CP/M

home *** CD-ROM | disk | FTP | other *** search

/ CP/M / CPM_CDROM.iso / jsage / znode3 / tcj / tcj51.ws < prev next >

Wrap

Text File | 1994-09-02 | 25.3 KB | 562 lines

R60 Z-System Corner The Trenton Computer Festival Jay Sage Announcements The announcements for this time are about some excitingì price reductions. A small band of programmers has longì enjoyed the help of the wonderful DSD (Dynamic Screenì Debugger) in getting the bugs out of our code. The $130ì price tag, however, was a deterrent to many. I recentlyì located and spoke with the author, John Otken, and suggestedì that there would be a great advantage in reducing the price.ì More people would get to take advantage of his superbì program, and he would actually make more money because ofì the increased sales. He agreed to my suggested price of $50! I hope that many more of you will take advantage of thisì opportunity. DSD is not only a powerful aid in debuggingì problems with code; it is also a wonderful way to learnì about how programs work. The full-screen display allows oneì to see everything that is happening during programì execution. One sees a section of disassembled source code,ì the contents of the CPU registers, the contents of theì stack, and two blocks of memory. In all cases, symbolic asì well as numeric data can be seen, and all user entries canì make use of defined symbols. There have been two price reductions of interest toì owners of SB180 computers. XBIOS has been reduced from $75ì to $50, as a reflection of the fact that it is no longerì actively supported. We have also acquired the remainingì stock of the excellent Electronic Technical Servicesì ETSIO180+ board. Its low power CMOS design includes aì battery-backed real-time clock, two high speed (115.2 kbps)ì serial ports, 24 bits of parallel I/O, and an SCSI interfaceì for hard disk drives. It is fully supported by XBIOS (whichì is required to run the board). I use the ETSIO180+ on my ownì computer and have been very satisfied with it. The originalì price was $280; we will sell the remaining stock (currentlyì about six boards) for just $100 each (or $145 includingì XBIOS). The Trenton Fiascos The main contents of my column for this month wereì originally intended for publication in the printedì proceedings for this year's Trenton Computer Festival.ì Although _our_ session there was again a great successì (because of the speakers), the organization of TCF hasì deteriorated alarmingly over the past few years. When I originally sent in my speaker form for TCF, Iì checked the box indicating that I would contribute a writtenì piece. Shortly before the deadline, when they had notì received my submission, I was called by Sol Libes, who runsì the conference, asking if I was going to write something. Iì told him that I was still interested if there was time. Heì said that it could be accepted if I got it in by the end ofì the next weekend. We agreed that I would upload it to theì board run by the Amateur Computer Group of New Jersey. Onceì it was there, I was to call Sol. I worked extremely hard for a couple of days, staying upì until 3 am to get it finished and uploaded to the ACGNJì board. As instructed, I placed a voice call to Sol. He wasì not there, so I left a message on his answering machine.ì When he did not call back, I called several more times,ì leaving messages each time. Finally he returned my call, andì we agreed that he would call me again if there was anyì problem with the file I had left for him. I never heardì anything further. You can imagine my dismay when I learned during theì festival that my article had not been included. I still haveì no idea why, as no one has had the courtesy to contact me.ì Was its omission deliberate? I'm inclined to think it wasì administrative incompetence, since most other aspects of theì conference organization were also handled poorly. On my speaker registration form I had checked boxesì indicating the equipment that I wanted them to supply in ourì meeting room. My speaker confirmation form indicated thatì the information had been recorded, but I telephoned theì program coordinator the day before I drove down just to beì absolutely sure. Do you think the equipment was there? No.ì And do you think that anyone at TCF knew what to do aboutì it? No. We had to struggle through a couple of talks before,ì almost by accident, we stumbled upon the people who had theì equipment (no one had told them we needed it). I had hoped that the following material would be read byì an audience that might include many people with CP/Mì computers who did not know that magazines like TCJ andì advances like Z-System existed. So that my effort on thisì composition was not totally wasted, I am presenting it here. CP/M Is Not Dead! I'm sure you all know the famous Mark Twain anecdote.ì Somehow the newspapers picked up a story that he had died. ì At his next public appearance he delighted in relating thatì his reported death was, as he put it, "greatly exaggerated." ì The rumored death of CP/M, the granddaddy of microcomputerì operating systems, is similarly exaggerated! Unfortunately, the erroneous impression about CP/M isì much harder to correct. Were it simply the result of falseì reports in the media, one could bring the truth to theì media's attention and have them publish a correction.