DISCS DRIVE TO THE LINE

The last of our fast storage series takes the finalists in our disc systems race to their limits.

In the move to smaller and smaller computer systems designers face a problem with disc drives. The 5.25in disc has become the accepted standard and to change it means everyone has to agree on a new one.

As readers will realise, trying to get the computer industry to agree on anything is well nigh impossible. Two designs were originally presented, 3in and 3.5in discs. The business sector is slowly accepting the 3.5in system and now the 3in is proving popular in the home industry with systems available for the BBC, Amstrad and now the Spectrum.

This month, in the final part of our look at fast storage systems, the Statacom and Thurnall interface/drive systems are put under the spotlight.

Statacom supplies an interface which can be purchased separately from the drive and which can run all three sizes of drive, but it is also sold as a package with the 3in Hitachi drive. The Thurnall system is only sold with a drive. Until recently that was the infamous Hungarian MCD drive but from January it is supplied with a 3in Hitachi.

The 3in disc, unlike the 5.25, is housed in a solid plastic casing. The disc surface is protected by a metal shutter which moves out of the way automatically as the disc is inserted. The discs are double-sided, the second side used by taking the disc out of the drive, turning it round, and inserting it the other way up.

Those features make the discs easy to use and carry but also increase the cost. The average price for a 3in disc is around £5.00 while a 5.25 would cost only £2.50. Also most drives, including the Hitachi, can only give 40 tracks which decreases the amount of information they can hold. That was one of the prime reasons why they did not find favour in business.

Regular readers of Sinclair User will remember one of the first disc systems for the Spectrum, that from Interactive Instruments - later taken over by Primordial Peripherals. Those that do will immediately feel at home with the Statacom interface. The two are almost identical, even to having the same error codes, except that the Statacom system, for some inexplicable reason, only allows five characters for file names as opposed to the original six.

On power up, or when a reset button on the interface is pressed, the operating system is loaded into memory. That occupies roughly the top 8K and a number of variables are initialised, taking a further 111 bytes; those can be cleared and the functions called directly. To use the system f$ is set to the file name and then, for Basic, RAND USR bs entered to save and RAND USR bl to load. Code and data are handled in the same way, using cs, cl, as and al. Basic programs cannot be merged.

By adding a number of parameters to f$, for instance LET f$="code,32000,200,32000", the start and length of the code can be specified - the last figure is optional and is the auto-run address. Basic can have a line number added in the same way. Data is handled differently as only dimensioned arrays can be saved; one of the tracks has to be specified as to where the data is saved.

Each track can hold up to 2816 bytes of data, and 39 tracks can be used, the remainder used for the directory. That gives a total of 107.25K of storage per side but it would be very difficult to use all of it. Up to 39 files can be stored, each using one track, but for maximum use they would each have to fill the track. The maximum length code file which can be saved is 11 tracks, 30.25K, and arrays cannot occupy more than one track; for example a single dimension string array cannot be greater than 2808, to allow for system identifiers.

The commands to CAT, format, backup or erase are called using dir, nd, back and zap respectively, the last requiring the file type to be added to f$. The system can, in some cases, be re-initialised by a call to the DOS.

The speed of disc compared to tape is fast but would not win any prizes in the disc Grand Prix. Using the simple test used last month it takes three times as long as the Thurnall system to load - one minute and 23 seconds compared with 37 seconds - and one minute and 42 seconds compared with 59 seconds to save. Erasing also takes longer at 51 seconds compared to 43 seconds. Only format is faster, 29 seconds as opposed to 35.

The disc supplied with the system contains a utility program and 15 Basic games. All of those are called from a menu program and should, in theory, return to it when the game is played. None of the games are particularly exciting - better programs appear in the listings section of Sinclair User - and not all return to the menu. Only a Fruit Machine program is memorable in that it proves impossible to lose money on it.

The interface fits directly onto the back of the Spectrum and has a through port for add-ons; the drive connects via a cable at the back. As mentioned there is a reset button on the top, and there is also a mysterious set of DIP switches to which no reference can be found. No reference can be found either regarding a second drive and so it would appear that only one can ever be used with it.

The Thurnall system uses a very different approach. This time the interface and drive are housed in the same box and the connection to the Spectrum, at the end of a cable, has a through port. The box also has a reset button which will reboot the system, but it can also be used to load a Basic program.

When the system is booted a line of Basic, taking 56 bytes, is entered as line 0. That can be removed, so that no memory is used, by a simple poke. With the line all the normal Spectrum tape commands can be used with the addition of AND FN d() tacked on the end - that can be changed by the user to be any other function. Without it USR 5645 has to be added instead.

