Page 64 - Electrical Engineering Dictionary

asynchronous machine See induction Atanasoff is best known for his invention,
machine. along with Clifford Berry, of the first digi-
tal computer, known as the ABC (Atanasoff-
asynchronous operation a term to indi- Berry Computer). Unlike the many World
cate that a circuit can operate or a communi- War II computer pioneers, Atanasoff’s in-
cation system can transmit information when terest in the topic dated to his Ph.D. the-
ready without having to wait for a synchro- sis research at the University of Wisconsin.
nizing clock pulse. After graduation Atanasoff taught physics
and mathematics at Iowa State College and
continued to work on the problem of solv-
asynchronous system a (computer, cir-
ing lengthy calculation by electronic means.
cuit, device) system in which events are not
Legend has it that Atanasoff worked out the
executed in a regular time relationship, that
is, they are timing-independent. Each event basic structure for his new machine while
having a drink at an Illinois road house.
or operation is performed upon receipt of a
Clifford Berry, an electrical engineer joined
signal generated by the completion of a pre-
Atanasoff to help with the construction of
vious event or operation, or upon availability
the device based on Atanasoff’s ideas. John
of the system resources required by the event
Mauchly, another computer pioneer often
or operation.
visited and consulted with Atanasoff. These
discussions resulted in a later lawsuit that es-
asynchronous transfer mode (ATM)
tablished Atanasoff as the first person to build
method of multiplexing messages onto a
an electronic digital computer.
channel in which channel time is divided into
small, fixed-length slots or cells. In ATM
systems the binding of messages to slots is ATM See asynchronous transfer mode.
done dynamically, allowing dynamic band-
width allocation. ATM is asynchronous in ATM adaptation layer (AAL) a layer in
the sense that the recurrence of cells contain- the ATM protocol hierarchy that adapts the
ing information from an individual user is not (small) cell-sized payloads to a form more
necessarily periodic. suitableforusebyhigherlayerprotocols. For
example, AAL5 performs segmentation and
asynchronous updating one unit at a reassembly to map between 48-byte payloads
time is selected from within a neural network and variable length data segments.
to have its output updated. Updating an out-
put at any time is achieved by determining
atmosphere a convenient measure of
the value of the unit’s activation function at
pressure. 1 std atm = 14.696 psia (pounds
that time.
per square inch absolute).
AT bus bus typically used in personal
computer IBM AT for connecting adapters atmospheric attenuation decrease in the
and additional memory boards. It is called amplitude of a signal propagating through the
also 16 bit ISA bus since it presents a data bus atmosphere, due primarily to absorption and
at 16 bit. It presents an additional connector scatter.
with respect to the classical ISA bus (at 8 bit)
of IBM PCs based on Intel 8088. See also atmospheric duct a thin layer of atmo-
EISA. sphere near the earth that acts as a waveguide,
the electromagnetic field, trapped within the
Atanasoff, John Vincent (1903– ) Born: duct, can travel over long distances with very
Hamilton, New York, U.S.A. little attenuation.

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2000 by CRC Press LLC