FEATURES OF THE ELLIOTT 502
Designed for the job
502 is basically a very fast general purpose computing machine having storage,
arithmetic, input, output and control facilities, but is specifically designed
for real-time, on-line data-processing appliations.
Features essential to on-line operations of varying time dependence
permit the simultaneous running of a number of programmes on a
Programmes dealing with different components of the system under surveillance
are allocated[,] priority ratings according to the urgency with which
they must be obeyed.
The 502 incorporates a facility known as Programme Break
which enables a high priority programme to take precedence over one of
lower priority in response to an external stimulus.
Compound immediate access store
The internal storage system of the 502 contains a fast section
with a very short cycle time, but of limited capacity,
and a larger section of slightly longer cycle time.
The capacity of the main section may be extended to any
Instructions may be taken for either store, and may operate
on data from either store.
Elliott ultra-high-speed logic elements, assembled in a fully parallel
pure binary system of an intrinsically elegant design, impart to the 502 the
maximum attainable operating speed.
Operation time for simple arithmetical functions on operands in the fast store
is only 2.0 microseconds, including access time of instructions.
Long functions such as multiplication and division take about
10 microseconds only.
When both instructions and operands are obtained from the main store, the
corresponding times are of the order of 7 and 14 microseconds.
The short word length of 20 bits, used throughout the 502, is entirely
adequate for the majority of on-line control applications.
The instuction code includes facilities for double-length
multiplication, division and shifting functions.
Automatic data transfers
Data transfers between the 502 and its peripheral equipment are aided by the
provision of a semi-automatic transfer facility, which allows
transfers of data to take place on demand of the peripheral equipment.
Page created by Bill Purvis, last update: 20th November, 2003