A binary 0 will be a pulse of phase 180 degrees and will be a low polarity followed by a high polarity. Type D can transmit digital signals up to 1,000 feet. TYPE    E    (NATO    SERIAL).—    Type    E asynchronously transfers serial data of up to 10^-million bits per second on single triaxial cable. Channel control is  similar  to  NTDS  parallel  channels.  This  type interface uses a bipolar plus or minus 0.6 volt nominal (0.8 volt maximum). Type E can transmit digital signals up to 1,000 feet depending on the type of cable used. It is most frequently used in large mainframes to interface  with  external  equipment  found  in  the  data processing    subsystems    (includes    intercomputer communication). Interfacing with an external device uses a normal serial I/O interfacing: enable and request. The  channel  interface  uses  a  SIS/SOS  protocol, transferring control and data words using the following word transfers: external function, output data, external interrupt, and input data. The data (command or data) words are transmitted in serial bursts of up to thirty two 32-bit words (1,024 bits). The burst transmissions are coordinated using Sink Status (SIS) frames or Source Status (SOS) frames. The SIS frame is sent from the receiving device when it is ready to receive a burst. The SOS  frame  is  sent  by  the  transmitting  device  to coordinate and synchronize the burst transmission. TYPE  F  (AIRCRAFT  INTERNAL  TIME DIVISION MULTIPLEX (TDM) BUS).—  Type F transfers serial data up to one million bits per second over  a  distance  of  300  feet.  A  logical  1  will  be transmitted as a bipolar coded signal 1/0 (a positive pulse followed by a negative pulse). A logic zero will be a bipolar coded signal 0/1 (a negative pulse followed by a positive pulse). This type interface transmits bit groupings of 20 bits: data, sync wave form, and parity bit. It is most frequently used in large mainframes to interface with equipment found in the data processing subsystems. Type  F  uses  a  command/response protocol. Transfers include command, data, and status words over a single channel. This interface can handle up to 32 external devices on one channel; one device must be a bus controller. TYPE G (RS-449).—  Type  G  equates  with  the functional   and   procedural   portions   of   RS-232. However, the electrical and mechanical specifications are covered by RS-422. Type G is intended to transfer serial data above 20 kilo bits per second and up to 2 million bits per second over a single cable. Type G can transmit  data  up  to  200  feet.  Signals  are  divided between 37-pin and 9-pin connectors, and the ground and common signals are handled separately for each cable. Type G can send asynchronous serial data up to 9600 bits per second. This type of interface is used to transmit bit groupings of 8, 16, or 32 bits depending on the type of computer. Type G can be used in mainframe and  microcomputers. Type  G  uses  primarily  a command and response protocol. TYPE H (HIGH-SPEED PARALLEL).—  Type H transfers parallel data of up to 500,000 words per second on one cable. This type interface uses 0 vdc (logical 1) and +3.5 vdc (logical 0 to transmit bit groupings of 16, 30, or 32 bits depending on the type of computer. Type H can transmit digital signals up to 300 feet. It is most frequently used in large mainframes to interface with equipment found in the data processing, display, and communication subsystems. Type H uses a  request  and  acknowledge  protocol  process.  It transfers  control  and  data  words  using  two  cables—one input and one output for the same channel. It can also interface with external equipment having a type C interface. You may, however, encounter a few devices that use input only or output only portions of an NTDS slow channel. Type H uses the same input and output signal designations as type A. TYPE J (FIBER OPTIC NATO SERIAL).— Type J is used for the fiberoptic implementation of type E. A type J fiber optic channel converts a type E serial bit stream into light pulses that are carried by a fiber optic cable to a receiving device that converts the light pulses back into a digital bit stream. For further details on fiber optics, refer to NEETS 24,  Introduction  to Fiber Optics. Small Computer System Interface (ANSI X3.131) The small computer system interface (SCSI) uses a digital parallel format. SCSI is pronounced “skuzzy.” The SCSI is an 8-bit parallel, high-level interface. High-level means that instead of a host computer asking for data by specifying a track, cylinder, and sector number, all it asks for is a logical sector number. The SCSI then translates the logical sector number into the actual  disk  location. The  SCSI  also  has  other  improvements  over previous disk drive interfaces. For example, it can transfer data at rates up to 20 megabits per second, handle hard disk drives of almost any size, disconnect itself from the host computer’s bus while it processes requests, and daisy-chain up to eight units off of one controller. 7-23