The Computer Journal, Issue 32

Z-System Corner

© Jay Sage

Reproduced with permission of author and publisher.

As usual, I find myself with the deadline for this TCJ column fast approaching, wondering how two months have passed so quickly. And, as usual, I have far more material that I would like to talk about than I will have time to put down on paper (or, should I say, disk). This column is probably going to be shorter than average, just as the previous one was much longer, and some of the promised discussions will be deferred still further. Given the reasons, you will be understanding I hope: Joe Wright and I are in the process of putting the final touches on the new releases of ZCOM and ZCPR34! By the time you read this, they will definitely be available. Even if you usually find my columns a bit too technical for your tastes, I hope you will read on as I describe these two exciting developments.

I will not describe it here this time, but Bridger Mitchell has very nearly completed code similar to NZCOM that will run on CP/M-Plus systems. At last people with newer CP/M machines for which CP/M 2.2 is not available will also be able to run Z System. And they will be able to do it while retaining almost all of the good features of CP/M-Plus!

The New ZCOM

Two issues ago (TCJ #30) I described the status of the nascent NZCOM. Things have developed considerably since then, and I can now provide some specific details.

First some philosophical comments. This may sound rather strong, but Joe and I both firmly believe that NZCOM is one of the most exciting and remarkable developments in the history of microcomputer operating systems. With all the computers we have had experience with, the operating system has been a static entity. You 'boot' up the computer, and there you have the operating system, fixed and immutable. Few computers offer more than one operating system. With those that do, the only way you can get a different operating system is to 'reboot', which generally involves inserting a new boot diskette and pressing the reset button. And never do you get to define the characteristics of that operating system. You just take what the manufacturer deigns to let you use.

With NZCOM the operating system becomes a flexible tool just like an application program. You can change operating systems at any time, even right in the middle of a multiple command line sequence. You can do it manually, or alias scripts can do it automatically, in response to conditions in the system! And you can determine which Z System features are supported.

You can change the whole operating system or just a part of it. Would you like a new command processor? No problem. With a simple command, NZCOM will load it. No assembly or configuration required. One file fits all! That new CCP will continue to run until you load another one. Want to experiment with a new disk operating system (we are playing with several exciting new ones)? Again, no problem. NZCOM can load them in a jiffy. This makes for a whole new world of flexibility and adaptability, experimentation and education.

Need more memory to run a big application program? Fine. Just load a small operating system while that application is running. When it is finished, go back to the big system with bells and whistles like named directories, lots of resident commands, or special input/output facilities (such as keyboard redefiners or redirection of screen or printer output to disk).

Until you try this system, it is hard to imagine how easy it is to do these things. Gone are the days of taking source code (no source code is needed), editing configuration files (you don't need an editor), assembling (you don't need an assembler), and patching (you don't have to know how to use the arcane SYSGEN and DDT). Simple REL files for a particular module can be used by anyone on any system. Of course, if you want to create custom modules of your own special design, you can still do it, but this is no longer required, as it used to be. Hackers can hack, but users can simply use!

Joe and I are really hoping that NZCOM will open the world of Z System to the general community, to those who have no interest in learning to assemble their own operating system or do not have the tools or skills. If you have been at all intrigued by the Z System (how could you not have been?), now is your chance to experiment.

Getting NZCOM running is basically a two-step process, with each step remarkably easy to perform. First you define the system or systems you want. This is done with the program MKNZC (MaKe NZ-Com). Then you load the Z System you want using the program NZCOM. The details are explained below. Some comments of interest to the technically inclined are enclosed in brackets. Feel free to skip over them.

Defining NZCOM Systems

Here is how a person with a stock CP/M computer would go about getting NZCOM going. [First technical aside: Ironically, those of us who, with great skill and hard work, created manually installed Z Systems have a much harder job ahead of us. To use NZCOM effectively, we must first strip out all the ZCPR3 code in our fancy BIOSs and get back to a lean, Z-less system. I just spent the good part of an evening doing that for my BigBoard I computer (though, to be fair to my programming expertise, I should add that the hardest part was finding where I had stashed the BIOS source code).] For the discussion that follows, we will assume that the files in the NZCOM package have been copied onto a working disk in drive A.

As we said earlier, the first step is to use MKNZC, an easy menu-driven program, to specify the characteristics of our Z Systems. Its output is a descriptor file that is used later to load the system. What if you don't know enough yet about the Z System to make those choices? Again, no problem. There is a standard (or, in computer language, 'default') system defined for you already, and we will start by making it. We do that by entering the command line

A>mknzc nzcom

This will bring up a menu screen like the one shown in Fig. 1. The only difference on your system will be in the actual addresses for the modules, since they vary from computer to computer. Press the 'S' key to save the configuration. MKNZC displays a message to the effect that it is writing out the file NZCOM.NZC.