ì Regrettably, the belief that CP/M is dead arises via a ì mechanism that cannot be used to correct the view. I will try here to give you some impression of theì vitality that continues to flourish in the CP/M world,ì particularly in connection with the development of the Z¡ System, a highly advanced successor operating system toì CP/M. While maintaining total compatibility with CP/M andì its software base, the Z-System brings concepts and featuresì that are as advanced as can be found on any computerì anywhere. Nothing can give a 4-MHz Z80 with 64 kilobytes ofì memory the raw computing horsepower of a 33-MHz 80386ì microprocessor with several megabytes of memory, but the Z-ì System can give an old CP/M computer a surprisingly powerfulì user interface and can turn it into a fun, educational, andì productive machine. At the end of this article, I have listed three magazinesì with strong CP/M support. By subscribing to them you will beì able to learn about sources for public-domain programs andì the names and addresses of vendors who actively supportì 8-bit software and hardware products. You are also welcomeì to call me. Why Do People Think CP/M Is Dead? ================================= The community did not learn of the death of CP/M, as withì Mark Twain, by reading a report; they inferred it fromì personal experience. The mainline computer magazines, suchì as Byte, gradually carried less and less news about CP/Mì until eventually they carried none. Why did they stop? ì Basically because the volume of interest shifted naturallyì enough to MS-DOS and the newer hardware. There was no longerì much activity in CP/M hardware development or sales, andì almost all mainline software houses stopped developing newì CP/M programs. Soon most of them stopped even offering theirì old CP/M programs for sale. Some, like Borland, have evenì gone so far as to deny that CP/M products they once offeredì were _ever_ offered by their company! (I swear I remember aì Borland Turbo Modula 2, but many people tell me that whenì they contact Borland they are _assured_ that Borland _never_ì offered that product.) This situation notwithstanding, a very high level of CP/Mì activity did continue, but not in the spotlight. There wereì smaller, specialty magazines that continued to focus onì hobbyist computing, and there were also smaller softwareì vendors who continued to support CP/M with great ì enthusiasm. For veteran CP/M users there was some chance ofì their learning about these alternate sources of supportì before the mainline sources shut the door on CP/M, but evenì many of the veterans lost touch. For new owners of CP/M computers -- and though it mightì surprise you, there are many -- the situation is worse. ì Typically, they have inherited a retired CP/M computer fromì a family member, friend, user group, or even a stranger. ì When they try to contact the sources for CP/M informationì and support listed in their old documentation, they findì them to be either out of business totally or at least out ofì the CP/M business. And these days the sales representativesì at the software houses have often never even heard of CP/M! ì No wonder these new CP/M computer owners conclude that CP/Mì is dead. The Real Story ============== It is natural that the major focus of interest inì computers will continually shift toward the latest, mostì advanced, and most widely sold hardware. Nevertheless, aì tremendous level of activity still exists in the CP/M world,ì most of it centered on the further development of the Z-ì System. Why would someone still be interested in CP/M? Theì special spirit that persists in the CP/M world is oneì important factor. As in the Unix world, there is a veryì strong sense of community and sharing. This includes a wellì established tradition of public-domain software, that is,ì programs written specifically for the benefit of the generalì community and shared totally with that community. Byì contrast, the MS-DOS world has what they misleadingly callì "shareware." These programs are distributed for free, butì users are told that they must send money to the author ifì they continue to use them. A second attraction in the CP/M world is the intellectualì challenges and rewards it offers. The relative simplicity ofì the Z80 microprocessor and the CP/M operating system allowì easy entry to new programmers. Although extremely rare inì the DOS world, it is nearly universal in the CP/M world thatì programs are published with source code. This has severalì far-reaching consequences. In terms of quality, it meansì that the development of a program is not limited to theì conceptual and coding ability of a single author. Others inì the community can take that source code, make improvementsì to the program, and return the results to the community.