A&B Computing1st June 1985
Published in A&B Computing 2.06
Cumana's new Electron disc drive interface in action
Cumana Disc Drive Interface
At long last, there are companies out there in the wide blue yonder that actually believe that there is a serious Electron user or two. So far, we have experienced a multitude of joystick interfaces for those who want to play games, several printer interfaces to allow the semi-serious user to see his efforts in print, but to date there has been little in the way of disc interfaces for he who wants fast access to programs and data alike. Well, you lucky people, in the last weeks, two disc interfaces have been announced and are soon to be readily available.
The first of these is the Plus 3 from Acorn themselves: this is a member of the 'Plus' family to go with the Plus 1. The second of the pair is from Cumama. Elsewhere in this month's A&B there is a review of the Plus 3; herein, I look at Cumana's first contribution to the world of the Electron.
Cumana have a long, reliable history in the marketing of disc drives for the BBC. Their reputation goes before them and so their entry into the Electron field must be seen as a big plus (!) for the Electron user.
The Cumana Floppy Disc system for the Electron consists of a plug-in cartridge, which has the disc interface hardware and software, a duel or single disc drive with mains power supply, the essential utilities disc and a manual.
Cumama have said that the cartridge and the utilities disc may be supplied separately from the disc drives. However, no positive indication is made in the manual as to which of the Cumana drives are suitable for the Electron and this interface. Since the basic system that Cumana provides includes a disc drive with a mains power supply, I suspect that the range of Cumana drives without a power supply are unsuitable. However, the rest of the range with external power units are presumably satisfactory.
The cartridge that Cumana have produced is a strange-looking object which is designed to plug into one of the ROM cartridge slots of the Plus 1. The cartridge has a slot for the disc drive's cable to be firmly fixed and next to this are the "fingers" that connect into the Plus 1. I found both the insertion of the drive cable into the cartridge and then the cartridge into the Plus 1 a lot of hard work and semi-panic set in that I might damage something if I pressed the wrong thing too hard at the wrong time. Luckily (or maybe by design) no mishaps occurred and the final product of my efforts was soon laying in front of me.
The minimum configuration, therefore, that is necessary to run a Cumana disc system is the Electron, the Plus 1, the Cumana cartridge and last, but not least, a disc drive.
In producing the Plus 3, Acorn have been very particular to produce a well-designed, compact disc system that both looks and performs well. From the point of view of aesthetics, the Cumana cartridge, on the other hand, is not very elegant. It stands some three or four inches over and above the Plus 1 cartridge slot. This, combined with its arrow width of approximately an inch led me to feel nervous about knocking it. I thought that maybe the fingers into the cartridge slot might bend and damage. However, to date, I've had to mishaps... yet.
Inside The Cartridge
After the initial impressions of the cartridge have been formed, a closer look at it will show something with I think is unusual in home computer peripherals.
At the back of the cartridge, visible to the outside world, there is a cut-out with what turns out to be a battery. This battery provides the power to allow a continous clock to be kept running, even when power is switched off. But even more important is that the disc filing system is stored in the cartridge... yes, in the cartridge, and the big bonus that this provides is that no user RAM is taken up when there are discs in use with the system. Without delving too deeply into this subject, it will mean that tape-based programs may be run from disc without modification and withou the dreaded "downloading" exercise needing to be performed. And all transferrable tape software will run, irrespective of length.
As if this feature might not be enough, Cumana have also included an extra ROM socket in the cartridge. By undoing the four Philips screws in the front of the unit, the insides of the cartridge are exposed. A neat arrangement of chips comes to light with an empty socket waiting for the user's firmware. I immediately tried out a View ROM that was made for the BBC, and to my delight virtually all of the commands work. Living proof of the functionality of both the View ROM and the ROM socket in the cartridge is proved by this article - it was written using them! Of course, the slot that the cartridge takes up reduces the number of Plus 1 slots available to the user and in effect a Plus 1 slot is replaced by a ROM socket.
I do have three worries with the design of the Cumana cartridge however. Firstly, it is the concern expressed earlier about its height, above the level of the keyboard. Secondly, the battery will one day run out and need to be replaced. Whilst it is true that a message has been designed to appear before the user revealing that the battery needs replacing, my concern lies with getting it replaced. At the moment Cumana provide a service which will look after this small problem. But should anything happen to Cumana (heaven forbid!) or should Cumana for reasons known to themselves decide not to provide the service any more, then the Electron owner will have to depend on a third party to do the job for him. Maybe this is not a problem, but certainly worth thinking about.
