Master 512
Forum by Robin Burton
Beebug Vol. 9 No. 1 May 1990
Like last month's Forum, both topics this month stem directly from readers' letters. I don't know who was the first discoverer of the trick in the second half of the Forum, but it just goes to show what devious minds some 512 users must have!
Before that, though, a reminder of protocol and good manners seems to be about due after recent events.
LETTERS
I'm still getting a reasonable number of requests for 512 BBCBASIC 9 months or so after the original offer (total now around 350). Let me say before continuing that I'm still happy to supply this software free to BEEBUG members, or to answer queries if I'm able, but only if you obey a few simple, reasonable rules. Clearly not everyone has read the relevant back issues to find out what these are!
For anyone intending to write to me or to request a copy of BBCBASIC I'll recap. I hope the rest of you will bear with me for a moment.
I will supply a copy of Richard Russel's special 512 version of BBCBASIC to BEEBUG members free of charge, provided that you observe the conditions of the offer, which are:
| 1. | You must supply a blank 800K formatted 5.25 inch disc. |
| 2. | It's pleasing if you enclose a letter or note to me, but
in all cases you must quote your BEEBUG membership number. I do not provide
this service to non-members, especially after BBC Acorn User's recent invitation
to all and sundry to join in. |
| 3. | You must supply suitable self-addressed return packaging,
complete with adequate postage in the form of stamps or, from overseas,
International Postage reply coupons. |
| 4. | You should clearly address the outside of the package you send for my attention, and if appropriate also mark it '512 BBCBASIC'. |
I apologise to the rest of you for going through all this again, but it is called for after numerous recent requests. That's the list of 'DOs', here are the 'DON'Ts'.
| 1. | DO NOT just address your package to BEEBUG. Anything intended
for me (c/o BEEBUG) or the Forum should be so marked to avoid unnecessary
and time wasting extra handling. |
| 2. | DO NOT include a request for BBCBASIC with any other letter,
order, query or anything else intended for other BEEBUG staff or departments
(unless your letter to me is enclosed separately in its own packaging inside
the first). |
| 3. | DO NOT say 'please debit my Access card/Barclaycard/BEEBUG etc. account with the cost of postage' – it can't be done. You must include suitable postage with your request. |
The reason for these rules is simple – I do not work at BEEBUG's premises. I am not a BEEBUG employee, nor should BEEBUG be involved in providing the service beyond forwarding your letters to me. If you write to BEEBUG – write to BEEBUG, if you write to me – write to me care of BEEBUG. Remember the two things are NOT the same!
As I said some months ago, the vast majority of readers behave perfectly, which makes the job easier for everyone, thank you. However, quite a number of recent requests have caused extra work, extra correspondence and delays by not following these simple rules.
I realise that some of these may have been from readers who hadn't had their 512 very long and hadn't read earlier Forums, but after this issue ignorance is no longer an excuse. If you send me a disc without suitably addressed return post and packaging I shall, from now on, assume it is a gift!
In any case I'm prompted to suggest that, if you are a new convert, either to the 512 or to BEEBUG, you would find it useful and enlightening to read the back issues. 512 Forum has been running now for nearly two years and I try not to repeat previous items if possible (unlike this one unfortunately). If you are a new member and don't have the relevant copies, back issues of BEEBUG can be easily obtained at very reasonable cost. In fact BEEBUG is the only magazine I know where back-issues cost less than new ones! How reasonable can they be?
That's that over with, and I sincerely hope for the last time. Now we can move on to more interesting things.
RUNNING MS-DOS
Yes! the heading is correct! However, you'd better read on before getting too excited. A letter containing the information on this arrived a couple of weeks ago along with a request for 512 BBCBASIC. I therefore take neither credit nor blame for the following and should tell you I haven't tried it, I merely present it in good faith as an item of general interest in more or less the form it was received.
The facts have been publicised on a bulletin board, I don't know which, but before you consider trying it, I must point out that copyright applies to the use of any version of MS-DOS. It might be alright if you personally hold a licence for MS-DOS for your own PC, but in all cases it is your responsibility to check the licence agreement. For most of you the exercise should be regarded as only of academic interest. Even so, I hope you are at least intrigued, as I was. If any of you find you can legally use a copy of MS-DOS here are the steps to take.
