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5 : DOS Plus Commands        


One of the potentially confusing areas of using PC software concerns the close similarities, but minor differences between MS-DOS, DOS Plus, and DOS Plus as supplied with the Master 512. This is especially so if you use other PC machines, perhaps at work, and a Master 512 at home.

Transient Commands

The first point to appreciate is that not all DOS Plus commands are permanently resident in the Operating System. This means that some of them must be loaded from disc every time that they are required. These commands are in effect specialised utilities which extend the Operating System, but are held on disc so as not to permanently consume memory. Generally they are called transient commands, since they exist only at the time they are in use. If they are called twice in succession, they are loaded twice. (Of course you may have a RAM disc, so they might not actually be loaded from a physical drive.)

All the standard Master 512 DOS Plus utilities and transient commands are provided on DISC 1. You should make a copy of this disc to be used as your working 'boot' disc, while retaining your original as a safe write-protected backup. You may, in addition, find it helpful to copy some of the more commonly used transient commands to your working applications or data discs. It is possible that some applications may assume the presence of these commands, or you may wish to use them yourself.

For example, you might wish to change the access permissions of a file to read-write, to allow updating. After use you might reset the file to read-only again for safety. Both operations require the use of the FSET command, which is a transient, hence it must be on a current disc at the time the command is issued. Copying the file FSET.CMD to your applications disc is all that is required in this case. This would avoid the need to swap discs when file access permissions are to be changed.

The usual method of keeping these files separate from your applications software or data files is to set up a directory to contain only these files. Commonly, the directory name used is DOS. If you also use the PATH command (see Chapter Three) to set this as the directory to be searched for any files not contained in any current directory (this works like the library directory in ADFS) DOS Plus will ensure that all transient command calls are actioned without further explicit reference to this directory.

One special command which is a transient, but is loaded by default and therefore is usually 'transparent' (ie it is not usually explicitly called by the user) and can largely be treated as permanent, is COMMAND. This is the program which interprets keyboard command entries and can be regarded as responsible for calling and running other commands. You may occasionally find that, after running an application that requires all the memory, exiting the application causes immediate access to the disc. If the system disc has been removed in favour of an application disc, and your application disc does not also contain the file, you will receive the message:

Cannot load command.com

DOS has allowed part of the area previously occupied by COMMAND.COM to be overwritten so as to free more memory for your application. Within the application the processing of keyboard input is under the control of the application itself, so COMMAND.COM is not needed. However, on attempting to return to the normal input prompt, DOS can now no longer interpret commands until a disc is inserted containing COMMAND.COM, which must be reloaded before work can resume. If you encounter this situation you should place a suitable disc in the current drive and simply press return, which causes DOS to retry the load. When successful the standard prompt re-appears and normal processing of commands can resume.

There is one other occasion when COMMAND.COM, or its absence, may make itself known, and again it is concerned with running applications. Many applications permit a temporary exit to DOS, allowing normal commands to be issued from the normal prompt while the application is still active. The usual method of returning to the application is to enter the EXIT command.

Two possible situations can interfere with this facility. The simplest is that COMMAND.COM is not present on the disc, when the application should tidily handle the event by reporting a controlled error, displaying a message similar to the DOS message above before continuing. This problem is easily solved by ensuring that COMMAND.COM is available when required. The second situation is more of a problem, and that is when COMMAND.COM is present but there simply is not enough memory to load it concurrently with the application. In this case the message will be clear and the situation should again be controlled, but unless you are able to free some memory this facility must remain unavailable with the application in question.

Command Compatibility

It should be noted that some commands, or their precise actions, are either unique to the Master 512 or are familiar DOS commands altered in function because of the special architecture of the co-processor. Wherever possible, due regard has been taken of the differences between the Master 512 and 'true PCs', and you will find that certain commands are included only for application compatibility. This allows packages that call these utilities to do so without crashing (exiting unexpectedly) even though the command may have a modified function, or none at all, on the Master 512.

