Although the Operating System (OS) on the Master microcomputer is excellent, it does have a number of irritating bugs and omissions. This is where MOS+ from DABS Press comes in, for it fixes these bugs in OS version 3.10, and adds some very useful additional commands.

It comes in the form of a sideways ROM, and can be supplied either as a ROM, or on disc for loading into sideways RAM. An eleven page A5 instruction manual details its various facilities. After installing MOS+, the sign-on message produced by the computer changes from "Acorn MOS" to "Acorn MOS+" to let you know that everything is OK.

A number of enhancements have been made to some of the star commands, with quite a few of them as found on the Master Compact. Both APPEND and BUILD will now accept all 256 ASCII characters, rather than the first 128 as before. When loading data into sideways RAM, using either SRLOAD or SRWRITE, an optional "I" parameter can be added to initialise the data. For SRLOAD, this removes the need to press Ctrl-Break before an image is recognised by the Operating System. *UNPLUG can also have this parameter added, in which case the ROM is unplugged immediately, by removing its entry from the ROM information table.

*SHOW has been tidied up so that omitting a key number will cause all the key definitions to be displayed. For *STATUS, the entries are now displayed in alphabetical order, and *ROMS lists Sideways RAM as "RAM", and doesn't duplicate entries.

To backup discs, you don't have to search for the Welcome Disc, as MOS Plus comes complete with the necessary code. *BACKUP automatically handles both DFS or ADFS formats, and if required can use sideways RAM to speed up the process. You can also use it to backup (on DFS discs) from side :0 to :2 (or :1 to :3) on separate discs - it automatically prompts you to change discs.

The *BASIC @ command has been extended so that the tokeniser will accept text from any location, and not just from the EDIT's buffer.

Nine new star commands have been added. For ADFS users, *DRIVE has been added to allow DFS software using this command to still work under the ADFS; *CATALL will catalogue all the files on the disc; EXALL is similar to CATALL, but performs *EX on all files; *FIND will search for a specified file (with wild cards allowed) and display their path if found. A formatter and verifier are also included.

A command called *SETTIME can be used to set the date or time or both of them. The syntax is identical to Basic's TIME$ command. This will allow the RTC to be modified within other languages that do not support it, eg Comal. To complement the sideways RAM handling commands, *SRKILL will clear out the first sixteen bytes of one or more RAM banks.

Part of the 146818 Real Time Clock contains an Alarm Clock facility, which is unfortunately not implemented by the Operating System. MOS Plus allows you to use this, provided you make a link on the main circuit board.

*ALARM is used to control the system. If followed by no parameters, the current setting will be displayed. The alarm can be configured to go off every second, minute, hour, or at a specific time. When the alarm is triggered, a beeping noise is made. Its volume can be adjusted to either low or high, and can be set permanently in the CMOS RAM, if required. For machine code users, the alarm can be trapped by intercepting user event number 9.

To avoid having to install a ROM such as AMX, etc., MOS Plus comes with the mouse driving code necessary, along with the OSWORD &64 call to access it.

With OS 3.10 there were a couple of bugs which could occasionally cause problems. The infamous CLOSE#0 bug, where the DFS does not close files with the correct length in the event of *CLOSE or CLOSE#0, has now been fixed; after *EDIT there can be any number of spaces before the filename; if more than one filename is specified after *REMOVE, the call will correctly fail.

When re-setting the CMOS RAM with R/power-on-reset, the settings now default to sensible values.

A series of help texts can be obtained about MOS Plus itself, the Alarm facility, Basic, View, and Terminal. This is an excellent aide-memoire.

MOS Plus is an excellent product. It offers all those facilities which you are likely to use without having to resort to the Welcome Disc, and a few others that are most useful. It has been well thought out and is a most welcome addition inside any Master.