A CAT is performed using LIST, LLIST sends it to the printer, and CLEAR is used to format. Files are erased using the normal erase keyword and there is the option of using a wild-card. The minus sign can be used to represent any character so that 'test1', 'test2' and 'test3' can all be erased with the simple 'test-'. A useful feature is that if the file name is given as '----------'' then all the files on the disc will be erased - much quicker than reformatting the disc.

One anomaly is that, unlike tape commands, a file saved using SCREENS must be loaded using it - you cannot use CODE - and you can load just part of a code file. Data is also handled differently. Only dimensioned arrays can be saved, undimensioned strings are dimensioned before saving and multidimensional arrays are changed to a single dimension. Also something saved as a numeric variable can be loaded back as a string variable. That would appear to be a design feature rather than something of great use.

Each side of the disc has 39 available tracks and each holds up to 4K, a total of 156K. When the directory is shown the file name for each track is shown and so may appear more than once - a little confusing. The file names can be up to seven characters and no differentiation is made between upper and lower case. In addition a Basic program, up to 2560 bytes long, can be saved with the file name USR and that is stored on the directory track. When the reset button is pressed that is loaded, and if saved using LINE will auto-run. This is the one program that will also auto-run if merged.

The interface is capable of driving up to two drives and also has a limited RS232 port, set at 1200 baud - limited in that it is monodirectional and so cannot tell if, for example, a printer is busy. It gets round that by having a delay from five to 12 seconds after every return character to allow for the line feed. A return is sent after 64 characters. As with Interface 1 with which it is compatible, listings can be sent with or without the tokens expanded.

If you want a system which will allow you to transfer your commercial programs to disc then you will find little software which will not work with the Thurnall system. The Statacom system, on the other hand, causes problems. Most programs store their code at the top of memory, in the same area used by the system. Some, as with Masterfile, also use f$, which make them doubly difficult, if not impossible to transfer.

The Statacom interface sells for £75.00, or with drive for £240, both plus VAT. The Thurnall system is £219.95 inclusive of VAT and p&p, and is available by mail order.

Before buying any system you should consider carefully what you intend to use the system for. Of the seven systems we have looked at in the series, and there are at least two more in development at the moment, each has its good and bad points.

The Challenge Sprint is cheap and allows most games to be loaded quickly, although it will not be able to handle the new Ultimate games with their non-standard loading speeds.

The Sinclair microdrive is well known and has a few programs available for it. The Wafadrive, although slow, is reliable and good value with two drives, Centronics port and a word-pro program.

Systems which use disc drives have the advantage that when you change computer the drives will still be usable. They may be expensive to begin with but their reliability, low cost discs and disc capacity can soon offset that. If for example, you buy 50 discs, there is a saving of over £150 for the same number of microdrive cartridges.

Of the four disc systems SPDOS from Watford is probably the most technically advanced but uses a lot of memory, as does the Statacom. The other two, from Technology Research and Thurnall, both use very little memory and so are more versatile. With Technology Research there is also a choice of drive and random access.

It would be unfair for us to pick one system in favour of another as everyone will want a system for different reasons. Whatever you choose, and this may be a hackneyed phrase but never more true, it will add a new dimension to your computing. Things that are impossible with a cassette, or would simply take too long, are now within reach. A list of telephone numbers can be kept and loaded in seconds rather than minutes and any number of programs can be chained together to give one long program. Imagine the sort of adventure program which could be written using an 80 track, double-sided drive.

The drawback to all this is that, at the moment, very few software houses are willing to make their software available on anything other than tape. Until they do it is an invitation to users who, having paid good money, break into programs and make copies.

Statacom Distribution, 18 Grove Road, Sutton, Surrey. Tel: 01-661-2266

Thurnall Electronics, FREEPOST, Cadihead. Manchester M30 6DX. Tel: 061-775 7922.

AN EXCITING MACHINE LOOKED AT BY THE ZXC TEAM.

I recently met Chris Drinsmead of Thurnell Electronics and we spent some time talking about their 3" drive unit and the market in general.

A little while ago they produced the first version which sold well, especially in Europe, this was then followed with unit MK2 and has now been superseded by the latest and what is likely to be the final version.

Chris explained, "We have used the experience gained in the making of the other two and the feedback from customers to produce the machine that we believe the market is looking for. The latest version uses no Spectrum memory whatever and is still easy to use, has Hitachi reliability and 300K capacity." Well, I decided to call on the opinions of a general user rather than a hardware expert to put it through it's paces, so over to Tony Woods.

