Electronic calculators reached their zenith in 1981 with the introduction of the HP 12C financial model. Despite the remarkable improvement in digital electronics, the HP 12C remains in production, little changed to this day.

I bought an HP15C, the engineering contemporary when it was introduced in 1982. While this model ceased production in 1989, nothing sold since has given me cause to update. It appears that the calculator cannot be improved upon despite a quarter of a century of technological advances. This has let me to wonder when I will buy my ultimate PC.

The first calculator was the abacus, constructed with wood and using beads to perform additions and subtractions. In 1622 the slide rule performed multiplications and divisions. Mechanical adding machines were available at the start of the 20th Century and the first electronic calculators appeared in the 1940s. The first desktop electronic calculators were sold in the mid-1960s.

These were so expensive that the cheaper mechanical adding machines continued to be available. Pocket electronic calculators appeared by 1970, and while still expensive, had replaced mechanical adding machines due to their falling price, portability and functionality. The pocket calculator could add, subtract, multiply and divide -- the four arithmetical functions.

Today, most people own a simple four-function calculator, as well as a mobile phone and personal computer, each including a built in four-function calculator. So, for most calculator users, developments after 1970 were of little significance other than to reduce price.

Pocket calculators of the early 70s were too expensive for school students and it was not until near the end of my high school years that I could replace my logarithm tables and slide rule. But calculator advancement still had a decade to go.

Hewlett Packard launched the first scientific handheld calculator in 1972. The HP-35 included trigonometrical (sin, cos and tan) and logarithmic functions in addition to the regular arithmetic functions.

The HP-65, released in 1974, was the first scientific programmable calculator. It had a card reader, and could store 100 instructions, including ones for decisions and conditional branching. The smaller and cheaper HP-25C, introduced a year later heralded the first "continuous memory" programmable.

It did not have a card reader, instead user programs could remain in memory even when the calculator was turned off. Like most of the calculators of the 1970s, the HP-35, 65 and 25C used red LED 7 segment displays. This coupled with their N-MOS electronics meant that battery life was measured in hours. Since a programmable calculator was left on continuously while programs were written and run, a mains power adapter was a must.

Lower power consumption Liquid Crystal Displays (LCD) and C-MOS electronics appeared in calculators by 1980 setting the stage for the final significant improvement in the state of the art. Battery life was now measured in months or years, obviating the need for a mains power adapter. Hewlett Packard released many models in the early 80s, but it's 10 series, including the 12C and the 15C made the most of the benefits of the new technologies. Low power consumption allowed long battery life from tiny camera batteries.

Some infrequent users have reported that their 12Cs were still working on their original set of batteries over 20 years after purchase. HP chose a landscape format for the calculator to allow for a longer display while keeping the calculator small.

Like many HP products, the 10 series was made to be very durable with reports of one, belonging to a zoo keeper, surviving a trip through the digestive system of a hippopotamus.

Both the HP12C and HP15C were programmable, with user programs remaining in continuous memory for as long as the batteries lasted. Calculator programming was a matter of telling the calculator to remember a series of key strokes and then replaying them on what ever data was presented. All inputs and results were expressed as numbers.

While not as sophisticated as a Third Generation computer programming Language (3GL), the HP15C supported conditional branching, subroutines, indirect memory addressing and labelled jumps. In the 80s I wrote a handful of programs for my 15C to support engineering design calculations as well as whimsical, number-oriented games programs such as lunar lander and cows & bulls (Mastermind).

Further advances were made in programmable calculators including: support for alphanumeric data; graphical data representation; and programming in BASIC, a 3GL. These advances were of little appeal in the 1980s since this was the decade of the personal computer. Mass produced Personal Computers were introduced in 1976 with the Apple II and by the early 80s, and with the imprimatur of IBM, PCs proliferated.

The application that propelled the acceptance of PCs was the spreadsheet, and it was this that replaced all but the most basic four-function calculator for most users.

PC users, almost from the start, sought out standards that would allow them to access programs from a variety of commercial and hobbyist sources. The Control Program for Microcomputers (CP/M) was an early operating system released commercially in 1976 and available to run on hardware from companies such as DEC, HP, Apple and a host of long since defunct companies.

CP/M machines were used as word processors 60 per cent of the time. The most popular word processing program of the day was WordStar from MicroPro. Most of the rest of the time CP/M machines were used to run spreadsheets such as Visicalc from VisiCorp, or Databases such as dBase from Ashton-Tate -- and of course there were the games.

The new PC era was characterised by obsolescence. Advancement was so rapid that any system more than two years old was regarded as unusable. Within 12 months of the launch of Microsoft's and IBM's MS/PC DOS in 1981, CP/M was almost completely replaced as the de facto standard PC operating system.

Advancements in early computers brought real benefits to users. 8" floppy disks were replaced by 5 ¼" and then 3 ½" disks making them easier to handle. Floppy disk capacities went from 360KB to 1.2MB to 1.44MB, and from being the only disk drive available, to becoming a device to backup or transfer files from the new Winchester hard disk drives.

The first PC I had with a hard disk drive, had a storage capacity to 20MB. My previous machine had only dual 264KB floppy drives, one holding the operating system and applications and the other for data. At the time, I thought it was ridiculous to waste a 20MB disk on a single user.

Soon, colour and graphical user interfaces replaced my green character mode display. With each improvement in processing speed and memory capacity the industry found new functions I didn't know I needed. My word processor now had to be WYSIWYG, including the ability to display and print graphics. My computer had to be part of a network so I no longer needed to share files by floppy disks (sneaker net). Then my computer had to handle sound, photographs and video. And on it went.

The mid 90s saw the explosion of the Internet, courtesy of the Web. With this, the focus of the technology began to shift. The PC was becoming a device for accessing the Web. Advancement continued but the useful life of a PC began to grow.

Friends who once scorned any PC more than two years old now held onto machines for four years. The rationale for each upgrade became more emotional and less, well, rational. As in the days of CP/M, PC's are used most of the time as word processors. The second most common use is now to access the Internet for e-mail and the Web, followed by spreadsheet use.

The four key PC functions of today, ie word processing, e-mail, Web and spreadsheet, can also be found in top-of-the-line mobile phones. In some parts of Asia, mobile phones have already started to replace PCs as the computing platform for most users.

I don't expect that mobile phones will ever completely replace PCs. PCs will remain available configured as basic four-function devices. Advanced PCs and esoteric application software will continue to be developed, but they won't be sold at department stores.

We'll also still buy four-function calculators; scientific calculators will remain available in newsagents and department stores, bought almost exclusively for high school students.

Today you won't find a programmable calculator for sale anywhere but specialty stores, or on the Internet. There, among the very limited range, you'll find the HP12C.