[Technical aside: Files of type NZC are NZCOM descriptor files. They are simple text files, as shown in Fig. 2. For those of you who write your own assembly language programs, you may notice a strong similarity to the symbol or SYM file produced by an assembler or linker (yep, identical). The symbols in this file define all the necessary parameters of the system to be created.]

From the values in Fig. 1, you can see that the default Z System offers every feature available. When this system is running later, the TPA (transient program area, the memory available for the application programs that do your real work) will be 49.0k bytes. This value, of course, is for my computer; as they say, "yours may vary." A 'k' or kilobyte is actually 1024 bytes, so this is really 50,176 bytes or characters. The original CP/M system, by the way, had a TPA of 54.25k bytes, so we are paying a cost of 5.25k bytes for this spare-no-expense Z System. As luxurious and opulent as this system is, it still leaves plenty of TPA for most application programs.

Sometimes, however, we have an application program that is really hungry for memory. Database managers, spread sheets, and C compilers often fall into this category. So does the new WordStar Release 4. We will now use MKNZC to define a minimum Z System for when we run those applications. To give this version the name MINIMUM, enter the command

A>mknzc minimum

When the menu comes up, press key '4'. You will be asked to define the number of records (128-byte blocks) to allocate to the input/output package or IOP. Enter '0' and press return. Similarly reduce to zero the allocations for the resident command package (RCP), flow command package (FCP), and named directories register (NDR). You will be left with the screen shown in Fig. 3. Press the 'S' key to save the definition of this minimal Z System in the descriptor file MINIMUM.NZC [shown in Fig. 4 for the technically inclined].

Notice that the TPA has grown to 53.25k, only 1k less than the original miserable CP/M system. Even with this meagre Z System, costing only 1k of TPA, you get the following features (and more):

  • multiple commands on a line

  • the alias facility that provides automatic command sequence generation

  • automatic, user-defined search path for COM files

  • extended command processing (ARUNZ, described in TCJ #31, for example)

  • error handling that tells you what's wrong with a bad command and allows you to correct it

  • shells (menu systems, command history shell for saving and recalling old commands, file-maintenance shells, etc.)

  • terminal-independent full-screen operation via Unix-like TCAP (terminal capabilities descriptor)

These are only two of a wide variety of possible Z Systems. As you gain experience with NZCOM, you can fine tune the definitions to meet all of your needs. For my BigBoard I computer, I have defined four systems. Two of them, called FULL and TINY, have the features shown in the two examples here. A third one is called SMALL. Not quite as diminutive as TINY, it sacrifices an additional 0.5k of TPA to retain the flow command package (FCP), which is so valuable in providing high levels of command automation. Even my voracious application programs can usually get by under this system.

Finally, I have a system called NORMAL, which, as the name implies, is the one I use most of the time. It is the same as FULL but without an IOP. The most common use for an IOP is to run keyboard redefiners like NuKey. Most people like this feature, but splendid as NuKey is, for some reason my style does not find much use for keyboard macros (I've become a rather skillful typist and can generally type faster than I can think of moving my finger to a special key), so I generally omit the IOP and gain 1.5k of TPA.

Loading the NZCOM Systems

Having defined the systems above, we can now fire them up even more easily. For the default NZCOM system, just enter the following simple command:


With no argument after the command name, NZCOM will load the system defined with the name NZCOM. As it does this, you will see a signon message on the screen, followed by a series of dots, each one indicating that another module has been loaded. [Technical aside: If you want to see more precisely what is going on, just add the option "/v" to the command to select verbose mode. You will then get a screen display something like that shown in Fig. 5. I'll have more to say about what all this means a little later.]

After NZCOM starts running, it executes a program called START.COM. This is usually an alias command, a program that simply passes another more complex command line on to the command processor. I will not explain the details of START here, but after it finishes, Z System will be up and running, waiting for your commands.

How NZCOM Works

This section is for the technically inclined, so if that's not you, pretend there are square brackets around this whole section and skip ahead to the next section. Here we are going to explain what some of those verbose-mode messages mean and what NZCOM is doing to create the system on the fly.

First NZCOM loads the descriptor file into memory. Among other things, this file has the information about which system modules to load and to what starting addresses. The first module loaded is the command processor. It is loaded from the file NZCPR.REL, which has the code for the command processor (ZCPR34) in so-called relocatable form.