The first task is to create a file called 'BOOT.COM', the contents of which are an 'INT 19' instruction. If you have BBCBASIC you can easily do this by using the in-line assembler, or with any other '86 assembler, but I'll explain another way for those of you not happy with either of these methods.
First create the file itself, 'BOOT.COM' by issuing the command line instruction:
COPY CON BOOT.COM
This is the operation you have probably used before to create a batch file. As soon as the command is issued the current drive should start up and DOS will open the named file for output. You can now type text directly into the file, so this is a way of creating the file. Type a few characters into it, at least six in total but anything will do. The characters don't matter because they will be changed in a moment, but six are needed to provide room for the 'INT 19' instruction and a default stack. Finally press Ctrl-Z followed by Return, and the file will be written to and then closed. You can check that it has by issuing a 'DIR'.
Next you need to change the contents of the file using 'EDBIN'. This is the binary editor which is included on issue disc one. To edit the file ensure that EDBIN is available in a current path and load the file for editing. Some of you will know how to use EDBIN, but for the remainder all you need to do is follow the instructions. Assuming drive A: is the current drive containing EDBIN and drive B: contains the file, the command is:
EDBIN B:BOOT.COM
EDBIN will execute and confirm that the file is loaded by showing the byte count, followed by the prompt, which appears as a hyphen '-'. If you now enter an 'H' (for help) and press Return you will see all the EDBIN commands displayed. After you've read this enter an 'E' and press Return so that you can edit the contents of the file.
Your cursor should be under the first hex byte in the file, which is to be changed to 'CD'. This is done by entering first the 'C' then the 'D', because you'll notice that bytes move in from the right as you enter them, pushing the previous contents to the left. You'll also notice that after entry, the cursor doesn't move on to the next byte automatically, you must do this yourself using the cursor right key. In the second byte, the required value is '19', so enter these two digits.
The remaining four bytes of the file should contain hex zeros; if they don't, amend them. When you've finished, leave edit-mode by pressing 'Ctrl-C'. All that now remains is to rewrite the file, which is done by entering a 'W' followed by Return. No filename is needed, as EDBIN uses the original name by default. You can now leave EDBIN by entering a 'Q', at which point pressing Return will take you back to the command line.
THE BOOT DISC
The next requirement is to get hold of the copy of MS-DOS or PC-DOS that you intend to try out. This is best achieved by using your PC to prepare a new system disc by formatting it with the '\S' suffix. Again assuming drive A: is to be used for your floppy the command is:
FORMAT A: \S
This is a similar operation to producing a bootable 640K disc in the 512's 'DISK' command. The disc is first formatted, then at the end the system files (i.e. the operating system) are copied onto it.
Back on the 512 again, copy the BOOT.COM file created earlier onto the new system disc. You're now almost ready to experiment, but before you do, a couple of points for those to whom they may apply. Remember when you're treading new ground, just like trying out any new software, you can minimise risks by a couple of sensible precautions.
If you normally have any special settings, or resident utilities loaded automatically by an AUTOEXEC.BAT file it's best to reboot the 512 and run it 'bare' for this exercise. Equally, if you normally run your 512 from a Winchester it's also good advice to switch the Winchester off and boot and test from floppies until you are sure this works with no ill-effects.
After observing the warnings, all you need to do is to insert your newly created MS-DOS disc into the default drive and type:
BOOT
followed as usual by Return. The chosen version of MS-DOS should then start up successfully, indicated by a return to the familiar 'A>' prompt.
LIMITATIONS
As usual you don't get anything for nothing; what you're doing is running the MS-DOS kernel within DOS Plus, so both occupy their normal amount of memory. As my correspondent pointed out, you'd only have about 260K free in an unexpanded 512 (90K less than usual) so it isn't much use for running software.
What it might be useful for though, is installing software which normally can't be configured on the 512, but which does run once this process is complete (installation must be done under MS-DOS for some packages). If you have an expanded 512 the reduced memory won't be a problem, of course, so you may even find a few programs can be set up which don't normally run at all. Others that normally run with limitations may perform more correctly with MS-DOS running during installation, particularly if it's a later version than 2.1.
I understand that MS-DOS version 3.2 works, but only from DOS Plus 1.2, while PC-DOS 3.2 doesn't work at all. The bulletin board which originally contained the information also said that both MS and PC-DOS 2.0 work, but I can't add any comment to this.
Next month I'll include more information on some of the packages that have been tried.