My third concern lies with the lack of firmware available for the Electron. It's all very well taking a Plus 1 slot and providing a ROM socket in its place. But what do we have to put in it? To date there are only a handful of ROMs specifically for the Electron and no doubt there are several for the BBC (like View) that work well on the Electron, but still nowhere near enough.
The Disc Drives
Unfortunately, I am uncertain as to the range of drives with which the Cumana cartridge is designed to work. I had access to a Cumana CS400 for this review and it worked a treat. The CS400 is an 80 track double-sided 5.25" drive with a possible 400K storage. The drive has a 40/80 switch at the side to allow both 40 and 80 track discs to be used. The Cumana drives have been reviewed many times in many magazines, so I do not propose to look any further at the drive itself.
The Disc Filing System
As mentioned above, the disc filing system is resident in the cartridge itself and is used in such a way as to not impinge on user RAM in any way.
The DFS is in many ways similar to that provided for the BBC by Acorn. However it doesn't seem to suffer the same limitations as regards directory entries. The Cumana manual doesn't say that there are any limitations on the number of entries allowed in the root directory ($) which is set up on formatting the disc. I have put 70 entries into the directory and have had no problems. In practice this number would normally be perfectly sufficient.
What is a sadder limitation to Cumana's DFS (shared by the Acorn DFS, but not by the Plus 3 ADFS) is that there is no hierarchical structure to the filing system. That is, that there is no creation of directories within directories, hence allowing sub-discs to be set up. This is certainly surmountable by judicious choice of filenames and some astute programming, but after having used Acorn's ADFS, this particular deficiency is irritating. It is true that various different directories from $ may be set up, but it is always to just one level of depth.
The DFS Commands And Utilities Disc
The Cumana Disc Filing System has 26 filing system commands. There are, of course, those that are essential to any DFS, such as *LOAD, *SAVE, *DELETE, etc. There are others that are not always found in differing DFSs, such as *DATE (to access the system's date) and *PBOOT (to print out the boot option set by the *BOOT command). I found the commands represented in the Cumana DFS to be perfectly sufficient for the everyday manipulation of files.
With the cartridge came a utilities disc (or diskette as the manual refers to it). This disc had on it some very interesting aids to the disc user. Of course, there were the usual bunch of BACKUP, COPY, FORMAT and VERIFY, all essential, but the others interested me. There was a set of transfer utilities for the transfer of programs from one DFS format to another. Those provided are:
Cumana Double Density to Acorn Single Density
Acorn Single Density to Cumana Double Density
Acorn ADFS to Cumama Double Density
What this means is that any disc software provided for the Acorn DFS may be transferred to a disc for use with the Cumana system. So any BBC software, as long as it is not protected, may be at least tried on the Electron. Similarly software produced for the Plus 3 may be transferred using A<TO<D.
One of the other utilities available on the disc is one for formatting an Acorn Single Density disc. Used in conjunction with D<TO<S, this ensures that software may be transferred from Cumana format by Acorn Single Density format.
I used the S<TO<D utility to transfer some utility software that had been written for the BBC. The resulting disc, in Cumana Double Density format, worked well, there being no problems with the conversion. Unfortunately, the software had been written in Mode 7 and proved to be unsuitable for my use on the Electron. I will be using the D<TO<S utility to transfer this word-processed article to an 80 track Acorn single density formatted disc, so that it may be used as direct input into the new type setting facilities now being used at A&B. Fingers crossed. [It worked! - Ed]
So, using various combinations of the above utilities, the user may transfer programs to and from Acorn Single Density, ADFS and Cumana Double Density formatted discs. Very, very useful.
Other goodies on the disc are a DISK<EDIT (allowing direct editing of the disc, only recommended for the more advanced user), SET<TIME (which allows easy amendment of the cartridge-maintained date) and the aforementioned SFORMAT and SVERIFY (allowing formatting and verification of Acorn Single Density discs). All of the utilities on the utilities disc provided are accessible from an auto-booted menu, so making their use that much easier.
An interesting pair of omissions from the list of utilities provided are *COMPACT and *BADSECTOR equivalents. Whilst I cannot explain the lack of the second facility, a possible reason might be forthcoming with a quick look at the way that the Cumana DFS extends files.
Each file has one sector allocated to it which described the positions of all the other sectors of the file, wherever they may be on disc. The description of each of these position is held in pairs, i.e. the sector number and the sector length. The sector number is the first of a set of contiguous sectors belonging to the file, the last sector in this part of the disc being calculated from the sector number + length-1.