There is some very interesting assembly/linkage razzle-dazzle that goes on here. With the REL files one usually plays with, only the run-time execution address of the code is unknown at assembly time and must be resolved by the linker. Things are much trickier here. When the command processor code was assembled, not only was its own run-time starting address unknown, but the addresses of various other system components, such as the message buffer and multiple command line, to which it refers in countless places, are also unknown. Since there is no fixed relationship between the addresses of the CCP and these other modules, there is no way to define the addresses using equates in the code.

Put another way, when NZCOM converts NZCPR.REL into actual object code, it must resolve not only the calls and jumps and data loads that refer to other locations in the command processor but also those that refer to the other system modules. Fortunately, advanced assemblers and linkers - including those from SLR Systems and a ZAS follow-on under development by Echelon - already have a mechanism to handle this problem. It was Bridger Mitchell who recognized how this mechanism, called named common, could accomplish what was needed here.

When code with symbols in named common is assembled, the corresponding bytes in the resulting REL file are marked not only for relocation but for relocation with respect to a specific common block. The SLR assemblers support up to 12 named common blocks. NZCOM contains very sophisticated linking code that resolves the references to data items in the common blocks, the addresses of which it gets, naturally, from the NZC descriptor file.

Fig. 6 shows a partial listing of the file NZCMN.LIB, which is referenced in a MACLIB statement in each module assembled for use by NZCOM. Seven named common blocks are defined: _BIOS_, _ENV_, _SSTK_, _MSG_, _FCB_, _MCL_, and _XSTK_ for the CBIOS, environment descriptor, shell stack, message buffer, external file control block, multiple command line buffer, and external stack, respectively. Note that no common blocks are defined for the RCP, FCP, or NDR. References to these package must be made indirectly at run time, using data obtained from the environment descriptor in memory.

How does the NZCOM loader figure out that the file NZCPR.REL is the command processor? You might think that it uses the name of the file, but, in fact even if you had a copy of it called MYNEWCP.REL, NZCOM would be able to load it just as well. The answer is that the source code contains the directive


which gives the REL file an internal module name. It is this name that NZCOM uses to determine what kind of module the code represents.

After the command processor is loaded, the other modules are loaded in succession in similar fashion, except for two. The named directory file NZCOM.NDR is a file that you can make or change with the standard utility programs MKDIR or EDITNDR/SAVENDR. There is nothing in an NDR file that requires relocation at all. The same is true for the Z3T terminal descriptor (TCAP) file. It can be created using the TCSELECT utility.

When all the loading is done, a copy of the command processor object code is written out to a file called NZCOM.CCP. This file is used for subsequent warm boots, since we obviously cannot warm boot from what is on the system tracks of the disk (the Digital Research command processor is still there, after all). At this point we can resume the non-technical discussion.

Changing NZCOM Systems

Now that you have Z System running, you can start to work with it and learn about it. I am not going to discuss Z System in general here; the subject is much too extensive. One thing you can do is to get out your back issues of TCJ and experiment with the programs described there. Another is to buy the "Z System User Guide" published by Echelon. That book describes the Z System from a less technical point of view than Richard Conn's "ZCPR3, The Manual", also published by Echelon.

What I would like to discuss now is some of the ways you can use the dynamic capabilities of NZCOM. First we will describe how you change the entire operating system. For these examples we will assume that you have been doing work in various directory areas on your system and that you have set up named directories. Let's say you are in your dBase II area now. Since you know that dBase II needs a lot of memory to run efficiently (or should I say 'tolerably', since it never runs efficiently!) and since (unlike WordStar 4, for example) it cannot make use of any Z System features anyway, you want to load the minimum system we created earlier. You can probably guess what the command is:

B2:DBASE>nzcom minimum

[More technical stuff: Fig. 7 shows the screen display you would get with the "/v" verbose option on this command.] For the minimum system NZCOM loads only a command processor, disk operating system, and virtual BIOS. The other system segments disappear. This includes the NDR or named directory register, so the prompt changes to


The START alias does not run this time. It runs only when NZCOM is loaded from a non-NZCOM system (such as CP/M).

In general, when loading a new version of the operating system from another that is currently running, NZCOM loads only the modules that must be loaded, either (1) because they did not exist before or (2) because they are now at a different address or have a different size. For example, when I load my FULL system from the NORMAL system to add an IOP, only the CCP, DOS, BIOS, and IOP are loaded, since the RCP, FCP, and NDR are in the same place as before and have the same size. When modules do have to be loaded, files with the default names shown in Fig. 5 are used. Later we will discuss how you can load modules with other names.

