PC Ditto

Reviewed by Patrick Owen


Issue 32

Mar/Apr 88

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Can your ST really behave like a PC? Patrick Owen tests out Robtek's new IBM emulator which at 89.95 is a lot cheaper than buying a second computer!

PC Ditto turns your Atari ST into an IBM PC Clone. It works on the 520 or 1040 with either Colour or Mono screen and 3.5" and 5.25" diskettes as well as hard disks.

The documentation provided with it (on disk) lists over 300 pieces of PC software which have been certified as running under PC Ditto. I tested a few myself on my 520ST with a colour monitor and both Atari and Triangle drives and found nothing that would not work. Very impressive.

But ... everything I tried ran at around quarter the speed of a PC. The distributors, Robtek, claim that it runs at around 80% of a PC. I tried Lotus 1-2-3 (Version 2.01 3.5" version), IBM DisplayWrite Assistant (Version 1.5 3.5" version) and a few games Dragonworld, Mean 18, Calixto Island, Rogue and The Leather Goddesses of Phobos under both PC DOS 3.2 and PC DOS 2.1. The text in Calixto Island and Dragonworld scrolled up quite quickly (half speed?), but whenever it had to display graphics it slowed down significantly, and the music on Dragonworld came out at less than a third of the normal speed a very strange effect. All of my other tests (e.g. loading 200 records into 1-2-3 and sorting them, paging up and down in the word processor, and issuing multiple commands in LGoP) ran around 3 to 7 times slower under PC Ditto.

In case I had either faulty software or problems with my hardware I tried a friend's 1040ST with the same results and also got a new copy of PC Ditto from Robtek. The new copy did have about half a dozen bytes different in one program file, but had no effect at all on the response times. Robtek say they have 5,000 happy users either I am doing something wrong, or those users don't realise how fast a PC should go I do because I have an IBM PC sitting beside my ST!

Of course speed is not necessarily critical. If you are running a program which gives sub-second responses then under PC Ditto it may well still be fast enough to use. If you want compatibility with your office machine on a casual basis you may be more interested in the fact that it works than how fast it is.

Apart from the performance there are a few other limitations. First, it won't run IBM BASIC(A). This is a common limitation with PC Clones, caused by the fact that a large part of the BASIC is in microcode in the ROM on the PC System Board and is copyrighted by IBM. I seem to remember hearing that there were versions of BASIC around that could bypass that problem if it is important to you then contact your local IBM Dealer. Secondly, PC Ditto will only run software configured for an IBM PC rather than a Clone. This of course raises the basic question of what exactly is compatibility!

No machine is 100% compatible. Amstrad, for instance, do not even claim compatibility they say they can "run all the famous IBM software". IBM has a wide range of machines which are not fully compatible, e.g. a 3270-PC screen has no intensity attribute bit so you only get 8 colours in text mode instead of 16.

IBM published a set of extremely extensive Technical Reference Manuals for the PC and PC DOS. These more than anything accounted for the success of the PC. They allowed more people than ever before to produce compatible hardware and software. So what is meant by 'compatibility' is not that the machine should be 100% identical, but that it should conform to the interfaces described in the manuals.

Unfortunately technology moves on and some of the standards are now either inadequate or obsolete. IBM itself no longer sells 'PCs' the new range is called the Personal System 2, though it is of course 'PC Compatible'. The main problem areas are threefold: the keyboard, the screen, and the disk drives.

On the keyboard side PC Ditto does very well the Atari ST has lots of keys and only a few mappings are required, these are documented on a template. Two minor problems: the backslash, hash, tilde and broken vertical bar keys are all mixed up and there is no audio feedback, i.e. no click of any kind when you successfully depress a key.

The screen is pretty good, but here is where we find a number of undocumented limitations. Blinking, underlining and highlighting are not fully supported. In Medium Res Colour PC Ditto only supports 4 colours in text mode and in Mono High Res only 2. A PC Colour Screen has 8 plus intensity making 16. In order to see what I was outlining for Block Commands in DisplayWrite Assistant I had to get it to emulate a PC Mono Screen on my ST Colour Screen at least it did work then!

What about disk drives? Virtually all PC software these days is provided on double-sided diskettes (both 5.25" and 3.5"). PC Ditto recommends "If you are not technically experienced and can not obtain technical assistance, we recommend that you purchase a double-sided drive. The cost of the drive will most likely be worth avoiding the technical frustrations you will encounter." I wholeheartedly endorse this. Whether you choose 5.25" or 3.5" is up to you. But without a double-sided drive no amount of technical experience will enable you to load a protected program such as Lotus 1-2-3 which only comes on double-sided diskettes!

One other area which can affect your ability to run a program under PC Ditto is the memory. My 520ST has 364K left for PC use. The documentation says a 1040 will have 703K (but PC DOS will probably limit you to 640K anyway!).

In conclusion, I would recommend that if there is some particular PC software which you want to run on your ST, you should check before buying PC Ditto that what you want will a) load on your hardware, b) not use colours or highlighting which make it unusable and c) run fast enough for your needs.

For those interested in other ways of achieving IBM PC compatibility the following may be of interest. If your PC has a 3.5" drive then, as long as you format your diskettes on the PC, you can transfer flat ASCII files between the machines with no problems (at least I have had none so far!). You will need DOS 3.2 to format the 3.5" diskettes and if your Atari ST has only a single-sided drive you will need to use a command such as DEVICE = DRIVER.SYS /D:2 /H:1 in your CONFIG.SYS to configure a single-sided drive on your PC 3.5" drive. If you want even more power and PC ability you may wish to investigate Alfa Electronics Ltd (01-390-2588) for 239 they will provide you with their Supercharger (8086 processor, 1MB RAM, etc.) to plug into the back of your ST!