HP-25
Encyclopedia
The HP-25 was a hand-held programmable scientific/engineering calculator made by Hewlett-Packard
between 1975 and 1978. The HP-25 was introduced as a cheaper (US$195 MSRP) alternative to the ground-breaking HP-65
.
To reduce cost, the HP-25 omitted the HP-65's magnetic card reader, so it could only be programmed using the keyboard. After switching off, the program was lost and had to be typed in again. The model HP-25C, introduced in 1976, addressed that shortcoming through the first use of battery-backed CMOS
memory in a calculator, termed continuous memory by HP.
Like all early HP calculators, the 25 used the Reverse Polish Notation
(RPN) for entering calculations, working on a four-level stack
(x,y,z,t). Nearly all buttons had two alternative functions, accessed by a blue and yellow prefix key. A small sliding switch was used to change between "run" and "program" mode. The HP-25 used a 10-digit red LED
display and was the first calculator to introduce the "engineering" display option, a denormalized mantissa/exponent format where the exponent is always a multiple of 3 to match the common SI prefixes
, e.g. mega, kilo, milli, micro, nano.
The HP-25 had memory space for up to 49 program steps. It was the first HP calculator which used fully merged keycodes (storing prefix key and function key together in one program location) to save memory space. Additionally there were 8 storage registers and specialized scientific and statistical functions. The owner's manual came with 161 pages in four colors and contained many mathematical, scientific, navigational and financial programming examples.
The HP-25 was about 25% smaller than the HP-65. One unusual thing about the ergonomics is that the key faces have the profile of a trapezoid. The HP-25 was a competitor to the TI-58 and TI-58C calculators offered by Texas Instruments.
One notable deficiency of the HP-25/25C was the lack of a subroutine capability. The competing TI-58 and even the earlier SR-56 had subroutines. Although 49 fully merged keycodes were roughly equivalent to the unmerged 100 steps of the SR-56; by the time the TI-58 arrived with 480 steps, subroutines, DSZ loops, etc, the HP-25/25C had serious competition. HP would go on to introduce the HP-29C/19C calculators with 99 merged steps, labels, and subroutines. And TI would introduce a TI-58C with continuous memory.
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
between 1975 and 1978. The HP-25 was introduced as a cheaper (US$195 MSRP) alternative to the ground-breaking HP-65
HP-65
The HP-65 was the first magnetic card-programmable handheld calculator. Introduced by Hewlett-Packard in 1974 at an MSRP of $795, it featured nine storage registers and room for 100 keystroke instructions. It also included a magnetic card reader/writer to save and load programs...
.
To reduce cost, the HP-25 omitted the HP-65's magnetic card reader, so it could only be programmed using the keyboard. After switching off, the program was lost and had to be typed in again. The model HP-25C, introduced in 1976, addressed that shortcoming through the first use of battery-backed CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
memory in a calculator, termed continuous memory by HP.
Like all early HP calculators, the 25 used the Reverse Polish Notation
Reverse Polish notation
Reverse Polish notation is a mathematical notation wherein every operator follows all of its operands, in contrast to Polish notation, which puts the operator in the prefix position. It is also known as Postfix notation and is parenthesis-free as long as operator arities are fixed...
(RPN) for entering calculations, working on a four-level stack
Stack
-Mathematics:* Stack , general category-theoretical concept to formalise "pull-back" operations in geometry and algebra* Algebraic stack, a generalisation of scheme and algebraic space in algebraic geometry; a specific type of the above-Computers:...
(x,y,z,t). Nearly all buttons had two alternative functions, accessed by a blue and yellow prefix key. A small sliding switch was used to change between "run" and "program" mode. The HP-25 used a 10-digit red LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
display and was the first calculator to introduce the "engineering" display option, a denormalized mantissa/exponent format where the exponent is always a multiple of 3 to match the common SI prefixes
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
, e.g. mega, kilo, milli, micro, nano.
The HP-25 had memory space for up to 49 program steps. It was the first HP calculator which used fully merged keycodes (storing prefix key and function key together in one program location) to save memory space. Additionally there were 8 storage registers and specialized scientific and statistical functions. The owner's manual came with 161 pages in four colors and contained many mathematical, scientific, navigational and financial programming examples.
The HP-25 was about 25% smaller than the HP-65. One unusual thing about the ergonomics is that the key faces have the profile of a trapezoid. The HP-25 was a competitor to the TI-58 and TI-58C calculators offered by Texas Instruments.
One notable deficiency of the HP-25/25C was the lack of a subroutine capability. The competing TI-58 and even the earlier SR-56 had subroutines. Although 49 fully merged keycodes were roughly equivalent to the unmerged 100 steps of the SR-56; by the time the TI-58 arrived with 480 steps, subroutines, DSZ loops, etc, the HP-25/25C had serious competition. HP would go on to introduce the HP-29C/19C calculators with 99 merged steps, labels, and subroutines. And TI would introduce a TI-58C with continuous memory.
External links
- The Museum of HP Calculators' article on the HP-25
- 1975 HP Calculator Christmas Guide
- HP-25 and HP-25C pictures on MyCalcDB (database about 70's and 80's pocket calculators)
- HP-25 hardware details
- HP-25 Brochure from Hewlett-Packard