There are a number of system modules that never change in the present version of NZCOM. (Yes, like the famous Al Jolson lines, you ain't seen nothin' yet!) These include the environment descriptor, message buffer, shell stack, path, wheel byte, and multiple command line buffer. With the exception of module addresses in the environment descriptor, data in these fixed system modules remain unaffected. This means that if you had selected an error handler, for example, or a shell such as a command history shell, they will still be in effect after a change of system.

Because the multiple command line buffer is preserved through the load of a new system, you can include NZCOM commands as part of multiple command sequences, alias scripts, and shell (MENU, VMENU, or ZFILER) macros. Thus, for example, you could have entered the command

B2:DBASE>nzcom minimum;dbase etc.

In this case the operating system would have changed, and then DBASE would have started running. I will not go into the technical details here, but there are ways to write an alias script, which might be called DB, that would check to see if the minimum system was already running and, if not, automatically load it before invoking DBASE.

Nothing says the operating system can change only once in the course of a multiple command line. You might have alias scripts that change to a minimum system, run a specific command, and then reload the normal system again. There is a time penalty associated with this (though very little if you have the NZCOM files on a RAM disk), but the result is that the application program sees a big TPA while it is running, but you always see a nice, full-featured Z System.

NZCOM does not even insist that you stay in Z System. On the contrary. On a cold load from CP/M it will build (if it does not exist already) a program called NZCPM that, when run from Z System, will restore the original CP/M system.

[Technical aside: Even if you need absolutely every available byte of TPA, you can still automate the process. You can use the submit facility to run a batch job that exits from Z System entirely, runs an application under plain CP/M, and then returns to Z System. You do have to observe some precautions. For example, you have to make sure that all command lines in the batch file that will execute while Z System is not in effect are valid CP/M commands. Once the batch script has reloaded Z System using the NZCOM command, it can resume using appropriate Z System commands, including multiple commands on a line.

Another factor to bear in mind is that NZCPM returns you to CP/M in drive A user 0 no matter where you were when it executed. Since ZCPR3 (starting with version 3.3) writes its submit file to directory A0 rather than the current directory, there is no problem with continuing operation of the batch file under CP/M. However, when you reload NZCOM (it will be a cold load, including execution of START), you will not automatically be back in your original directory. End aside.]

Changing Parts of the System

The NZCOM command is not limited to loading whole new operating systems; with a slightly different syntax it can also load individual system modules, rather like the LDR program in a manually installed Z System. There are two important differences, however.

The first is that NZCOM loads code modules (IOP, RCP, and FCP) from REL files rather than from absolute files such as SYS.FCP or DEBUG.RCP. Absolute files can still be loaded using LDR, but this is undesirable under NZCOM, since the addresses of the modules may change as different systems are loaded. NZCOM has the advantage of using a single REL file no matter which system it is being loaded into. In the future, RCPs, FCPs, and IOPs will be distributed in REL form instead of (or in addition to) source code form. The REL file is much smaller and can be used without knowing how to assemble the code.

The second difference is that NZCOM can load command processors and disk operating systems as well. This makes it very easy to change versions of the command processor (with or without security or named directory or submit support, for example) or to experiment with alternative DOSs, such as Z80DOS or P2DOS. This will be a real boon to the development of new operating system components, since one can test new versions so easily and quickly.

For convenience, NZCOM can also load named directory files (of type NDR) and terminal descriptor files (of type Z3T). This is so that you do not have to have LDR.COM on your disk. On an NZCOM system, LDR is a dangerous command, since it does not have safeguards against loading absolute system components to addresses for which they were not assembled. With an NZCOM system, you should remove LDR.COM from your disk.

Other NZCOM Features

There are many more things that could be said about NZCOM that I will save for another time. There is just one more that I want to mention now, and that is the extra "Custom Patch Area" that can be defined with MKNZC (see Fig. 1). This option in MKNZC allows one to establish an area in protected memory just below the CBIOS (custom BIOS or real BIOS). This area can be used by various operating system extensions that one wants to preserve from one NZCOM system to another.

Because of the techniques it uses for patching the Z System onto CP/M, NZCOM will not work when a resident system extension (RSX) is present. Thus, for example, you cannot run NZCOM from inside a ZEX script or if DateStamper or BYE is active in low memory (if they are loaded above the CBIOS, there is no problem). I am presently using the patch area for DateStamper. With NZCOM you can effectively have an above-BIOS version of DateStamper without having to move your BIOS down.

I am also planning to experiment with putting BYE in the custom patch area. I think this can be made to work, and it would permit NZCOM to be used on my Z-Node (and I mean used actively - so that the NZCOM system can be changed even from a remote terminal!).

