DECmate was the name of a series of PDP-8 -compatible computers produced by the Digital Equipment Corporation in the late 1970s and early 1980s. All of the models used an Intersil 6100 (later known as the Harris 6100) or Harris 6120 (an improved Intersil 6100) microprocessor which emulated the 12-bit DEC PDP-8 CPU. They were text-only and used the OS/78 or OS/278 operating systems , which were extensions of OS/8 for the PDP-8. Aimed at the word processing market, they typically ran the WPS-8 word-processing program. Later models optionally had Intel 8080 or Z80 microprocessors which allowed them to run CP/M . The range was a development of the VT78 which was introduced in July 1977.
57-448: Introduced in July 1977, this machine was built into a VT52 case and had an Intersil 6100 microprocessor running at 2.2 MHz. The standard configuration included an RX02 dual 8-inch floppy disk unit which was housed in the pedestal that the computer rested on. Introduced in 1980, this machine was built into a VT100 case. It had a 10 MHz clock and 32 Kwords of memory. It
114-411: A VT52-based screen driver in an era when ANSI escape codes had already become almost universal. This version added several new commands including the ability to select colors. VT52 commands normally consisted of the escape character and a single character following it. The exception to this rule was the Y command, which also required two numbers to be sent. The ESC Y code was used to position
171-461: A choice of two boards with both a Z80 and an Intel 8086 , the difference being that they had either 256 KB or 512 KB RAM. Manufacture ceased in 1986. It was superseded by the DECmate III, introduced in 1984. This was introduced in 1984. It had a smaller system case, color monitor, 8 MHz clock, two 5.25-inch RX50 floppy disk drives, 32 KB user RAM, 32 KB system RAM. It
228-442: A digital communication channel is the capacity excluding the physical layer protocol overhead, for example time division multiplex (TDM) framing bits , redundant forward error correction (FEC) codes, equalizer training symbols and other channel coding . Error-correcting codes are common especially in wireless communication systems, broadband modem standards and modern copper-based high-speed LANs. The physical layer net bitrate
285-472: A format sometimes abbreviated like "16bit / 44.1kHz". CD-DA is also stereo , using a left and right channel , so the amount of audio data per second is double that of mono, where only a single channel is used. The bit rate of PCM audio data can be calculated with the following formula: For example, the bit rate of a CD-DA recording (44.1 kHz sampling rate, 16 bits per sample and two channels) can be calculated as follows: The cumulative size of
342-614: A length of PCM audio data (excluding a file header or other metadata ) can be calculated using the following formula: The cumulative size in bytes can be found by dividing the file size in bits by the number of bits in a byte, which is eight: Therefore, 80 minutes (4,800 seconds) of CD-DA data requires 846,720,000 bytes of storage: where MiB is mebibytes with binary prefix Mi, meaning 2 = 1,048,576. The MP3 audio format provides lossy data compression . Audio quality improves with increasing bitrate: For technical reasons (hardware/software protocols, overheads, encoding schemes, etc.)
