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ComputerAnswers Column 23


COMPUTER ANSWERS NOVEMBER 1986



Copyright 1984-1989 Simon N Goodwin

(* SUB: This column is shorter than usual so that we can use up the overmatter from last issue; two pieces headed 'Computers and Video' and 'The incompatible Einstein'. As usual, the 'Feedback' refers to past issues, so it would be wise to get it into the next available column. Thanks *)

TRANSFER TRAUMAS

I am the owner of an Amstrad 6128 which is supplied with CP/M plus and CP/M 2.2. My girlfriend's father has just bought an Amstrad 8256 which comes with a disk labelled CP/M plus. I was under the impression that this was a standard operating system, but my 6128 tells me that the 8256 CP/M disks were not formatted and the 8256 displayed 'This program will not run in this environment' when when I tried to run 6128 programs on it.

Is the difference in the actual systems or in the formatting?
Simon Ivory, Sunderland, County Durham.

Amstrad have changed their formatting policy with each new machine - 464, 6128, and 8256. This makes life fairly complicated, but it is still possible to swap disks between machines if you're careful.

The 8256 is capable of reading disks produced on the 6128, and most disks formatted on the 464. The only disks that won't work on the 8256 are ones produced in 'IBM format' on the 464. This doesn't matter much, as virtually nobody used that format.

The 6128 can't read 8256 disks, but it can read every variety of disk from its predecessor, the 464. I wish Alan Sugar had pushed his keep-it-simple ethos a bit further and called the machines 1, 2 and 3; it might have been honest to give the 664 the number 2.5! Amstrad's technical whizz Vic Oliver summed all this up by telling me that everything will be hunky dory as long as you format all your disks on the 8256, but on re-reading his explanation I suspect that this wall of digits has baffled him as well. It seems more likely to me that your best bet is to format disks on the 6128, especially in view of your own discoveries.

The message about the 'environment' is nothing to do with the disk format, but just an indication that the program you are trying to run on the 8256 requires special hardware features, such as colour graphics. These differ from one machine to the next, for obvious reasons. You can't always run programs that rely on those features on different machines, even though the format of files may be the same on both systems.

CP/M plus does not specify the graphics format of a system at all. The only programs that are sure to run on any CP/M machine are ones, like Supercalc and Wordstar, which confine themselves to a text display. You should not have any trouble transfering those programs from one Amstrad to another, as long as you get the disk format right.

There is a standard for graphics, called GSX, but it is rather restrictive and not widely used. Programs written for GSX will run on any other machine with an appropriate (machine-specific) version of GSX loaded. The number of dots on the screen may vary from one machine to the next, but the displays will look similar on any system with GSX. You will also be able to use a wide variety of plotters and printers, as GSX provides a standard way of talking to any graphics output device.



INSURING YOUR MICRO

Could you please advise me about PC insurance. I need to know what to insure for and against, and which insurance companies offer cover specifically for PCs and peripherals.
I.M Cutler, Wrexham, Clwyd.

I wrote a long answer to a similar question in August last year, but the time is probably right for a brief update.

It is almost impossible to get a special insurance policy for home computers and personal machines, unless the total value of the system is at least £2,000. A few firms will let you include a a micro in the 'home contents' policy which covers the rest of your belongings, but many firms specifically exclude cover on home micros; others may limit the cover or charge a specially-high rate. It is virtually impossible to insure a cheap system against breakdowns - insurance underwriters have found that it is not worth their while to take on such business.

If you rely on a small computer you should consider buying a 'spare' one - which may be cheaper than a year's insurance for a larger system - or coming to an arrangement with a local dealer so that you can borrow a machine if yours has to be sent away for repairs. This is one area where you can benefit from shopping at a local, independent dealer rather than a High Street box-shifter.

Maintenance contracts are uneconomical for small machines, but repairs are usually cheap, partly because the upper limit on price is just the replacement cost of the hardware. The electronic parts of small computers tend to fail in the first few months - during the warranty period - or not at all, but mechanical problems with keyboards, disks, printers and connectors can crop up at any time, particularly if you move the machine about.

If your system is worth more than £2,000 you should compare the advantages of insurance and a maintenance contract.

A basic insurance policy will cover breakdowns, but it will be up to you to find a repair firm and send the bill on to the insurance company. The next step up is an 'all risks' policy; the insurance company will replace your hardware and commercial software if it is damaged, stolen or incinerated. The ultimate insurance policies cover 'additional expenses' such as the rental of a spare machine and data-entry costs if your hard disk contracts amnesia after a head crash. Insurance policy prices average about six per cent of the purchase price of the whole system, but prices vary widely depending upon the hardware and the address.

Maintenance contracts tend to be more expensive, but not much. The big advantage is that - you are assigned an appropriate repair agency when you sign up, so you know who to contact at once if you get into difficulties. The contract should also protect you against theft, fires, and indeed everything covered by a de-luxe insurance policy.

Halsey and Company (0272 503716) are the big fish in the micro maintenance market, with their 'Repaircover' service. They also act as insurance brokers. In theory most brokers can arrange insurance cover for micros, but this is a specialised area and many firms shy away from it.