Each sector on disc has a bit assigned which, when set, means that the sector is free; otherwise it is in use. On trying to find space, the DFS attempts to find the first free space on the disc that is big enough to contain the information to be stored. If a file is to be extended, the search for free sectors begins with the sectors immediately following the last sector already assigned to the file. The net result of this is that the contents of a file are not contiguous, even when the file is first created and hence the need (supposedly) for an *COMPACT is not there. However, even if the DFS is clever enough to do this, the access time for both reading and writing must increase if the drive head dots around the disc to get all the relevant information. Personally, I would have liked to have seen an *COMPACT utility included.
Use From Basic And Assembler
The day will come when many who buy an add-on such as Cumana's disc system will want not only to use commercial software, but also to write programs that fully utilise its capabilities. This ADFS fully supports the Electron BASIC random access files, allowing the writing to and the reading from files stored on disc in a non-sequential manner. The idea of having a pointer to the data within a file is maintained and hence it is possible to write more sophisticated programs, such as databases, with more facilities and greater scope.
There are some extra facilities which may be used from assembler. These take the form of the infamous "OS" routines. To name but a few, OSFILE, OSBPUT, OSBGET and OSGBPB are available. The last of these is of particular interest as various values for the A register will allow a multitude of information on the files on disc to become available.
It is essential that with any new peripheral, the documentation on how to set it up, to use it and to maintain it is clear, concise and well-written. The Cumana Disc Drive Guide that comes with the drives is certainly excellent on these points. There are many clear diagams to show how the pieces fit together, as well as short chapter to ensure that boredom does not set in whilst reading it.
However, it must be said that there is a distinct lack of examples in the text and this does lead to some possible confusion, especially in the area of directories. I could find no information on how to create directories or how many entries (if there is a maximum) are allowed in a directory. At the moment I believe that the only way to create a non-$ directory is to rename $.[filename] to [new directory].[filename]... is this so?
The topics covered in the manual start with the theory of 40 and 80 track, following quickly by the handling of discs, drives and the setting up of the cartridge. Chapters 5 and 12 cover the filing system and utilities available, whilst Chapter 13 is a basic lesson in transferring tape software to disc (there is no information in here for would-be pirates!).
The appendices, of which there are five, give some technical information on the way the disc sectoring works as well as a few notes on how Cumana have attempted to minimise the "Can't Extend" file problem, some hints if non-Cumana drives are to be used, the fitting of the additional ROM, replacing the battery and a list of the DFS errors. With an index to round it off, the manual is certainly not a bad little effort running to about 70 pages.
It is always very difficult to assess the advantages and disadvantages that one DFS has when compared to another. The Cumana dis system is certainly a useful package for the Electron owner. With the world of 5.25" discs opened up to him, he must now hope that manufacturers will transfer their products to it. Whilst I am not overjoyed by the cartridge's physical appearance, I cannot ignore the fact that it works well, providing an excellent set of basic facilities to the new disc owner.
I have now seen and used both the Plus 3 and this system. The choice would be very difficult and I'm not about to go one way or the other. The Plus 3 has ADFS, which is better than both the standard Acorn DFS and the Cumana DFS. However, beware. If there is ever any possibilitiy of either upgrading to the BBC or changing to another make of computer, the Plus 3 will be of little use, but the Cumana drives, with the appropriate interface, will still be available interface, will still be available to you. Cumana have certainly scored a great success in designing a system which works and works well, including as an extra bonus the ability to run tape-based software with little, if any amendment.
One thing is now sure. The Electron owner does have a choice and it is up to the software houses to support at least one, and preferably both, of these excellent DFS systems.
The Cumana Disc Interface costs £49.95 or £129.95 if bought in conjunction with a disc drive. Available from dealers or direct from Cumana at The Pines Trading Estate, Broad Street, Guildford, Surrey GU3 3BH. Telephone: (0483) 503121
lock or unlock file
set option to be executed on pressing Break
create command file
show catalogue of files on disc
close any currently open files
display the system date
delete single or number of files
set current drive and directory
change current drive
display a hexadecimal listing of the file with ASCII equivalent
execute files created with *BUILD
show the number of used directory entries and free sectors
give information about the computer and ROM software installed
give information about files on disc
set the library drive and directory
load a file into memory
display file access information and specify auto-boot option
print out boot option set by *BOOT
rename a file
load and execute a file
save a portion of memory
redirect screen text to a nominated file
give the disc a name
display a file as lines of ASCII text