399-439: A loop had to be nearly constant, or text lower on the screen would be displayed in the wrong place during that refresh. Typing a character produced a noise by activating a relay. The relay was also used as a buzzer to sound the bell character , producing a sound that "has been compared to the sound of a '52 Chevy stripping its gears." DEC also offered an optional hard-copy device called an electrolytic copier, which fit into
456-463: A thin helical bar wrapped around a rotating drum. One rotation of the drum scanned an intersecting area of the electrodes across the width of the paper. While the copier did an admirable job of capturing the contents of the screen, the output of the copier had an unfortunate resemblance to wet toilet tissue . Digital patented the innovation of having a single character generator provide the text font for both screen and copier. The basic layout of
513-568: A variant of Digital's OS/8 operating system, and usually WPS-8 , Digital's word processing system. VT52 codes remained proprietary to DEC, although a number of other companies provided emulations in their terminals. Later VT series terminals supported a subset of these commands. One interesting case is the GEMDOS system and its offshoot, the TOS operating system of the Atari ST . These systems used
570-453: Is 125 Mbit/s, due to the 4B5B (four bit over five bit) encoding. In this case, the gross bit rate is equal to the symbol rate or pulse rate of 125 megabaud, due to the NRZI line code . In communications technologies without forward error correction and other physical layer protocol overhead, there is no distinction between gross bit rate and physical layer net bit rate. For example,
627-469: Is a CRT -based computer terminal that was introduced by Digital Equipment Corporation (DEC) in July 1974. It provided a display with 12 rows and 80 columns of upper-case text, and used an expanded set of control characters and forward-only scrolling based on the earlier VT05 . DEC documentation of the era refers to the terminals as the DECscope , a name that was otherwise almost never seen. The VT50
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#1732794510216684-804: Is not the case for modern modulation systems used in modems and LAN equipment. For most line codes and modulation methods: More specifically, a line code (or baseband transmission scheme) representing the data using pulse-amplitude modulation with 2 N {\displaystyle 2^{N}} different voltage levels, can transfer N {\displaystyle N} bits per pulse. A digital modulation method (or passband transmission scheme) using 2 N {\displaystyle 2^{N}} different symbols, for example 2 N {\displaystyle 2^{N}} amplitudes, phases or frequencies, can transfer N {\displaystyle N} bits per symbol. This results in: An exception from
741-408: Is possible without bit errors for a certain physical analog node-to-node communication link . The channel capacity is proportional to the analog bandwidth in hertz. This proportionality is called Hartley's law . Consequently, the net bit rate is sometimes called digital bandwidth capacity in bit/s. The term throughput , essentially the same thing as digital bandwidth consumption , denotes
798-437: Is provided by the network equipment or protocols, we have the following relation: for a certain communication path. These are examples of physical layer net bit rates in proposed communication standard interfaces and devices: In digital multimedia, bit rate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors: Generally, choices are made about
855-405: Is the datarate measured at a reference point in the interface between the data link layer and physical layer, and may consequently include data link and higher layer overhead. In modems and wireless systems, link adaptation (automatic adaptation of the data rate and the modulation and/or error coding scheme to the signal quality) is often applied. In that context, the term peak bitrate denotes
912-583: Is used to mean one million bits per second. In most computing and digital communication environments, one byte per second (symbol: B/s ) corresponds to 8 bit/s. When quantifying large or small bit rates, SI prefixes (also known as metric prefixes or decimal prefixes) are used, thus: Binary prefixes are sometimes used for bit rates. The International Standard ( IEC 80000-13 ) specifies different symbols for binary and decimal (SI) prefixes (e.g., 1 KiB /s = 1024 B/s = 8192 bit/s, and 1 MiB /s = 1024 KiB/s). In digital communication systems,
969-410: The physical layer gross bitrate , raw bitrate , data signaling rate , gross data transfer rate or uncoded transmission rate (sometimes written as a variable R b or f b ) is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead. In case of serial communications , the gross bit rate is related to
1026-416: The source information rate , also known as the entropy rate . The bitrates in this section are approximately the minimum that the average listener in a typical listening or viewing environment, when using the best available compression, would perceive as not significantly worse than the reference standard. Compact Disc Digital Audio (CD-DA) uses 44,100 samples per second, each with a bit depth of 16,
1083-558: The DECmate series over the IBM PC systems. The I/O interfaces worked slightly differently, which meant that most existing user and system programs could not detect Control-C and exit reliably. Every program, both user and system, had to be patched to fix this anomaly. Additionally, the CPU and screen update speeds were noticeably slower than the older PDP-8 systems. VT52 The VT50