ì Many of the most important CP/M programs have a very longì history of development involving many authors. Reading source code is also an indispensable vehicle forì learning about how a computer system works. New programmersì can quickly learn coding techniques and apply them to newì applications. Amazingly, source code is available not onlyì for the numerous utility programs but also for at least ì some versions of all parts of the operating system as well. The seminal event in the survival of CP/M took placeì almost exactly a decade ago. Richard Conn, eager to make hisì own contribution to a community that he felt had helped himì so much, spearheaded a group effort to write replacementì code for the Console Command Processor (CCP) portion of theì CP/M operating system. The result, named ZCPR for Z80ì Command Processor Replacement, was released to the public inì February, 1982. Not much later, I discovered this much improved commandì processor and installed it on my CP/M computer. Then I didì something even more significant: I looked at the sourceì code. To my amazement, I discovered that the operatingì system, that "holy of holies," is nothing more than a ì computer program, rather like any other, and that I, albeitì untrained in systems programming, could not only understandì it but experiment with changing it! Discoveries like thisì from reading source code continue to inspire new CP/Mì hobbyist programmers, and computer bulletin boards and userì group meetings continue to be scenes of intense discussion. The Features of Z-System ======================== The ZCPR command processor has gone through severalì stages of evolution, and the same approach has now beenì applied as well to the Basic Disk Operating System (BDOS)ì component of the CP/M operating system. The combined resultì is now referred to as the Z-System, and it represents a ì remarkable point in the development of microcomputerì operating systems. It has many, many features inspired byì minicomputer and mainframe operating systems and some notì available even on those powerful machines. When I use my DOSì 386 machine at work, there are many Z-System features that Iì sorely miss, and I am constantly amazed at their absenceì from an operating system whose code is bigger than theì entire memory address space on a CP/M machine! For the most part, the original Digital Research CP/Mì accomplished in admirable fashion the essential functions itì was required to perform: to run a few resident commands andì to load external commands from disk. However, it devotedì little attention to the user interface and did not provideì many services to make the operator's life easy. To be fair,ì of course, CP/M was born in the days when 16K of memory costì about $500 (in 1970s dollars, no less) and occupied anì entire S-100 card, roughly the size of the motherboard of aì modern DOS machine. The central goal of the Z-System since the beginning hasì been to make it easier and more convenient to operate theì computer. My own ideal has been to have the computer performì all tasks that it can handle on its own and to leave to theì user only those tasks that a computer cannot figure out byì itself. In other words, the computer should take care of allì the routine matters; the human operator should handle onlyì the thinking. I will now run through a short summary of Z¡ System features and try to indicate how they make theì operator's life easier. User Area Access CP/M introduced the concept of disk "user" areas, whichì allowed the operating system to group files into separateì logical directories. Unfortunately, CP/M provided noì practical way to access files across user areas, which madeì them almost useless. Z-System makes it very easy and convenient to organizeì your files. Where CP/M allowed only a drive prefix in fileì specifications (e.g., B:TEXT.DOC), Z-System allows driveì and/or user number prefixes (e.g., A3:WORK.WS) so that filesì in other user areas as well as other drives can beì referenced directly. In addition, Z-System allows meaningfulì names (similar to DOS subdirectory names) to be assigned toì drive/user areas (so we might have LETTERS:JOE.WS). Thisì provides an interface that is far more suitable to the wayì people think and remember. Terminal Independence and the Environment While some would argue that the DOS hardware and softwareì standards established by IBM's market dominance haveì resulted in an enforced mediocrity, there is no doubt thatì having a single environment in which to operate makes lifeì much easier for applications programmers. Programs for DOSì generally work right out of the box on any IBM-compatibleì computer. Configuration is required only for fine-tuning. CP/M, on the other hand, was designed to allow programsì to run on an extremely wide variety of hardware. In thoseì days, "personal" computer took on a different meaning --ì each person designed and built his own hardware. CP/M couldì be made to work with all of them, but elaborate ì configuration procedures were generally required, especiallyì to match programs to the particular terminal