PMS 64 kB SRAM storage drive

Software that’s boxing clever

The following review by Mike Cook was posted to the January 1986 edition of the British magazine The Micro User (pp. 57–8):

The original specification for the BBC Micro had provision for paged memory to be attached to the 1MHz bus, but until now no one had produced a device.

However Permanent Memory Systems has come up with the goods in the form of a non-volatile RAM module. Non-volatile means it will remember what has been put into it even when the computer is powered down or the module is disconnected.

This system is not to be confused with any sideways system that utilises 16k banked switched memory nor the so-called shadow systems.

The module is a small box 3½in by 5½in by 1¼in with 9in of ribbon cable and a plug for the auxiliary power socket. Options include a smart black carrying case and lead to allow the module and disc to be plugged into the auxiliary power socket.

Electronically the system consists of 64k of static RAM with battery backup. The computer sees it as 256 bytes of memory in page &FD with any one of 256 banks being selected by a memory location in page &FC.

Described like this you might think that it is not exactly the most interesting add-on currently available, but you would be wrong. You see, what makes this shine is the remarkable software – second processor compatible – that transforms this box into many useful configurations.

The first and perhaps the most potentially useful is the software that makes the module work like a disc.

I am sure that those of you with discs have experienced the frustration of arriving to demonstrate your latest piece of whizz bang software only to find your friend’s system does not have a disc drive.

Or have you used an Econet system at school and then wanted to take your program home and found no separate disc drives are available?

Well, the ROS will be the answer. ROS stands for Ram Operating System and it allows the PMS RAM module to act just like a disc drive, storing and retrieving programs.

You can unplug the module and take it to another computer and run your programs even if it has no disc interface fitted.

As if this were not enough, access to this pseudo disc is many times faster than to a real one. This speeds up programs that access disc files.

Having taught students to work with disc data files I suspect the module will considerably save on the wear and tear of disc and media during the normal “run, file open and crash” sequence they are locked in for many weeks.

All the disc features are available without re-setting PAGE as the system uses the cassette operating system’s BPUT buffer. However should you wish, this is relocatable when the system is initialised.

On the whole ROS commands work just like the disc variety. The most notable exception to this is *DELETE which just marks a file as deleted.

It will continue to show in the catalogue but with a D to indicate it is deleted. The space occupied by the file will only be released with a *RCOMPACT command.

The software supplied with the module contains other DISC/ROS programs, including one to transfer files directly from one filing system to the other.

Unfortunately the only disc system it will work with completely is the Acorn DFS. It refused to work with my Watford DFS and even crashed when the Watford DFS was fitted but the Acorn system was active.

However it was not so serious as I could transfer programs by loading them from disc, switching to the ROS and saving them to the module. I am told that the software is continuously under review, and users will be able to get the new updates for the cost of a disc and postage.

There are also programs to test out the module’s memory as well as to transfer the whole module’s contents to a large disc file, which can then be loaded back from disc into the module.

The PMS module doesn’t stop at providing an alternative filing system, though. For a start there is a program to convert it into a 64k printer buffer so that you can get down to writing the next review while your last one is printing out.

And have you ever been working in a word processor and wanted to check something out in a spreadsheet? Well, with the PMS module you can dump the whole of the computer’s memory and run your spreadsheet.

When you have finished the memory can be reloaded and you will be back in the wordprocessor exactly where you left off.

Another utility allows single disc owners to back up a 40 track disc with only two swaps without corrupting any Basic program in the computer.

The module has great potential for developing programs with dynamic overlays. That is, writing the program in sections and only loading the section currently needed into the computer.

In this way very large programs may be squeezed into a small system.

There is a utility to help this that allows Basic functions and procedures to be resident in the module and pulled in automatically when needed. You can do this with discs, but the time taken for swapping data is very long in comparison with this module.

All in all, a most interesting development. However, I did have some difficulties with the system.

I have already mentioned the fact that only the Acorn DFS is currently supported. In addition, there are no wild cards characters in the ROS commands.

These were lost because of a trade-off between performance and useable memory space. With the ROS installed in the module there is just over 59k left to store your files.

Another problem occurred when entering the ROS: I found that all the strings in the user definable function keys were lost.

I was told this was done to prevent an error if the Break key has been re-programmed. By omitting a line in the initialisation program the function keys are not cleared.

Verdict: All in all this is a gem, albeit flawed. But the flaws are certainly worth living with. This unit will become standard in schools, and is a must for people who want the ultimate in media portability.