1140-487: The VT50 did not support lowercase letters. Computer users of that era seldom needed lowercase text. The VT50H added a separate "auxilary keyboard" on the right side of the original keyboard. This was arranged in the fashion of a numeric keypad with additional control keys above the numbers. Four of these were cursor keys which sent ESC A through D for up, down, left and right, respectively. Another three of
1197-443: The above factors in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played. If lossy data compression is used on audio or visual data, differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifacts . Whether these affect
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#17327945102161254-694: The above is some self-synchronizing line codes, for example Manchester coding and return-to-zero (RTZ) coding, where each bit is represented by two pulses (signal states), resulting in: A theoretical upper bound for the symbol rate in baud, symbols/s or pulses/s for a certain spectral bandwidth in hertz is given by the Nyquist law : In practice this upper bound can only be approached for line coding schemes and for so-called vestigial sideband digital modulation. Most other digital carrier-modulated schemes, for example ASK , PSK , QAM and OFDM , can be characterized as double sideband modulation, resulting in
1311-400: The achieved average useful bit rate in a computer network over a logical or physical communication link or through a network node, typically measured at a reference point above the data link layer. This implies that the throughput often excludes data link layer protocol overhead. The throughput is affected by the traffic load from the data source in question, as well as from other sources sharing
1368-462: The bit transmission time T b {\displaystyle T_{\text{b}}} as: The gross bit rate is related to the symbol rate or modulation rate, which is expressed in bauds or symbols per second. However, the gross bit rate and the baud value are equal only when there are only two levels per symbol, representing 0 and 1, meaning that each symbol of a data transmission system carries exactly one bit of data; for example, this
1425-401: The blank panel on the right side of the display. This device was able to print, scan-line by scan-line, an exact replica of the screen onto a damp roll of special paper. It did this by electroplating metal from an electrode into the paper. The paper ran between two electrodes. The electrode on one side was a thin straight bar oriented across the paper width. The electrode on the other side was
1482-501: The connection establishment phase due to adaptive modulation – slower but more robust modulation schemes are chosen in case of poor signal-to-noise ratio . Due to data compression, the actual data transmission rate or throughput (see below) may be higher. The channel capacity , also known as the Shannon capacity, is a theoretical upper bound for the maximum net bitrate, exclusive of forward error correction coding, that
1539-483: The cursor anywhere on the screen, using two parameters representing the X and Y coordinates of the cursor position, with the upper left corner of the screen being position 1,1. These numbers were sent as ASCII characters of that value, adding 31. For instance, to position the cursor at column 30 and line 20, you would add 31 to each value to get 61 and 51, then look up those ASCII characters, = and 3 . The complete command would then be ESC Y 3 = (note
1596-399: The data while the display hardware was inactive between raster scan lines, and then triggered the display hardware to take over at the appropriate time. The display system returned control to the CPU when it completed drawing the line. The CPU was so basic that addition and subtraction could only be done by repeatedly incrementing or decrementing two registers. Moreover, the time taken by such
1653-399: The encoding bit rate is the goodput that is required to avoid playback interruption. The term average bitrate is used in case of variable bitrate multimedia source coding schemes. In this context, the peak bit rate is the maximum number of bits required for any short-term block of compressed data. A theoretical lower bound for the encoding bit rate for lossless data compression is
1710-446: The file size (in bytes) divided by the file transfer time (in seconds) and multiplied by eight. As an example, the goodput or data transfer rate of a V.92 voiceband modem is affected by the modem physical layer and data link layer protocols. It is sometimes higher than the physical layer data rate due to V.44 data compression , and sometimes lower due to bit-errors and automatic repeat request retransmissions. If no data compression
1767-534: The following relation: In case of parallel communication , the gross bit rate is given by where n is the number of parallel channels, M i is the number of symbols or levels of the modulation in the i th channel , and T i is the symbol duration time , expressed in seconds, for the i th channel. The physical layer net bitrate , information rate , useful bit rate , payload rate , net data transfer rate , coded transmission rate , effective data rate or wire speed (informal language) of
