1.8 H

 

half cell - a probe that will generate a voltage proportional to the hydrogen content in a solution.

 

half duplex - see HDX

 

handshake - electrical lines used to establish and control communications.

 

hard copy - a paper based printout.

 

hardware - a mechanical or electrical system. The ‘functionality’ is ‘frozen’ in hardware, and often difficult to change.

 

HDLC (High-level Data Link Control) - an ISO standard for communications.

 

HDX (Half Duplex) - a two way serial connection between two computer. Unlike FDX, characters that are sent are not reflected back to the sender.

 

head - pressure in a liquid that is the result of gravity.

 

hermetic seal - an airtight seal.

 

hertz - a measure of frequency in cycles per second. The unit is Hz.

 

hex - see hexadecimal.

 

hexadecimal - a base 16 number system where the digits are 0 to 9 then A to F, to give a total of 16 digits. This is commonly used when providing numbers to computers.

 

high - another term used to describe a Boolean true, logical positive, or one.

 

high level language - a language that uses very powerful commands to increase programming productivity. These days almost all applications use some form of high level language (i.e., basic, fortran, pascal, C, C++, etc.).

 

horsepower - a unit for measuring power

 

host - a networked (fully functional) computer.

 

hot backup - a system on-line that can quickly replace a failed system.

 

hydraulic - 1. a study of water 2. systems that use fluids to transmit power.

 

hydrocarbon - a class of molecules that contain carbon and hydrogen. Examples are propane, octane.

 

hysteresis - a sticking or lagging phenomenon that occurs in many systems. For example, in magnetic systems this is a small amount of magnetic repolarization in a reversing field, and in friction this is an effect based on coulomb friction that reverses sticking force.

 

Hz - see hertz