Specialised Facilities

Some commands are written so they may be called either with or without parameters. Depending on the nature of the command one of two types of action usually results. For commands like ADDMEM, BACKG or SLICE, the current setting will be displayed if no parameters are supplied and the command terminates. Others, for example TIME, will display the current setting then prompt for a replacement value, which may be entered in the usual format, or omitted by pressing RETURN, when the existing value remains unchanged.

Yet another possibility is the action of commands like STAR or PIP, both transients, but both of which also may be called without parameters. These can then be used repeatedly without the need to reload. For example if STAR is loaded without parameters the A> prompt is replaced by a * prompt and a star command may be supplied, followed by RETURN, as many times as required. Each star command is executed, then the * prompt returns. To exit press RETURN without supplying any further data, when STAR terminates and the A> prompt reappears.

Command Conventions

The next few chapters describe all the standard system and DOS Plus commands provided in Acorn Master 512 implementations of DOS Plus. You should note that there are both deletions and additions in the latest release of the software, DOS Plus 2.1, when compared with earlier issues. See the page opposite for details of obtaining an upgrade to DOS Plus 2.1. The syntax of each command is given in the following chapters using the following standards to indicate parameters or variables:

DIR       A directory attribute. Where this is shown the entry of a directory name is implied. <This is wrong. In directory listings <DIR> may indeed be used to mark a directory. Otherwise, in DOS Plus, the DIR attribute means a file can be listed with a normal DIR command. It is the opposite of SYS (see below). This applies particularly to the FSET and SDIR commands – YP>
<n>   A variable decimal number must be supplied.
<opt>   Indicates that options can be supplied.
[ ]   Option delimiters, when supplied to a command the entered options are enclosed in square braces.
( )   The range of options is shown within round braces.
RO   A file read-only attribute.
RW   Read-write attribute
<s>   A variable character string
SYS   A system file attribute. Some commands accept /S to indicate this.
{ }   An optional entry. The braces are not entered, but the enclosed item(s) can be, if required.
...   The previous item shown can be repeated as necessary.
|   Shows alternative mutually exclusive entries, which may or may not be optional.
^ or CTRL   The CONTROL key
*   The 'rest of field' wildcard
?   The single character wildcard

The format used to explain each command first gives the name as entered when calling the command. Next is shown the full syntax of the command, using the above conventions as required. This is followed by the minimum abbreviation (if any) by which the system will recognise the command. In practice very few commands can be abbreviated, and never any of the transients. If a default value applies to the command this is shown next.

Any such default is the status, setting or value automatically adopted by the system on initial load. In general this will be replaced by a value supplied with the latest use of the command. Some such commands may be entered without parameters, when they will display the current setting. The versions entry shows the versions of 512 DOS Plus with which the command was issued. Three versions have been released by Acorn, 1.2, 1.2a and the current 2.1. DOS Plus as supplied by Solidisk with the PC Plus is effectively 1.2a, but see also below for 2.1.

The standard Digital Research command name is shown next, followed by the equivalent MS-DOS command when applicable. Where 'None' is shown for both entries the command is specific to the Master 512, and is necessary because of the hardware in either the 512 or the BBC host. If a Digital Research equivalent is shown, but 'None' is shown for MS-DOS, this indicates that the command is a DOS Plus command only. DOS Plus has two features that are not present in MS-DOS, namely limited multi-tasking and CP/M86 compatibility. Such commands are mainly concerned with these features.

Examples of use are then shown, with an explanation of the action of the example. This is followed by any relevant messages, or message types, likely to be output as a result of using the command. Where applicable, notes are included to add further comment or explanation. The final item 'See also' only appears where two or more commands are similar or related, in which case the other commands are cross referenced.

DOS Plus Version Upgrade

If you are using an earlier release than DOS Plus 2.1 you can obtain an upgrade for just £15.00 by sending your original system disc – DISC 1 – directly to Acorn.

As well as containing a number of additional facilities and commands over earlier versions, release 2.1 has all known bugs fixed. Solidisk PC Plus owners should note that no amendment is required to version 2.1 to allow for the memory expansion, as the memory map is already modified to cater for this.

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