. It’s done by comparing MTU and selecting the smaller of the two. If the MTU is set too large for routers that are between the computers, these routers then fragment this information into a packet size that the router can handle. This fragmentation can double the amount of time it takes to send a single packet. Windows has a built-in MTU Discovery that will adjust for this by sending out a packet that is marked as "Not Fragmental". Then the router sends back an error to the computer saying that the packet was too large, and Windows then lowers the MTU until there are no more errors. If your ISP uses an MTU of 576, then every time you start a connection, Windows must adjust down to this value. Even though Windows automatically adjusts the packet size, it still takes it time to negotiate an acceptable MTU. By setting this value manually, you greatly reduce the amount of work that Windows must do to negotiate.

RWIN (Receive Window)

This is the default packet size that Windows uses to negotiate with. When a connection is opened between two computers, they must agree on an MTU. It’s done by comparing MTU and selecting the smaller of the two. If the MTU is set too large for routers that are between the computers, these routers then fragment this information into a packet size that the router can handle. This fragmentation can double the amount of time it takes to send a single packet. Windows has a built-in MTU Discovery that will adjust for this by sending out a packet that is marked as "Not Fragmental". Then the router sends back an error to the computer saying that the packet was too large, and Windows then lowers the MTU until there are no more errors. If your ISP uses an MTU of 576, then every time you start a connection, Windows must adjust down to this value. Even though Windows automatically adjusts the packet size, it still takes it time to negotiate an acceptable MTU. By setting this value manually, you greatly reduce the amount of work that Windows must do to negotiate.

TTL (Time To Live)

TTL is a field in the IP header which indicates how long a packet should be allowed to survive before it is discarded. This value specifies the maximum number of routers that a packet may be forwarded through on to its destination. TTL essentially determines the maximum number of hops permitted. Windows 95 default is 32, but with the Internet growing larger all the time, we recommend to set it to the larger setting of 128.

MTU Auto Discovery

Enabling this setting causes TCP to attempt to discover the Maximum Transmission Unit (MTU or largest packet size) over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP is supposed to be able to eliminate fragmentation at routers along the path that connect networks with different MTUs. This requires implementation of the corresponding server side algorithm, however, and presupposes all of the servers on the entire Internet only running MSFT server software with server-side optimization features accessible from MSFT web-browser client software. Needless to say, this is rather unlikely. Nevertheless, it is not recommended to disable this setting as it would then cause an MTU of 576 bytes to be used for all connections that are not to machines on the local subnet. Disabling this setting can cause severe performance degradation because fragmentation may not be compensated for. MTU Auto Discover is Enabled by Default.

Black Hole Detection

Black Hole Detection specifies whether the stack will attempt to detect Maximum Transmission Unit routers that do not send back ICMP fragmentation-needed messages. Enabling black hole detection increases the maximum number of re-transmissions performed for a given segment. Setting this parameter 'enabled', when it is not needed, can cause performance degradation. If the router is not sending back the ICMP messages, then PMTU will not work. This can cause an even greater loss of performance. It is recommended that PMTU Black Hole Detect be disabled. Black Hole Detect is disabled by default.

Session Keep Alive

Specifies how often to send session keep alive packets on active sessions. This will keep connections that have stalled during a particular download session from timing out. Windows default value is 60 minutes, we recommend to set it to 10 minutes.

NDI Cache

NDI Cache is the size of the cache used to store source routing paths. It has a very large effect on the performance of your TCP connection. If your MAXMTU is set to 576 or below, it’s recommended to set the NDI Cache to 16. If your MAXMTU value is greater than 576 set your NDI Cache to 32.

Maximum Sessions Allowed

Windows limits connections to a single HTTP 1.0 server to four simultaneous connections. Connections to a single HTTP 1.1 server will be limited to two simultaneous connections. The HTTP 1.1 specification (RFC2068) mandates the two connection limit while the four connection limit for HTTP 1.0 is a self-imposed restriction which coincides with the standard used by a number of popular Web browsers. Use this option in order to increase the number of simultaneous downloads from the same web site.