The term continuous memory was coined by
Hewlett-Packard (HP) to describe a unique feature of certain
HP calculators
HP calculators are various calculators manufactured by the Hewlett-Packard company over the years.
Their desktop models included the HP 9800 series, while their handheld models started with the HP-35. Their focus has been on high-end scienti ...
whereby the calculator could internally sustain most, or in later models - all, of the contents of user memory (via battery-backed
CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss
", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...
memory). Since its introduction on the
HP-25C
The HP-25 was a hand-held programmable scientific/engineering calculator made by Hewlett-Packard between early January 1975 and 1978. The HP-25 was introduced as a cheaper (US$195 MSRP) alternative to the ground-breaking HP-67. Similar to the ...
, this feature slowly evolved by model to eventually mean maintaining the contents of nearly all calculator memory, including system and scratch RAM, options, settings, flags, and other calculator state information.
Before the introduction of the HP-25C in 1976, all calculator
random-access memory (RAM) was volatile, i.e. its contents (esp. user data in storage registers and any user programs) were cleared when the calculator was turned off. Three early models with this improved, continuous memory - the HP-25C,
HP-29C, and
HP-19C - actually had the words "'' Continuous Memory ''" printed in conspicuous, white script on the bottom margin of their faceplates. The "C" in the model designations was to distinguish those models within HP's calculator product line. HP did not print this phrase on subsequent, featured models because the novelty of continuous memory had by then faded and also because it could no longer claim it as a feature unique to HP calculators (Texas Instruments would later call their identical feature "
Constant Memory"). At introduction over the next 9 years (approx. 1979–1987), subsequent HP models so featured simply had designations in which the letter "C" followed the model number, e.g. the
HP-34C
The HP-34C continuous memory calculator is an advanced scientific programmable calculator of the HP 30 series. It was produced between 1979 (cost US$150) and 1983 (cost US$100).
Features Root-finding and integration
Significant to the HP- ...
and the
Voyager series HP-10C
The Hewlett-Packard Voyager series of calculators were introduced by Hewlett-Packard in 1981. All members of this series are programmable, use Reverse Polish Notation, and feature continuous memory. Nearly identical in appearance, each model ...
,
HP-11C
The Hewlett-Packard Voyager series of calculators were introduced by Hewlett-Packard in 1981. All members of this series are programmable, use Reverse Polish Notation, and feature continuous memory. Nearly identical in appearance, each model ...
,
HP-12C
The HP-12C is a financial calculator made by Hewlett-Packard (HP) and its successor HP Inc. as part of the HP Voyager series, introduced in 1981. It is HP's longest and best-selling product and is considered the '' de facto standard'' among fin ...
,
HP-15C
The HP-15C is a high-end scientific programmable calculator of Hewlett-Packard's Voyager series produced between 1982 and 1989. The "C" in the name refers to the continuous memory, such that the calculator retains it's state when switched off.
...
and
HP-16C
The HP-16C Computer Scientist is a programmable pocket calculator that was produced by Hewlett-Packard between 1982 and 1989. It was specifically designed for use by computer programmers, to assist in debugging. It is a member of the HP Voyager ...
.
References
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{{HP calculators
continuous memory The term continuous memory was coined by Hewlett-Packard (HP) to describe a unique feature of certain HP calculators whereby the calculator could internally sustain most, or in later models - all, of the contents of user memory (via battery-backed ...