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Input/Output Channels
Electronic Image

Photography (Advanced) - Advanced manual for photography and other graphic techniques
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Data Transmission Methods Data may be transmitted over a channel in one of two ways, either in the serial or the parallel mode. SERIAL  MODE.—In  serial  mode  (transmission), three wires are required: one to transmit data, one to receive data, and one for a ground. The data is sent or received in the form of bits, one alter another in a series, as shown in figure 3-2. This type of transmission is desirable whenever a computer system is linked to outside peripherals over a long distance, such as remote terminals. PARALLEL   MODE.—In   parallel   mode (transmission), the data bits are all sent or received simultaneously. Parallel transmission requires nine or ten  wires  to  connect  the  computer  to  the  peripheral device (fig. 3-2). Seven or eight lines are required for data bits, one or two lines for “handshake” purposes, and  one  line  for  a  ground.  The  handshaking  signals communicate information back and forth between the peripheral devices and the computer. This information lets the peripheral know when the computer is ready to accept another character and vice versa. This type of transmission  is  useful  for  fast  data  transfer.  The principal  drawback  is  the  computer  must  not  be  located relatively close to the peripheral device. MODEMS When data is transmitted directly to the computer over long distances, it is necessary to add two other devices, one at each end. These devices are called modems.   The   word   modem   is   an   acronym   for MOdulator-DEModulator. A modem converts the digital signal produced by a computer to asuitable audio signal for transmission over communication lines (I/O Figure 3-2.—Serial and parallel data transmission. channels). The modem at the other end of the line reconverts the audio signal back to a digital signal before sending it to the CPU. If this conversion (digital to audio) was not carried out, the digital signal would degenerate  during  transmission  and  become  garbled. Modems are commonly used to send and receive data over  telephone  lines,  making  them  a  very  valuable  tool for  imaging  facilities. COMPUTER SYSTEM SOFTWARE Software plays an important role in computer operations.  Without  software,  a  computer  could  not perform simple addition. It is the software that makes everything  happen.  "Software"  may  be  defined  as  all the stored programs and routines (operating aids) required to use the capabilities of a computer system fully.  Basically,  two  types  of  software  are  used: systems software and applications software. SYSTEMS SOFTWARE Systems software is often referred to as systems programs.  Systems  software  consists  of  supervisory and support programs designed to coordinate the capabilities  of  the  computer  itself.  These  include programs, such as operating systems, assemblers and compilers,  and  utilities. Operating Systems An  operating  system  is  a  collection  of  many programs used by the computer to manage resources and operations. These programs control the execution of other programs. They schedule, assign resources, monitor, and control the work of the computer. These actions are carried out without human intervention. Assemblers and Compilers Both  assemblers  and  compilers  are  language translators. They are designed for specific machines and  specific  languages.  They  translate  computer programs  written  in  programming  language  into machine  language.  A  language  translator  for  an assembly  language  is  called  an  assembler  program. Most high-level language translators are compiler programs.  These  translators  are  designed  to  convert artificial   languages   used   by   programmers   into machine-usable  code  after  it  is  entered  into  the computer. 3-6







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