![HP 28](https://upload.wikimedia.org/wikipedia/commons/0/0b/HP_28.jpg)
The HP-28C and HP-28S were two
graphing calculators
A graphing calculator (also graphics calculator or graphic display calculator) is a handheld computer that is capable of plotting graphs, solving simultaneous equations, and performing other tasks with variables. Most popular graphing calculat ...
produced by
Hewlett-Packard
The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
from 1986 to 1992.
The HP-28C was the first handheld calculator capable of solving equations
symbolically.
They were replaced by the
HP 48 series
The HP 48 is a series of graphing calculators designed and produced by Hewlett-Packard from 1990 until 2003. The series includes the HP 48S, HP 48SX, HP 48G, HP 48GX, and HP 48G+, the G models being expanded and i ...
of calculators, which grew from the menu-driven
RPL programming language interface first introduced in these HP-28 series.
History
Two models were produced, the HP-28C came first in 1987 with 2
kilobytes
The kilobyte is a multiple of the unit byte for digital information.
The International System of Units (SI) defines the prefix ''kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quantitie ...
of usable
RAM
Ram, ram, or RAM may refer to:
Animals
* A male sheep
* Ram cichlid, a freshwater tropical fish
People
* Ram (given name)
* Ram (surname)
* Ram (director) (Ramsubramaniam), an Indian Tamil film director
* RAM (musician) (born 1974), Dutch
* ...
, and was the first handheld calculator with a
Computer Algebra System
A computer algebra system (CAS) or symbolic algebra system (SAS) is any mathematical software with the ability to manipulate mathematical expressions in a way similar to the traditional manual computations of mathematicians and scientists. The de ...
.
A year later, the more common HP-28S was released with 32 KB of RAM and a directory system for filing variables, functions, and programs. The HP-28C used a
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
processor running at 640
kHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is sā1, meaning that on ...
whereas the HP-28S used a custom chip containing an improved Saturn processor core codenamed
Lewis
Lewis may refer to:
Names
* Lewis (given name), including a list of people with the given name
* Lewis (surname), including a list of people with the surname
Music
* Lewis (musician), Canadian singer
* "Lewis (Mistreated)", a song by Radiohead ...
and running at 1
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is sā1, meaning that one he ...
.
The HP-28C was the last HP model introduced with the suffix "C" in its model designation ā a practice which HP had started with 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-65.
To reduce cost ...
back in 1976. The "C" had distinguished those models as having
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 C ...
. However, by 1988 that capability had become so common on calculators that it was no longer a feature of distinction, as it was an assumed characteristic of all serious scientific and business calculators. So beginning with the HP-28S, HP-17B, HP-19B, and HP-27S, the feature suffix "C" was replaced with a class suffix which was more meaningful in the market: "S" for Scientific, "B" for Business, and later (in 1993) "G" for Graphic.
Design
Clamshell
The HP-28 calculators shared a flip-open ("clamshell") case. On the left side of the flip, there is an alphabetic keyboard (in alphabetic order). On the right was a typical scientific keyboard layout.
LCD display
The display was a 137Ć32
LCD
A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liquid crystals do not emit light directly but in ...
dot matrix
A dot matrix is a 2-dimensional patterned array, used to represent characters, symbols and images. Most types of modern technology use dot matrices for display of information, including mobile phones, televisions, and printers. The system is al ...
, usually displaying four lines of information (3 stack/command lines, plus one softkey label line).
Lack of computer interface
Among the drawbacks of the HP-28 was the lack of a computer interface. This meant that stored information could only be entered through the keypad and not backed up.
Weak battery cover
This model (and the
HP-19 series that used the same clamshell design and internals) had one design problem that affected many units: the springs inside the unit that made contact with its three
N-sized batteries made a considerably strong force, and the notches on the case in which the lid edges slid were too thin and shallow. Even if the case itself was sturdy enough, those notches were under extreme pressure, most especially while the user was opening or closing the lid (such as during the replacement of the batteries). As the lid edges were made of a harder metal, the plastic notches in the case were prone to cracking or breaking, even in carefully kept devices.
Surviving examples of the earlier versions of this calculator frequently have rubber bands around or tape over the cover to hold it in place (including the image attached to this article). This defect was later remedied on the HP-19BII, by putting the battery cover underneath the chassis.
Emulators
RPN 28x Calc -- A scientific calculator with a nostalgic, HP-28S-like interface for iPad Halcyon Calc for iPhone, iPod Touch and iPad
See also
*
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 scientific ...
*
Comparison of HP graphing calculators
Comparison or comparing is the act of evaluating two or more things by determining the relevant, comparable characteristics of each thing, and then determining which characteristics of each are similar to the other, which are different, and t ...
*
Graphing calculator
A graphing calculator (also graphics calculator or graphic display calculator) is a handheld computer that is capable of plotting graphs, solving simultaneous equations, and performing other tasks with variables. Most popular graphing calculat ...
*
HP 82240A character set
In computing HP Roman is a family of character sets consisting of HP Roman Extension, HP Roman-8, HP Roman-9 and several variants. Originally introduced by Hewlett-Packard around 1978, revisions and adaptations were published several times up ...
(Modified HP Roman-8)
References
Further reading
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https://web.archive.org/web/20160328183343/http://www.courbis.fr/Data/Books/Pdfs_72/Voyage28/Voyage28_72x72_264_285.pdf -->
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External links
HP-28Spictures on MyCalcDB (database about 1970s and 1980s pocket calculators)
*
ttp://luc.xalasys.com/HP28 The HP28 WWW Archive
{{Authority control
Graphing calculators
28
Products introduced in 1986