Computers are getting smaller every day. Stuart Cooke looks at three micros that literally fit in your hand.

With technology galloping ahead at a rapid pace, hand-helds are getting smaller, thinner and cheaper.

Psion and Epson have produced the latest machines and, with the current trend, calculators could become a thing of the past as programmable computers take their place. The main reason for this shift is that these wallet-sized computers have portable proceddors which can be used as a database or to work out complicated calculations. And many allow users to write programs of their own.

Psion, known by every computer buff for its involvement with Sinclair Research and its production of software for the Spectrum and the QL, has launched its own computer.

Psion claims the "Organizer" is "your personal database for vital day-to-day information with the programming power of a desktop microcomputer." This is probably over generous: the Organiser does allow you to store and retrieve data as with a database, but the power of a desktop is stretching it.

The Organiser is supplied in a black plastic case that slides over the keyboard when the computer is not in use. It measures 14cm by 8cm, slightly smaller than the average paperback book, and even though it does look large it can fit quite easily into an inside jacket pocket.

The bottom of the machine sports what Psion calls "solid state drives". These are spaces for two slot-in program packs. Inside the program pack is a standard EPROM. This means it's possible to get a lot of storage on one drive - one 8K data pack is supplied with the machine and you can purchase more of these as you need them.

The display is a 15 character LCD. When the machine is first powered up this displays a 24-hour real-time clock and calendar.

The small pocket-size manual's 42 pages contain all the information you need to use the machine, and it's all easy to find.

Chapters deal with each separate keyword in detail. The manual for this micro is no more complicated than one for a simple pocket calculator.

A quick examination of the machine reveals that the keyboard is not laid out in a standard QWERTY format but is alphabetic. Great if you've never used a typewriter but it leads to reciting the alphabet to yourself if you have.

Once powered up, the clock is displayed. Unfortunately, even though there is an 'on' key, there's no 'off'. Turning the machine off requires a minimum of three key presses, so the idea of quickly and conveniently looking at the time is spoilt.

Pressing the Mode key shows you all the main functions you can use, and Enter allows you to type data into the machine. If you then press the Save key followed by Execute the information typed is stored in the machine for retrieval at will. Another push on the Mode key reveals the word off; now press Execute to switch off the machine.

Calc is the next main function. This allows the user to enter arithmetical calculations, making the Organiser a glorified pocket calculator.

The Find key allows you to enter a sequence of characters, and the machine then searches through all the strings stored in the EPROMs and finds the first one that contains a match. This is where one of the main limitations of the Organiser comes to light.

Supplied with the review machine was a datapack with a database containing a number of restaurants in the London area. Say you wanted to find a Chinese restaurant: you would type in 'Chinese' to the Find prompt after which the machine would list all the Chinese restaurants in its memory. If, however, your Chinese restaurant had to be in a certain area you'd be out of luck. You can't search for a string using two parameters, so you must look through all the entries till you find one in W1, for example. Of course you could always search for W1 and then cycle through entries looking for a Chinese one.

The main problem with the data packs is that they are actually EPROMs. It is very simple to store data in them, remove them from the machine and put it in your pocket until you need the information stored on it. The problems occur when you want to delete information. You can mark the data as deleted but it still takes up some of the valuable memory in the pack. The only way to reclaim this lost data is to erase the EPROM.

This can be done either by buying Psion's eraser which clears two EPROMs at once, or sending your data pack to Psion for erasure, which costs you money. Of course, erasing an EPROM wipes out all the data held in it.

The Organiser has no built-in programming language. If you wish to write your own routines for use with the machines you need to purchase one of the program packs available. All the program packs contain a number of new routines for the computer such as PROG which allows you to write a program, CAT which tells you what programs are stored and RUN which executes a named program.

The language used on the Organiser is one of Psion's own design called POPL. This appears to resemble that tried and tested language Basic. However, POPL has no line numbers and all GOTOs are made to labels. Commands exist to print out on the display, input characters from the keyboard, perform loops and compare data. It is even possible to write programs that call other programs, passing parameters between them.

POPL is easy to use, though the small display on the computer makes it difficult to remember what you've typed and to edit the programs.

Each of the program packs has a number of routines already added to the Basic. A science pack contains many scientific functions and programs of use to a scientist. The Finance pack, supplied for review, contained programs to work out mortgage repayments, cashflow repayments, etc.

As well as the programs, a number of science and maths functions have been added which you can use with your programs such as SIN, COS and FAC.

The supplied pack being the finance one doesn't mean yoou can't now write scientific programs; it just means you don't get the extra programs supplied with the science pack.

Even when all the gripes about no 'off' switch and the problems with the datapacks are taken into consideration the Organiser is still a simple to use and convenient computer. I doubt I'll be carrying a diary or address book with me in future.

No bigger than a wallet, the Casio FX-750P is most definitely a pocket computer.

Most of the low-priced pocket computers have a small amount of internal RAM with the option of purchasing an additional RAM pack to fit inside the machine. Not so the latest machines coming out of the Casio stable. The FX-750P has a couple of 'drives' built into the front edge. These drives are usd for insertion of RAM cards, as the machine has no internal memory of its own.

Two types of RAM card are available for the 750, the RC-4 gives 4K of memory while the RC-2 gives 2K. Both types of RAM card look exactly alike, being slightly larger than a book of matches. The RAM cards have their own internal battery and so can be removed from the machine without fear of losing the programs stored in them.