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1824-482: The gross bit rate and net bit rate is affected by the FEC code rate according to the following. The connection speed of a technology that involves forward error correction typically refers to the physical layer net bit rate in accordance with the above definition. For example, the net bitrate (and thus the "connection speed") of an IEEE 802.11a wireless network is the net bit rate of between 6 and 54 Mbit/s, while
1881-472: The gross bit rate is between 12 and 72 Mbit/s inclusive of error-correcting codes. The net bit rate of ISDN2 Basic Rate Interface (2 B-channels + 1 D-channel) of 64+64+16 = 144 kbit/s also refers to the payload data rates, while the D channel signalling rate is 16 kbit/s. The net bit rate of the Ethernet 100BASE-TX physical layer standard is 100 Mbit/s, while the gross bitrate
1938-410: The keys on the keyboard sent a command sequence back to the host computer. The VT55 incorporated an add-on graphics system that was capable of displaying two mathematical functions or histograms . This was invoked by sending a command string that sent the terminal into graphics mode , with further data being sent to a separate buffer and CPU. Both systems mixed their data during the display, allowing
1995-411: The keys were unlabeled and could be programmed to return any two-character code, and would default to ESC P through R . The VT50 was soon replaced by the greatly upgraded VT52. The VT52 had considerably larger buffers, giving it the capacity to store not only a full 24 lines of text that better utilized the screen space, but also the text off the top and bottom of the screen. This allowed
2052-456: The lower case characters and some punctuation with new characters useful for the display of math. Unusual were glyphs for ¹⁄, ³⁄, ⁵⁄, ⁷⁄, which could be combined with subscript numbers to produce things like ⅗, and scan lines allowing a function to be plotted with 8 times higher vertical resolution than text. Later VT terminals supported VT52 commands, as well as adding a single new command to return to full ANSI mode. Compatibility mode changed
2109-476: The machine booted. It was also known as the PC278. The model could be expanded, either by adding another pair of 5.25-inch floppy disk drives, and it could also support either an additional pair of RX01 or RX02 8-inch floppy disk drives or a Winchester disk . It can also have a coprocessor board added, to allow it to run CP/M . There was a choice of three coprocessor boards, one with a Z80 and 64 KB RAM, and
2166-441: The much more sophisticated VT100 in 1978. These terminals supported asynchronous communication at baud rates up to 9600 bits per second and did not require any fill characters . Like other early DEC terminals they were equipped with both an RS-232 port as well as a 20mA current loop , an older serial standard used with teletype machines that was more suitable for transmission over long runs of twisted-pair wiring. Data
2223-520: The net as well as gross bit rate of Ethernet 10BASE-T is 10 Mbit/s. Due to the Manchester line code, each bit is represented by two pulses, resulting in a pulse rate of 20 megabaud. The "connection speed" of a V.92 voiceband modem typically refers to the gross bit rate, since there is no additional error-correction code. It can be up to 56,000 bit/s downstream and 48,000 bit/s upstream . A lower bit rate may be chosen during
2280-465: The net bitrate of the fastest and least robust transmission mode, used for example when the distance is very short between sender and transmitter. Some operating systems and network equipment may detect the " connection speed " (informal language) of a network access technology or communication device, implying the current net bit rate. The term line rate in some textbooks is defined as gross bit rate, in others as net bit rate. The relationship between
2337-423: The others it had a monochrome VR201 ( VT220 -style) monitor, an LK201 keyboard and dual 400 KB single-sided quad-density 5.25-inch RX50 floppy disk drives. It had 32 Kwords of RAM for use by programs, and a further 32 Kwords containing code which was used for device emulation. Code running in this second bank was nicknamed "slushware", in contrast to firmware since it was loaded from floppy disk as
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2394-433: The perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener's perceptions, the listener's familiarity with artifacts, and the listening or viewing environment. The encoding bit rate of a multimedia file is its size in bytes divided by the playback time of the recording (in seconds), multiplied by eight. For real-time streaming multimedia ,
2451-449: The rear, were cooled by convection . The large, flat top of the terminal frequently accommodated large volumes of DEC documentation, which could block the vents and cause overheating. The VT50 was the first terminal Digital produced in this cabinet. It provided only 12 lines of text with blank lines between them to use the entire vertical area of the display. Like its predecessor, the VT05 ,
2508-673: The response to the ESC Z command; all models responded with the code ESC / Z . The GEMDOS version of the VT52 command set adds a number of new commands. These mostly concerned color support, with the color selection being sent as a single character using the same number-to-character encoding as the Y command. Only the last four bits of the number were used, providing support for 16 colors. The Atari ST only supported 4 of those in 80 column mode and all 16 in 40 column mode. A few new cursor commands were added as well, essentially filling out
