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A block-oriented terminal or block mode terminal is a type of computer terminal that communicates with its host in blocks of data, as opposed to a character-oriented terminal that communicates with its host one character at a time. The IBM 3270 is perhaps the most familiar implementation of a block-oriented terminal, but most mainframe computer manufacturers and several other companies produced them.
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying or printing data from, a computer or a computing system. The teletype was an example of an early day hardcopy terminal, and predated the use of a computer screen by decades.
A network host is a computer or other device connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network address.
A character-oriented terminal is a type of computer terminal that communicates with its host one character at a time, as opposed to a block-oriented terminal that communicates in blocks of data. It is the most common type of data terminal, because it's easy to implement and program. Connection to the mainframe computer or terminal server is achieved via RS-232 serial links, Ethernet or other proprietary protocols.
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In a typical application the host sends the terminal a preformatted panel containing both static data and fields into which data may be entered. The terminal operator keys data, such as updates in a database entry (or the device's buffer - 3270), into the appropriate fields. When entry is complete (or ENTER or PF key pressed on 3270's), a block of data, usually just the data entered by the operator (modified data), is sent to the host in one transmission. The 3270 terminal buffer (at the device) could be updated on a single character basis, if necessary, because of the existence of a "set buffer address order" (SBA), that usually preceded any data to be written/overwritten within the buffer. A complete buffer could also be read or replaced using the READ BUFFER command or WRITE Command (unformatted or formatted in the case of the 3270).
A panel is "a particular arrangement of information grouped together for presentation to users in a window or pop-up". In ISPF, a panel is "a predefined display image that you see on a display screen".
A database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques.
Block-oriented terminals have the advantage of causing less system load on the host and less network traffic than character-oriented terminals. On a multi-drop line there is considerable overhead for each transmission which is the same for a single character as for thousands of characters. Block-oriented terminals may also appear more responsive to the user, especially over slow connections, since editing within a field is done locally on the terminal itself rather than depending on echoing from the host system.
In UNIX computing, the system load is a measure of the amount of computational work that a computer system performs. The load average represents the average system load over a period of time. It conventionally appears in the form of three numbers which represent the system load during the last one-, five-, and fifteen-minute periods.
In telecommunications, echo is the local display of data, either initially as it is locally sourced and sent, or finally as a copy of it is received back from a remote destination. Local echo is where the local sending equipment displays the outgoing sent data. Remote echo is where the display is a return copy of data as received remotely. Both are used together in a computed form of error detection to ensure that data received at the remote destination of a telecommunication are the same as data sent from the local source. When (two) modems communicate in echoplex mode the remote modem echoes whatever it receives from the local modem.
Early terminals had limited editing capabilities – 3270 terminals, for example, only offered the ability to check data entered into a field defined as numeric. [1] Later so-called "smart" or "intelligent" terminals incorporated microprocessors and supported more local processing.