Programs and variables are stored in a very useful fashion. If you have two RAM cards installed in the machine, programs are stored in the card in slot 0 and all data is stored in the card in slot 1. The manual shows you how this can be used to advantage. If, for example, you needed to manipulate a large amount of sales data you could install the card to hold the data in slot 1 and have a number of different cards for use in slot 0. These cards could hold programs for inputting the data, sorting the data and searching the data. The other way of using this feature would be to have one program which would use a number of different sets of data stored on separate cards.

Writing programs for the FX-750P couldn't be easier - you just program in Basic.

The Basic supplied is a fairly standard implementation, but there are quite a few additional useful extras. Anyone who requires a machine that performs statistical calculations will not be disappointed. Commands exist to SUM data and calculate standard deviation as well as other statistical functions. Engineers are also catered for and all the standard trigonometric functions exist together with a number of constants such as the acceleration of free fall and the Avogadro constant to make life easier.

A book of programs is available covering a wide range of subjects for those without programming experience. You just ype them in and you're away. On the other hand, if you want to learn Basic the manual is very good. Almost every step mentioned is accompanied by a picture of the contents of the display at that moment which makes the text easy to follow and reassures you that you are going about the latest task correctly.

Keeping all your data on RAM cards is a little dangerous, especially when the battery needs changing. To facilitate the storage of your programs and data onto cassette, Casio has developed the FA-20 interface.

The FA-20 is supplied in a plastic case which takes the power supply, cassette leads and spare RAM cards. The FX-750P simply slots into the interface and can be kept in position for handy storage. The FA-20 doesn't contain its own cassette; it simply allows you to connect a standard cassette recorder to your pocket computer - so the overall package isn't quite as compact as it would seem.

The Basic supplied on the 750 allows you to save all the files on a card, the current file, all the data or just selected items of data. This gives a very versatile storage system which proved to be reliable, if a little slow. However, you won't be saving programs onto cassette every day as all data can be stored on the RAM cards.

As well as giving you cassette storage the FA-20 also has a built-in thermal printer which allows you to get listings of your programs and output data. Again the printer is a little on the slow side and the text is extremely small, but it does work well and is far cheaper than any other.

Although the FA-20 has a mains unit, rechargeable batteries are built into the unit and it can be used without a mains supply.

The FX-750P is a very handy little machine. Write a simple memo program and you just need to carry a number of RAM cards instead of a diary. For engineers, or anyone doing a number of calculations on the move, this machine could prove an invaluable tool.

The smallest of the two machines from Casio is the FX-720P. This handheld closely resembles the FX-750 except for the keys. However, part of the reduction in price is due to the inclusion of only one RAM card drive.

One function on the FX-720, not found on the FX-750, is the Memo function. Use of the memo bank turns your scientific pocket computer into a portable database.

To enter data into the memo bank just go into Memo in mode by pressing two keys. Then simply type in your memo, be it an address, message or anything else. Separating the fields by commas allows simple manipulation of stored data at a later date.

To search for information, a press of the Memo key displays record number one. Pressing the Exe key cycles through the rest of the files. When you find the file you want, use the Memo key to reveal the remainder of the file.

This method of reading a file is a bit long-winded, so Casio has included a search facility using a string of characters which you input: it is very easy to use. If, for example, you wish to search your files for the address of Casio - you would type in CASIO and press Memo. The FX-720 searches for the first record that contains the string CASIO and display it.

Like the other Casio portable computers you can write your own programs in Basic. The Basic included on the FX-720 has extra facilities to allow you to access your memo files from within a program. All the normal standard Basic functions are there, including a full set of trignometrical and scientific functions.

Three manuals are supplied. One is an introduction to the computer and Basic, the second is a reference manual for the Memo Pad and the third is a library of programs to type in. All the manuals are well-produced and extremely easy to understand; all responses made by the computerare shown by diagrams of the display. The program library covers subjects as diverse as games and medicine. All the programs are clearly documented and even show which keys to press to run the programs.

Even if you've never used Basic, you should be able to use the wealth of programs supplied in this book and you may even learn a little about writing programs while you're at it.

Although it doesn't offer the storage that the FX-750 does, this machineis still extremely useful. Having the memo bank installed as a feature rather than having to write a program is convenient, whether you want to store names and addresses or write messages.

These three hand-held micros are the shape and size of things to come. When memory packs become larger and cheaper, as they will, why should anyone carry around sheaves of paper and books when all the information could be fitted into a pocket?

Each of the three appears to be designed for a particular kind of user. The Psion Organiser, for instance, would probably not be bought by an engineer, but it does offer a great amount of data storage. The price, however, may put a few people off when compared with other machines.

The FX-750 would be excellent for an engineer, for instance. A fairly large amount of storage is available in the two drives and the way information can be moved around is useful. On the other hand, the FX-720 offers some of the features of both machines and at a much lower price. Granted, you can't store as much information as on the Psion, but you could always carry a number of the RAM cards with you.

Perhaps the greatest advantages of the Casio are the main dislikes of the Organiser. You can program in Basic and you can carry around a number of RAM cards from which the information can be easily altered without returning them to the manufacturer or buying yet another piece of equipment to wipe them.