2565-477: The row, column ordering, not X, Y). Adding 31 ensures that the characters are shifted out of the control range into the printable character range, so they will transmit properly. The ESC Z command allowed the host computer to identify the capabilities of the terminal. There were eight possible responses. Several additional codes were used with the optional copier: The VT52 and VT55 included two characters sets, ASCII and "graphics mode" which switched out
2622-400: The same cabinet but had a more complete custom processor. Application-specific behavior was coded in separate PROM memory, using a separate instruction code that the processor interpreted. This unpublished language was to be used to easily develop additional models specific to single Digital marketing organizations. These terminals synthesized a "tock" sound on a speaker for feedback when a key
2679-425: The same network resources. See also measuring network throughput . Goodput or data transfer rate refers to the achieved average net bit rate that is delivered to the application layer , exclusive of all protocol overhead, data packets retransmissions, etc. For example, in the case of file transfer, the goodput corresponds to the achieved file transfer rate . The file transfer rate in bit/s can be calculated as
2736-406: The set of the original VT52 by including commands that cleared toward the top of the screen instead of the bottom. The system did not support a number of VT52 commands, including F, G and Z. Bit rate In telecommunications and computing , bit rate ( bitrate or as a variable R ) is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in
2793-484: The terminal to scroll backwards a limited amount without having to ask the host to re-send data. Another significant upgrade was that the VT52 included lowercase text support. Many new commands and features were added: One notable feature was the introduction of a separate function keypad with the " Gold Key ", which was used for editing programs like WPS-8 , KED, and EDT . Pressing the Gold Key and then typing one of
2850-440: The terminal, with the screen and main keyboard on the left and the blank area on the right, was intended to allow the system to be upgraded. The printer was one such upgrade, but over time DEC offered a number of other options. The large size of the cabinet was deliberate, to avoid a cooling fan. The two circuit boards with processor and memory at the base of the terminal, and a single board with power-supply and monitor electronics at
2907-413: The unit bit per second (symbol: bit/s ), often in conjunction with an SI prefix such as kilo (1 kbit/s = 1,000 bit/s), mega (1 Mbit/s = 1,000 kbit/s), giga (1 Gbit/s = 1,000 Mbit/s) or tera (1 Tbit/s = 1,000 Gbit/s). The non-standard abbreviation bps is often used to replace the standard symbol bit/s, so that, for example, 1 Mbps
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#17327945102162964-493: The user to mix graphics and text on a single screen, as opposed to systems like the Tektronix 4010 or plotters that had to slowly draw text using graphics commands. This system became known as waveform graphics , and would re-appear on the later VT105. The VT61 and VT62 were block-mode terminals . The VT62 was to be used in conjunction with TRAX, a transaction processing operating system on high-end PDP-11 's. They used
3021-540: Was also known as the PC238. This was introduced in 1985 and withdrawn in 1990. It included a hard disk controller as part of the basic configuration. Otherwise, it was very similar to the DECmate III. It was also known as the PC24P. The DECmates were acceptable for word-processing, but due to various hardware quirks, were somewhat incompatible with many existing PDP-8 programs, largely eliminating one potential advantage of
3078-769: Was also known as the VT278. As part of a three-pronged strategy against IBM , the company released this model in 1982 at the same time as the PDP-11 -based PRO-350 and the Intel 8088 -based Rainbow 100 . The DECmate II resembles the Rainbow 100 but uses the 6120 processor. Its two operating systems are the WPS-8 word processing system, and the COS-310 Commercial Operating System running DIBOL . Like
3135-410: Was pressed instead of the relay. Though the keyboards were identical, VT6x users admired the superior "feel". The relatively large expansion area of the VT50 case, combined with rapidly shrinking electronics in the late 1970s, allowed DEC to produce single-box, stand-alone minicomputer /terminals similar to a contemporary microcomputer . The VT78 added a single-chip PDP-8 processor to the VT52, ran
3192-399: Was read into a small buffer, which the display hardware periodically read to produce the display. Characters typed on the keyboard were likewise stored in a buffer and sent over the serial line as quickly as possible. To interpret the commands being sent in the serial data, it used a primitive central processing unit (CPU) built from small-scale-integration integrated circuits . It examined
3249-518: Was sold only for a short period before it was replaced by the VT52 in September 1975. The VT52 provided a screen of 24 rows and 80 columns of text and supported all 95 ASCII characters as well as 32 graphics characters, bi-directional scrolling, and an expanded control character system. DEC produced a series of upgraded VT52's with additional hardware for various uses. The VT52 family was followed by
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