used. To thisì day, we still have to deal with this hardware diversity. What CP/M could have provided, but didn't, was a meansì for conveying to application programs information about theì operating environment. Z- System has several modules thatì afford such communication. An area called the environmentì descriptor (ENV) contains information about the system ì configuration. Another system area called the message bufferì (MSG) stores information that one program can leave for useì by another program that runs later. Part of the ENV is a section called the TCAP or Terminal¡ CAPability descriptor (if you know Unix, you will recognizeì this). When the appropriate TCAP has been loaded, a Z-Systemì program will automatically use the right video control codesì for that terminal. Command Processing Enhancements Under CP/M, you had to specify where the COM file to beì run was located (otherwise the current drive was assumed). ì This is a perfect example of something that a computer canì easily be smart enough to do for you, and Z-System does. Asì with modern versions of DOS (which took many years to catchì on to this Z-System feature), you specify a list ofì directory areas that the operating system will scan for aì requested COM file. Unlike DOS, Z-System does not insistì that the current directory be first in the path; it canì appear wherever you want it to, or not at all. With Z-System one is also no longer limited to issuingì commands one at a time (DOS has been even slower to catch onì to this). A single line of command input can contain a wholeì sequence of commands. As a result, you do not have toì interrupt your thinking to wait for one command to finish ì before you can specify the second and subsequent steps in aì process. You can work out a strategy for what you want toì accomplish and issue all the commands at once, before youì forget or get confused. Many oft-repeated computational tasks involve sequencesì of commands (e.g., editing, spell-checking, printing). Inì such cases, the Z-System alias facility (similar in someì ways to CP/M's submit or DOS's batch operations but far moreì flexible -- more akin to Unix scripts) can be used to defineì a new command name, which, when invoked, performs the entire ì sequence. This saves the user a lot of typing but moreì importantly eliminates the need to remember exactly what theì sequence is. Basically, you solve the problem once and putì the solution into an alias script. From then on, theì computer is smart enough to take care of the complex ì details for you. Conditional Command Execution There is only so much one can accomplish on a computerì (or in life) without making decisions. Have you ever seen aì programming language with no ability to perform tests andì act in different ways depending on the results? Flow controlì (IF/ELSE/ENDIF) is unique to the Z-System command ì processor. Other operating systems that offer flow controlì at all limit it to operation inside a batch or scriptì language. A special set of Z-System commands can test a wideì range of conditions, and the tests can be nested to a depthì of eight levels. Command Processor Shells If you do not want to deal with the operating system atì the command level or if you want to have a command processorì with extended features, the Z-System shell facility allowsì you to install substitute user interfaces of your own choiceì at will. They can even be nested within each other. Shells come in two common varieties: menu shells andì history shells. The menu interfaces allow the user to pickì tasks with single keystrokes and have the shell programì generate the complex sequences of commands required toì perform those tasks. The menu system shields the user from ì complexity, saves typing, and greatly reduces the chance ofì error. History shells are enhanced command processors thatì remember your commands and allow you to recall and editì previous command lines. I wish the Apollo Domainì minicomputer system I use at work (not to mention my DOS ì computer) had a history shell as nice as Z-System's LSH. Itì works like a wordprocessor on the command history, allowingì searching and extensive editing. What If You Make a Mistake This is one of the other areas in which most operatingì systems behave in an abominably primitive manner. When youì issue a command that cannot be performed, they just issue anì error message and then dump you back to square one. Oftenì you are not even told what sort of error occurred (considerì DOS's wonderfully helpful "bad command" message). The Z-System behaves in a civilized manner under theseì circumstances. When an error occurs, the command processorì turns the bad command line over to a user-specified errorì handler. The most sophisticated error handlers allow theì operator to edit the command and thus recover easily fromì typing mistakes. The system environment even contains an error type, whichì the error handler can use to give you more specificì information about what went wrong. It may be the familiarì error of a COM file that could not be found, but there areì