The Messenger System:
'The Messenger' was Samco's ultimate answer to spectrum compatibility. It consisted of an interface which plugged into the edge connector on the back of the _spectrum_ and from this a cable ran to the SAM's network port. There was also a very small card which plugged into the SAM's EuroConnector and had a single button on it which generated an NMI. The third part was a disk that had the Messenger program itself on it.
Basically operation worked like this:
When you first bought the messenger you transfered the Spectrum's rom down the network cable and stored it on the Messenger disk.
From then on, to get a new game onto the SAM you loaded the Messenger disk into the SAM and loaded the game that you wanted into the Spectrum from tape in the usual way.
Once the game was loaded into the Spectrum you pressed the button on the back of the Messenger interface (which is plugged into the Spectrum remember), and this 'froze' the machine at that point.
You then had a number of options that you could select from a menu on the SAM:
Selecting "Recieve Program" transfered whatever was running on the Spectrum down the network cable onto the SAM and you could then run it on the SAM and/or save it to disk.
If you had a Spectrum program running on the SAM then the NMI card allowed you to exit it and return to the Messenger menu.
In future, whenever you wanted to play the same game all you needed to do was load in the Messenger software and then load the game from a SAM disk, very much faster than waiting for a tape!
Further features of the Messenger:
Program transfer worked both ways - you could download a program from the SAM onto the Spectrum where it would run quite happily. This was useful as there are some Spectrum games where you simply have to save to tape occasionally.
As well as transfering complete programs you could also send and recieve screenshots from the Spectrum in SCREEN$ format.
As I implied above the Messenger allowed you to download the Spectrum's ROM to the SAM.
Finally, if you simply loaded the Messenger disk and selected the 'Run Program' option without first loading a game then you got the familiar '(c) 1982 Sinclair Research' and had all the fun features of Sinclair BASIC to play with.
Early versions of the Messenger interfaces were supplied by MGT/SAMCo without cases around the circuit boards. The model I bought had a case of the Spectrum side (a bog standard Kempston joystick interface box with a hole cut in the back for the interupt button and an MGT type sticker over the hole where the joystick usual went. (it looked professional!)). The NMI card which went into the back of the SAM had no box, but it didn't need one as it was a piece of PCB mounting a spring loaded switch.
Overall there must have been 95%+ Spectrum compatibility, and even those games that did not run perfectly were usually playable. The NMI card allowed you to interrupt play and snapshot to disk at will so you could save moments of glory or start the game from level 5 each time if you liked.
The Messenger was easily far and away the best method of getting Spectrum compatibility for the SAM.