There are special facilities in NZCOM that I do not have the energy to explain now whereby information about a currently running system can be extracted before the new system has been loaded and used to initialize the new system just before NZCOM turns over control to it. This allows an RSX's hooks into the operating system to be maintained.

ZCPR Version 3.4

Now let's turn to the subject of ZCPR version 3.4, which will be released along with NZCOM. Z34, as I will refer to it, is much more an evolutionary step from Z33 than Z33 was from Z30. There are four new features worth pointing out.

Type-4 Programs

The most important and exciting enhancement is the introduction of what is called the type-4 program.

With Z33 I added support for a new kind of program to run under ZCPR3. Programs designed to take advantage of the special features of the Z System have at the beginning of the code a special block of data called the Z3ENV header. This header identifies the program as a ZCPR3 program and contains the address of the ZCPR3 environment descriptor, where all the information necessary to find out about the Z System facilities is available. It also contains a type byte. Conventional Z System programs were of type 1. (Type-2 programs are similar but actually have the entire environment desciptor in the header. Programs of this type are extremely rare. In some senses they are a holdover from ZCPR2 and now obsolete.)

For the new type-3 program I added an additional datum in the Z3ENV header: the starting address for which the code had been assembled or linked. The command processor automatically loads the file to that address before transferring control to it.

Type-3 programs are usually linked to run in high memory (for example, 8000H or 32K decimal) where they do not interfere with most data or code in the TPA. Programs that run as extensions of the operating system (viz. history shells, extended command processors, transient IF processor) or as the equivalents of resident programs (viz. ERA.COM, REN.COM, SAVE.COM) are particularly suitable for implementation as type-3 programs. One cannot always foresee when these programs will be invoked, and it is nice if the contents of memory at the bottom of the TPA are not affected when they do run.

With type-3 programs one must choose in advance the address at which they will run. If the address is too high, there may not be enough room for them to load, and if too low, they are more likely to interfere with valuable TPA contents. In most situations it would clearly be preferable if the program could be loaded automatically as high as possible in memory. I thought of this from the beginning but compromised on the type-3 construct because it was so easy to code.

Joe Wright was not satisfied with this compromise. He soon wrote an initial version of the type-4 program, which does relocate automatically to the top of memory. With a lot of cooperation between us, we have honed it to the point where it functions very nicely and does not add very much code to the command processor.

Because type-3 programs run at a fixed address, albeit not necessarily 100H, they can be assembled and linked in the usual fashion, and the program files contain actual binary object code. Type-4 programs, on the other hand, must be relocatable by the command processor at run time. Thus object code alone is not sufficient.

One possibility would be to use a REL file directly. This would have been very convenient, but the code required to load a REL file is far too complex to include in a command processor running in a 64K memory segment. There is a less familiar relocatable type file known as a PRL (Page ReLocatable) file that, because it restricts the relocation to page boundaries (and other reasons), is much easier to relocate.

A PRL file consists of three parts. The middle part is a standard code image for execution at 100H. After this comes what is called a bit map, where, for each byte in the code image, there is a bit of 0 or 1 to tell whether that byte must be offset for execution at a different page. The bit map is one eighth the length of the code image. Finally, one page (256 bytes) at the beginning of the file serves as a header. This header contains information about the size of the program so that the code that loads it can figure out where the object code ends and the bit map begins.

In the type-4 program, this header is extended to include the code necessary (1) to calculate the highest address in memory at which the program can be loaded and (2) to perform the code relocation to that address using the bit map. The way this is accomplished is somewhat intricate.

The command processor loads the first record of the type-4 file into the temporary buffer at 80H as usual to determine the program type. If it is type 4, the CCP then calls the code in the header. That code calculates the load address and then (this clever idea was Joe's) calls the command processor back to load the program code and bit map into memory at the proper address. When this call is complete and control returns to the header code, it then performs the relocation of the code image at the execution address in memory. Only then is control returned to the command processor for initialization and execution of the program.

The result of this tricky scheme is that most of the type-4 support code that would otherwise have been required in the command processor is in the header instead (this was my contribution to the type-4 concept). Since a PRL file has a two record header anyway (almost all of which is otherwise empty), you get to add this code for free.

Joe pointed out to me some dangers with my type-3 construct. Suppose a type-3 program designed to run at 8000H is somehow loaded to 100H instead. Any attempt to execute it is likely to have less than desirable consequences, to put it mildly. This was not a serious problem with a normal (at the time) ZCPR33 system. Since the command processor would automatically load the type-3 program to the correct address, it took some deliberate action by the user to create the dangerous situation described. Of course, the poor fellow still running ZCPR30 who decided to try out a type-3 program...