many other possible causes for the difficulty. A file that ì you specified as an argument might not have been foundì (e.g., "TYPE FILENAM" when you meant "TYPE FILENAME"), orì you may have specified an ambiguous file name to a programì that cannot accept one (e.g., "TYPE *.DOC"). System Security Like minicomputer and mainframe operating systems, the Z¡ System is a secure operating system. This means that it hasì mechanisms for limiting what any particular user can do orì get access to. Commands that perform dangerous operationsì (such as erasing, copying, or renaming files) can be ì disabled when ordinary users are operating the system butì enabled when a privileged user is at work. Areas of yourì disk can be restricted from access for storage ofì confidential or other sensitive information. These securityì features come in very handy in the implementation of aì remote access system or bulletin board. Summary To sum it up, the goal of the Z-System is to provide anì operating environment that can be tailored extensively toì user preferences and that can be made to handle on its ownì and automatically as many computational details as it can,ì leaving the user free to concentrate solely on those ì aspects of computer operation that require humanì intelligence. Z-System, The State of the CP/M Art =================================== Now that you've seen the remarkable features of the Z¡ System, you might be curious about how it can be installedì on your CP/M computer. In this regard, the most spectacularì step in the evolution of Z-System took place about threeì years ago. At that time some major programming breakthroughs ì made it possible to configure and install the Z-System as ifì it were an application program running on the CP/M computer. ì Before that, you really had to be a rather skilled assemblyì language programmer to get Z-System running. The new Z-System comes in two flavors: NZCOM forì computers that use version 2.2 of CP/M and Z3PLUS forì computers running CP/M-Plus. Joe Wright, Bridger Mitchell,ì and I were the main developers. NZCOM and Z3PLUS embody, I believe, some of the mostì exciting and remarkable developments in the history ofì microcomputer operating systems. With all the microcomputersì I have had experience with, the operating system has been aì static entity. You boot up the computer, and there you haveì the operating system, fixed and immutable. Few computersì offer more than one operating system. With those that do,ì changing the operating system usually requires rebooting andì starting over. And never do you, the user, get to define theì characteristics of the operating system. You just take whatì the manufacturer decides to give you. With NZCOM and Z3PLUS the operating system becomes aì flexible tool just like an application program. You canì change operating system configurations at any time, evenì right in the middle of a multiple command line sequence. Youì can do it manually, or alias scripts can do it ì automatically in response to conditions in the system! You can change the whole operating system or just a partì of it. Would you like a different command processor? Noì problem. With a simple command, NZCOM or Z3PLUS will loadì another one. No assembly or configuration is required. Ifì you want to experiment with a new disk operating systemì (BDOS), NZCOM can load a new one in a jiffy. This makes forì a whole new world of flexibility and adaptability, learningì and experimentation. Do you need more memory to run a big application program? ì Fine. While that application is running, just load a smallì operating system without some of the bells and whistles. ì Then, after that task is finished, go back to the big systemì with named directories, lots of resident commands, orì special input/output facilities (such as keyboard redefinersì or redirection of screen or printer output to disk). Untilì you try NZCOM or Z3PLUS, it is hard to imagine how easy itì is to do these things. Sources of Support ================== Here are three magazines that provide significant CP/Mì support. By reading them you will learn about sources forì public-domain software (both by modem and on disk) and aboutì vendors who sell CP/M commercial software (a vendor listing,ì CPMSRC.LST, posted on bulletin boards runs to 15 printedì pages). The major, professional publication with strong coverageì of Z-System and CP/M is "The Computer Journal." Its sixì issues per year have a broad hobbyist focus, with articlesì on several operating systems, programming languages,ì embedded controllers, hardware projects, and many otherì topics. The Computer Journal ($18/yr) P.O. Box 12 S. Plainfield, NJ 07080-0012 voice: 908-755-6186 modem (Z-Node #32): 908-754-9067 on GEnie as $TCJ Two other, more informal magazines of interest to the 8-bitì community are: The Z-Letter ($15/yr) Lambda Software Publishing 720 S. Second Street San Jose, CA 95112 voice: 408-293-5176 Eight Bits and Change ($15/yr) Small Computer Support 24 East Cedar Street Newington, CT 06111 voice: 203-666-3139 modem (Z-Node #12): 203-665-1100.