It may make sense to lease the system, so that you get a replacement on loan if anything goes wrong.

You should consider insurance, and make a few enquiries before you buy your system, as policies and charges vary widely depending upon the equipment you choose. Finally - as ever - check the small print, especially when comparing offers from several brokers.



MULTI-USER MICRO TERMINAL

Would you be good enough to let me know whether or not the Amstrad Word Processor can act as a dumb terminal on a multi-user micro system.
P.J Patel, Wembley, Middlesex.

The Amstrad will work happily as a terminal, but you'll need to buy the CPS interface. This will give you an RS-232 port that can be linked up with just about any multi-user micro. The 8256 display can emulate a DEC VT-52 terminal quite accurately, and most business software can be configured to produce appropriate control codes.

One common problem when linking machines is keeping them in step with one another. There must be some way for each machine to signal that it is 'busy' and can't cope with any more data for the time being, or characters will get lost. You can avoid this on the Amstrad by keeping the transmission speed down to 1200 or - at a pinch - 2400 baud, but this makes the whole system seem a bit lethargic.

There are two common signalling systems, termed 'XON/XOFF' and 'hardware handshaking'. Both allow your system to run at higher speeds - 9600 baud is a common choice. In the first scheme a special character, called XOFF and usually entered as control S, stops the flow of characters and XON, or control R, re-starts communication. Hardware handshaking uses two extra wires between the machines to get the same effect.

A simple terminal emulator is supplied with the PCW 8256 - this is the file MAIL232, which you should find on one of your master disks. You need to buy the CPS interface to find out how to use this. It supports hardware handshaking, which is built into the interface, but not XON/XOFF. If the software at the other end of your link uses XON/XOFF you'll have to use low speeds or discard MAIL232. Several more powerful packages are in the public domain, and most of these support XON/XOFF.

I would warn you that multi-user micro systems tend to perform badly by comparison with independent machines linked in a network. Both are pretty hard to get working properly. I can't be categorical without knowing your intended application and the software you want to use, but I'd recommend that you consider using a network. I don't know of any networking software for the Amstrad at the moment, but I'm sure something will surface soon.



LYNX LINKUP

Can you tell me if a User Group exists for the Camputers Lynx computer? Alternatively, can you tell me where I can get circuit diagrams for the Lynx? Also any information on the disk drive would be nice. I have a fully working Lynx and a never used disk drive with controller chip inside, but no interconnecting interface or software. Have Camputers resurfaced under a different name.
Name withheld by request.

Camputers went bust in 1984. Several companies expressed an interest in buying the business, and in November 1984 a firm called Anston Technology took over. A re-launch was planned but never happened, and in June this year Anston sold everything - hardware, design rights, and thousands of cassettes - to the National Lynx User Group. The group would like to produce a super-Lynx, but at the moment they are busy supplying spares and technical information to owners of existing models.

You can get a full set of circuit diagrams from the Group for £10. A disk controller and interface will cost you £60 - it will work with any standard Shugart drive, but it uses the 'Ready' signal on pin 34, so cheap drives made for the BBC Micro are unlikely to work. You must specify whether you have a Mark 1 or Mark 2 Lynx - the Mark 1 was the model with a 4MHz processor whereas the Mark 2 ran at 6MHz.

Bob Jones runs the User Group - his address is 39, Ashton Close, Needingworth, St. Ives, Cambridgeshire.



FEEDBACK:



RAM UPGRADE UPDATE: William Adams and J.L Holt have written in with further information about the Amstrad 256K memory upgrade which I explained in the August PCW.

Mr. Adams has a 'hybrid' machine with wired links that do not match those described in the original article. His computer contains two rows of three links, labelled C, LK2, and D from left to right across the top row (nearest the memory) and A, LK1 and C across the bottom row. C is connected to LK2 and B to LK1.

As far as I can tell from the original notes supplied by Micro-Bridge, both the present links should be broken and replaced with two new links; one between A and LK2, and the other from C to LK1. I have not been able to check this, because I can't find a hybrid machine to experiment upon.

J.L Holt writes to say that my instructions conflict with those supplied with his Dk'Tronics 256K upgrade kit. Dk'Tronics suggest that only switch A should be adjusted. In fact both instructions are correct - the difference is that my version leaves you with 512K after a soft reset, whereas you get back to a 256K machine if you follow the Dk'Tronics instructions and then reset with SHIFT EXTRA EXIT.



KERMIT STRIKES BACK: Alan Phillips has written in from Lancaster University with further information about the Kermit file transfer system, also mentioned in the August PCW. It seems that although Kermit began life in a micro- to-mainframe application it can link any two machines on which it runs. Kermit is now widely available for micros, although it is still not compatible with Xmodem.

According to Mr. Phillips, "Kermit is vastly superior to Xmodem, and has been implemented on just about every micro with an RS-232 port." To back up this claim he listed over 200 different but compatible versions of the package, all available at cost-price from his University Communications Group. He has offered to field any enquiries from PCW readers, who should write to: Alan Phillips, Communications Group, Dept. of Computing, Lancaster University, Lancaster, England (0524 65201 ext. 4881).


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