However, now that NZCOM is here, the user may very well decide to drop back into CP/M from Z System to perform some tasks. In this situation, a type-3 program is a live weapon, just waiting to blow up the system. The type-4 program poses a similar danger.

We have come up with two defense strategies. One can be implemented in the program itself. There is code (TYP3HDR1.Z80) that can be placed at the beginning of a type-3 program (based on ideas conceived independently by Bob Freed and Joe Wright) that will verify that the code is running at the proper address. This part of the code is, as it must be, address independent (it uses only relative jumps). If the load address is found to be wrong, a warning message is displayed and control is returned to the command processor before any damage can be done. This is the friendlier method, but it makes the programs longer.

The second defense method does not impose any overhead on the program code. It is easier to use than the other method, and it can generally be patched into existing type-3 programs in object form. It can also be applied with type-4 programs, for which the first method cannot be used (type-4 files begin with a relocation header and not with program code, and the system must be prevented from trying to execute the header when the program is invoked under CP/M).

With this method, one places a byte of C7H, the RST 0 instruction opcode, at the beginning of the file. Execution of this instruction causes a call to address 0, which induces a warm boot. This behavior may be puzzling to the user, but at least it does no damage. How, then, will such a program ever execute? The answer is that ZCPR34 checks the first byte of a type-3 program to see if it is a C7H. If it is, the command processor replaces it with a C3H, the JP instruction opcode. To take advantage of this method, the program code must begin with a "JP START" instruction in which the JP is replaced by RST 0 (note: you cannot use JR START instead). The proper assembly language source code is illustrated in Fig. 8. Note that the replacement of the RST 0 by a JP is not required with a type-4 program since the header (which is where this construct appears) is never intended to be executed as a standard program, even under Z34.

The Extended Environment Descriptor and the Drive Vector

The definition of the ZCPR3 environment descriptor has been modified and extended. I will not go into all the details here, but I will describe the main changes.

First, to make some space available for additional important information, the extended ENV eliminates definitions for all but one console and one printer. Eventually there will be a tool (utility program) that allows interactive or command-line redefinition of the characteristics of these single devices so that you will actually have more rather than less flexibility.

The extended ENV will now contain the addresses and sizes in records of the CCP, DOS, and BIOS (actually, the size of the BIOS is not included). This information has been added to deal with problems in some special operating system versions where the CCP and/or DOS do not have their standard sizes of 16 and 28 records respectively, such as in the Echelon Hyperspace DOS for the DT-42 computer. Future versions of NZCOM, which will support variable CCP, DOS, and BIOS modules, will also need this.

Finally, a long needed feature has at last been implemented; a drive vector. The maximum-drive value in the ENV was not adequate in a system with non-contiguous drives (A, B, and F, for example). Now you can tell the system exactly which drives you have on the system, and the command processor will do its best to prevent references to nonexistent drives.

Ever More Sensible Named Directory Security

With Z33 I made it possible to refer by drive/user (DU) to directories beyond the range specified by the maximum drive and maximum user values in the environment provided the directory area had a name with no password. It seemed only reasonable that if a user could access the drive by name, he should be allowed to access it by its equivalent DU as well.

The converse situation, however, was not handled according to similar logic. Suppose the maximum user was 7 but there was a password-protected named directory for user 6. Under Z33 one had the anomalous situation that the user could refer freely to the directory using the DU form but would be pestered for the password if he used the named-directory (DIR) form. This just didn't seem reasonable, and Z34 has corrected this.

Extended ECP Interface

With Z34 I have added an additional option along the lines of BADDUECP. The BADDUECP option allows directory-change commands of the form NAME: or DU: that refer to illegal directories to be passed on to the extended command processor (ECP) instead of directly to the error handler. On my Z-Node, for example, I use the ARUNZ extended command processor to permit references to reasonable facsimiles to the actual directory names to work via alias scripts.

With Z33 attempts to execute a command containing an illegal wildcard character or with an explicit file type would be flagged as errors and passed directly to the error handler. With Z34 one has the option (via the option BADCMDECP) to pass these forms of bad command to the extended command processor as well.

Here are a couple of examples of how this feature can be used with the ARUNZ extended command processor. First, one can enter the following script into the alias definition file ALIAS.CMD:

?  help $*

Now when a user enters the command "?", he will get the help system instead of an error message telling him that he entered a bad command.