THE DRIVES

In the time that it takes to blink an eye, the Thurnall Disk System will LOAD "Tasword Two" to enable this reviewer to start to type, whereas the lengthy cassette LOADing method enforces a coffee break. It has a similarity to coffee in that its SAVing and LOADing are INSTANT.

The well-packed outfit consists of Hitachi based disk drive power supply, user manual for disk basic and programmers' reference card. With power to the computer and all "add-ons" switched "off", the drive can be plugged into the expansion socket at the rear of the Spectrum and the power supply connected to the mains. Upon switching "on" the legend "Spectrum disk BASIC" can be used, including the cassette tape commands.

The "Welcome" card, after explaining the above, suggests the insertion of the demonstration disk and pressing the black button. Instantly a mnenu appears offering the four options of playing Snakebyte, learning about disk BASIC, MERGing and zero memory for EXITing.

The game Snakebyte allows Thurnall to demonstrate the speed of access of the system, with four instruction screens and an offer to choose a level of difficulty preceding the games screen. Learning about disk BASIC from the nine screens, some with four extra sections each added by pressing a key, is simple as these instructions are clear, well-designed and not too wordy. It firstly explains how to LOAD and SAVE, and then how to save and load television pictures, numeric arrays, strings and string arrays, and finally for Code and how to reassign new addresses.

I was now eager to try my new toy and set off, clutching my box of goodies, to pay a quick visit to my local computer expert who, in double-quick time, altered lines in "Tasword 2" to enable it to LOAD and SAVE on disk. He made it appear so easy and explained how it was done, line for line - so that I could adapt other programs. When I reached the safety of my own computer and reconnected all the equipment, I could not remember how to use all the POKEs and MERGEs that he had mentioned!

Thus it was that I was forced to approach the "User Manual", which fills in the gaps left by the "Programmers' reference card" and the introductory program. I would have liked to see a larger format manual than half A5, the use of larger type than 8pt and an appreciation of the problems experienced by some of us slow learners. So I donned my spectacles and proceeded to learn that the thin black button ejects disks, that the black button on the left makes the computer load from disk and is called the reset button, and that the commands in disk BASIC resemble their cassette counterparts with the addition of "AND FN d ()". This is going to be a piece of cake, I thought to myself, and read on.

AUTO EXECUTION

Next, I was introduced to making programs self-executing after they have been loaded, by the addition of "LINE n" to the SAVE and LOAD statements. Not only was I then shown how to SAVE and LOAD pictures, but also given a five line picture program to try, and - it worked, just as the manual said that it would. There, in the directory, was the evidence in the form of "picture screens$". On to numeric arrays, with a possible modification to the LOAD command in order to load only the desired numbers by the inclusion of "DIM a(n);" before the normal DATA loading command.

I fairly sailed through strings, string arrays and code to arrive at page ten breathless, to find instructions on how to SAVE and LOAD my own startup program. Rubbing my hands with glee, thinking that this was more like it - really using the disk unit at last, I entered the two line program and "SAVE "USR" AND FN d() LINE 10" and then pressed the black button. There on the screen were the words that I had typed in! This was followed by the LIST command that prints out the names of what is stored in each of the forty-four portions of side A of the disk, each one representing 3.25 kilobytes of data.

How to ERASE a file came next, complete with a means of CLEARing a whole disk, which is something that must be done to all new ones. Then there were instructions on how to transfer a program from cassette to disk by first using the MERGE command, giving access to disk BASIC, and then the usual SAVE command.

I was now at page sixteen and had not become lost in any of the above, as the descriptions were very clear and concise. Here were three pages on reports and error messages that appear at screen bottom, giving their meanings and the situations when they occur. The last six pages consisted of an explanation of how to add the access to disk BASIC to programs in other places than line one, how to have random access disk files in disk BASIC and some technical data for the more experienced user.

But, sad to relate, nowhere are there instructions on how to SAVE all those programs that I have bought and take three to four minutes to LOAD from cassette. Why have such a superb system at our disposal, giving instant retrieval of information and programs, if they can only be used with "homemade" programs? Do software houses really believe that every Tom, Dick and Harry are going to rush out and invest vast quantities of cash on a disk drive in order to copy their friends games and the like? As most games players are children or teenagers it would seem unlikely. Having purchased a games program it would be ideal to be able to put it onto disk for instant LOADing, without having robbed the manufacturers of their cash. I should think reviewers would find it a boon!

Interestingly Thurnell are negotiating with a software house with a view to producing a "tape to disk" program, which should be worth waiting for, and they can already supply Tasword II and Masterfile in disk versions if required.

The complete units costs £219.95 and is only available from Thurnell directly at the moment.