You can also use this facility to allow further shorthand commands. With the script definition

DIM.Z3T   ldr dim.z3t
(or nzcom dim.z3t)

Now you can load the dim-video TCAP for your system simply by just entering the name of the TCAP file. Using wildcard specifiers in the name of the alias script, you can make any command with a type of Z3T load the corresponding TCAP file. Similarly, entering the name of a library (for example, LBRNAME.LBR) on the command line could automatically invoke VLU on that library. The same concept would allow one to enter the name of a source-code file (for example, THISPROG.Z80 or THATPROG.MAC) to automatically invoke the appropriate assembler (Z80ASM/ZAS or SLRMAC/M80 for these two examples).

This feature opens another whole dimension for experimentation, and I am sure that users will come up with all kinds of new ways to use it. PLEASE NOTE: if this feature is implemented, you cannot use the old version of ARUNZ that I so painstakingly documented in my last column (alas, barely born and already obsolete). Previous versions of ARUNZ used '?' and '.' for special purposes. Those characters were carefully chosen because they could never appear in command names passed to ARUNZ, but now they can! Therefore, in version 0.9H of ARUNZ I have changed these characters to '_' (underscore) instead of '?' and ',' (comma) instead of '.'.

That's it for this issue, I'm afraid. I still didn't get to a discussion of defects in the shell coding for WordStar 4 (I hope these will be corrected in version 5, which is apparently really in the works at this time). My discussion of the ZEX in-memory batch processor and the improvements I have been making to it will also have to wait still longer.

1.* Command Processor CCP BD00 16 Records
2.* Disk Operating System DOS C500 28 Records
3.* NZ-COM Bios BIO D300 2 Records

4. In/Output Processor IOP D400 12 Records
5. Resident Command Proc RCP DA00 16 Records
6. Flow Control Processor FCP E200 4 Records
7. Named Directory Reg NDR E400 14 Names

8.* Environment Descriptor ENV E500 2 Records
9.* Shell Stack SHS E600 4 Entries

P. Custom Patch Area PAT 0000 0 Records
Customer's CBIOS TOP E800

Effective TPA size 49.0k

* Items 1, 2, 3, 8 and 9 are not changeable in this version.

Selection: (or <S>ave or <Q>uit) _

Figure 1.
Screen displayed by the MKNZC program when run under CP/M. This is the standard or default system definition.


0010 RCPS D400 IOP 000C IOPS E200 FCP 0004 FCPS
E400 Z3NDIR 000E Z3NDIRS E700 Z3CL 00CB Z3CLS E500 Z3ENV
0002 Z3ENVS E600 SHSTK 0004 SHSTKS 0020 SHSIZE E680 Z3MSG
0010 MAXDRV 001F MAXUSR 0001 DUOK 0000 CRT 0000 PRT
0050 COLS 0018 ROWS 0016 LINS FFFF DRVEC 0000 SPAR1
0050 PCOL 0042 PROW 003A PLIN 0001 FORM 0066 SPAR2
0042 SPAR3 003A SPAR4 0001 SPAR5 BD00 CCP 0010 CCPS
C500 DOS 001C DOSS D300 BIO 0000 PUBDRV 0000 PUBUSR

Figure 2.
For the technically inclined, this is a listing of the contents of the NZCOM.NZC system descriptor file produced by MKNZC.


1.* Command Processor CCP CE00 16 Records
2.* Disk Operating System DOS D600 28 Records
3.* NZ-COM Bios BIO E400 2 Records

4. In/Output Processor IOP 0000 0 Records
5. Resident Command Proc RCP 0000 0 Records
6. Flow Control Processor FCP 0000 0 Records
7. Named Directory Reg NDR 0000 0 Names

8.* Environment Descriptor ENV E500 2 Records
9.* Shell Stack SHS E600 4 Entries

P. Custom Patch Area PAT 0000 0 Records
Customer's CBIOS TOP E800

Effective TPA size 53.25k

* Items 1, 2, 3, 8 and 9 are not changeable in this version.

Selection: (or <S>ave or <Q>uit) _

Figure 3.
Screen displayed by the MKNZC program after eliminating the IOP, RCP, FCP, and NDR modules in order to define a minimal Z System.


0000 RCPS 0000 IOP 0000 IOPS 0000 FCP 0000 FCPS
0000 Z3NDIR 0000 Z3NDIRS E700 Z3CL 00CB Z3CLS E500 Z3ENV
0002 Z3ENVS E600 SHSTK 0004 SHSTKS 0020 SHSIZE E680 Z3MSG
0010 MAXDRV 001F MAXUSR 0001 DUOK 0000 CRT 0000 PRT
0050 COLS 0018 ROWS 0016 LINS FFFF DRVEC 0000 SPAR1
0050 PCOL 0042 PROW 003A PLIN 0001 FORM 0066 SPAR2
0042 SPAR3 003A SPAR4 0001 SPAR5 CE00 CCP 0010 CCPS
D600 DOS 001C DOSS E400 BIO 0000 PUBDRV 0000 PUBUSR

Figure 4.
For the technically inclined, this is a listing of the file MINIMUM.NZC, which describes a minimum-size version of an NZCOM system for the computer in Figs. 1 and 2.


A>nzcom /v
NZCOM Ver 2.0 Copyright (C) 1987-88 Alpha Systems Corp. 21 Jan 88
Input buffer start 1C00
Read buffer start 1D00
Write buffer start 3D00
Loading A0:NZCOM.NZC
Loading A0:NZCPR.REL for BD00 at 3D00
Loading A0:NZDOS.REL for C500 at 4500
Loading A0:NZBIO.REL for D300 at 5300
Loading A0:NZIOP.REL for D400 at 5400
Loading A0:NZRCP.REL for DA00 at 5A00
Loading A0:NZFCP.REL for E200 at 6200
Loading A0:NZCOM.NDR for E400 at 6400
Loading A0:NZCOM.Z3T for E580 at 6580
Writing A15:NZCOM.CCP
Booting NZ-COM...

Figure 5.
This is the screen display produced by NZCOM as it loads the default system definition NZCOM.NZC with the verbose option.


; Named COMMON declarations start here
; For compatibility, these are the same names used by Bridger Mitchell's
; JetLDR

common /_BIOS_/
cbios: ; Customer's bios address

common /_ENV_/
z3env: ; Z3 Environment descriptor
z3envs equ 2 ; Size (records)
rcp equ z3env+12
rcps equ yes ; Used as existence test, not size
fcp equ z3env+18
fcps equ yes ; Used as existence test, not size
z3ndir equ z3env+21
z3ndirs equ yes ; Used as existence test, not size

drvec equ z3env+52 ; Valid drive vector

ccp equ z3env+63 ; CCP entry
ccps equ z3env+65 ; Size

dos equ z3env+66 ; DOS entry (+6)
doss equ z3env+68 ; Size

bio equ z3env+69 ; BIO entry

common /_SSTK_/
shstk: ; Top of Shell stack
shstks equ 4 ; 4 entries
shsize equ 32 ; 32 bytes each

common /_MSG_/
z3msg: ; Message buffer
z3msgs equ 80 ; 80 bytes long

common /_FCB_/
extfcb: ; External file control block
extfcbs equ 36 ; 36 bytes long
expath equ extfcb+extfcbs ; External path
expaths equ 5 ; 5 elements
z3whl equ expath+(expaths*2)+1 ; The wheel byte
z3whls equ 1 ; 1 byte

common /_MCL_/
z3cl: ; Multiple command line
z3cls equ 203 ; Maximum command length
nzpat equ z3cl+256 ; Potential User patch area

common /_XSTK_/
extstk: ; External stack
extstks equ 48 ; Size (bytes)

cseg ; Select Code Segment

; End of NZCMN.LIB

Figure 6.
This is a partial listing of the file NZCMN.LIB, which defines the named common blocks used during assembly of modules for use by NZCOM.


B2:DBASE>nzcom minimum /v
NZCOM Ver 2.0 Copyright (C) 1987-88 Alpha Systems Corp. 21 Jan 88
Input buffer start 1C00
Read buffer start 1D00
Write buffer start 3D00
Loading A0:NZCPR.REL for CE00 at 3D00
Loading A0:NZDOS.REL for D600 at 4500
Loading A0:NZBIO.REL for E400 at 5300
Loading A0:NZCOM.Z3T for E580 at 5480
Writing A15:NZCOM.CCP
Booting NZ-COM...

Figure 7.
This is the screen display when NZCOM loads the minimum system from a running default system.


ENTRY: ; Beginning of program
DB 0C7H ; RST 0 opcode, will become JP
DB 'Z3ENV' ; ZCPR3 program ID
DB 3 ; Type 3
ENVADR: DW 0 ; ENV address filled in by Z34
DW ENTRY ; Execution address
START: ; Beginning of main program

Figure 8.
Form of the Z3ENV header code in a protected type-3 program. An attempt to execute this code under CP/M will result in a warm boot.

[This article was originally published in issue 32 of The Computer Journal, P.O. Box 12, South Plainfield, NJ 07080-0012 and is reproduced with the permission of the author and the publisher. Further reproduction for non-commercial purposes is authorized. This copyright notice must be retained. (c) Copyright 1988, 1991 Socrates Press and respective authors]