TDOS8.WS4
---------
- "For Networks and Multi-user Systems -- TurboDOS"
Ron Fowler
"Microsystems", Vol.5, No.8, August 1984, p.58
(Retyped by Emmanuel ROCHE.)
Gone are the days when simple operating systems satisfied the needs of most
small-system users. Once written primarily to satisfy the relatively modest
requirements of hobbyists and experimenters, microcomputer operating systems
are now designed for performance, with special concern for providing maximum
versatility to the user.
One such operating system is TurboDOS, a product of Software 2000, Inc.
Written originally for the Zilog Z-80 (and recently converted for the Intel
8088/8086 family), this package offers a high degree of CP/M compatibility,
multi-tasking background processing, powerful networking capability, built-in
communications facilities, print spooling, and much more.
This article will take an in-depth look at this powerful system: what you can
expect to gain by using TurboDOS, and what (if anything) you might lose by
giving up CP/M in favor of TurboDOS. We will examine the TurboDOS operating
system and its utilities in detail, and conclude with a section addressed to
the programmer or system developer interested in writing TurboDOS
applications.
(ROCHE> Unfortunately, when I read this article, 30 years later, it is obvious
that Ron Fowler had no experience of MP/M, the multi-tasking, multi-user
version of CP/M... By the way, each time that he says "CP/M", you must
understand: "CP/M 2.2". TurboDOS is, in fact, a multi-processor version of
MP/M. That's why it is more compatible with MP/M than with CP/M (2.2)! Poor
Ron Fowler, not knowing MP/M, is often ecstatic by the capabilities of
TurboDOS, which are exactly (except multiple processors) those of MP/M...)
Background
----------
Much of the information presented here is based on my own custom
implementation of TurboDOS Version 1.3. The evaluation copy of the software
was provided courtesy of North Star Computers, Inc. North Star provides a full
implementation for their own hardware, and offers it bundled with Turbo-Plus,
a TurboDOS enhancement package (which I hope to review in a future article).
While Version 1.3 of TurboDOS provides Intel 8088 compatibility, this
discussion is limited to the Zilog Z-80 version. The evaluation system is a
networked version, interconnecting a Zilog Z-80-based S-100 Bus system with a
disk-less single-board Z-80 computer, through Intel 8255 PIO chips in each
computer. Figure 0 is a schematic of the circuit used to interconnect the 2
systems.
Figure 0. Two-computer network interface circuit
The S-100 Bus system consists of an Integrand mainframe housing a Delta
Products 4-MHz Z-80 CPU, 128K of CompuPro memory, and various I/O boards.
Overview
--------
TurboDOS is structured in a 2/3 arrangement: the main body of the TurboDOS
operating system is analogous to CP/M's CCP and BDOS. This portion is machine-
independent, and is supplied as a group of Microsoft-format REL (relocatable
machine code) files. The remainder of the system is similar to CP/M's BIOS,
and consists of a collection of *DEVICE DRIVERS* (for such things as disk
drives, printers, and network communications). These driver modules are
written by the system integrator; if you purchase a packaged system, these
drivers are already written for you.
The modular design of the TurboDOS operating system allows it to be configured
in an almost infinite variety of forms. Table 1 lists a number of the more
commonly-used modules.
Table 1. Common TurboDOS modules
(NOTE: Modules denoted by an asterisk (*) after the module names are resident
processes.)
Name Function
---- --------
LCLUSR* Supports the Transient Program Area
LCLMSG Contains the system error messages
CMDINT Command line interpreter, similar to CP/M's CCP
AUTLOG Supports COLDSTRT.AUT and WARMSTRT.AUT files
NETSVC* Services network requests. Necessary only in processors that provide
facilities to the network (servers)
NETREQ Makes requests of the network
NETTBL Defines network topology from viewpoint of the local node
DSPOOL* Printer de-spooler (background print)
FLUSHR* Periodically flushes disk buffers
OSNTRY Decodes system calls (C-functions and T-functions)
FILMGR Handles the local file system.
Nodes without disk storage do not require this module.
FILLOK Handles file interlocks
FFOMGR Handles the special FIFO files
FASLOD Fast program-load optimizer
BUFMGR Manages the disk buffers
DSKTBL Defines the available disk drives (local and remote)
CPMSUP Special support for CP/M.
Makes TurboDOS operating system more CP/M-compatible.
CONMGR Handles all console I/O
CONTBL Connects CONMGR to hardware console driver module(s)
DOMGR Handles batch commands
LSTMGR Handles printer output
SPOOLR Handles background spooled-print functions, as well as routine printer
output over the network
RTCMGR Maintains system date and time (real-time clock)
BNKMGR Banked memory support
DSPCHR Multi-tasking kernel; controls CPU dispatching between competing
processes, as well as synchronization and inter-process communications
DSPSGL Special "null" dispatcher; allows a non-multi-task version of TurboDOS
to be created
MEMMGR Controls dynamic allocation of memory
OSLOAD Special module used to create a loader program
COMSUB Common subroutines needed in all versions of TurboDOS
Each major function is isolated in its own module, many of which can be added
to and deleted from the TurboDOS operating system by the user (ROCHE> ? A
*USER* fine tuning a Disk Operating System?), thus providing the ability to
add or subtract functionality. For example, the SPOOLR module contains the
necessary code to implement the TurboDOS print spooling function (described
later). By deleting this module in systems that do not require print spooling
(e.g., single-user systems), the TurboDOS operating system can be made
smaller, allowing more room for disk buffers and transient programs.
Flexible as this assortment of modules may be, it would be demanding a lot to
ask all users to build their own TurboDOS operating system. To avoid this,
TurboDOS is packaged with a number of "standard" versions (Table 2), each
providing a commonly-required configuration.
Table 2. Standard TurboDOS configuration packages
Name Function
---- --------
STDLOADR Cold-start system loader
STDSINGL Single-user version, no spooling
STDSPOOL Single-user version with spooling
STDMASTR Network master
STDSLAVE Network slave without local disks
STDSLAVX Network slave with local disks
(ROCHE> So, The first 3 versions correspond to CP/M, and the last 3 versions
to MP/M. Note the emphasis on spooling. In fact, Digital Research was selling
one DESPOOL program for CP/M Versions 1 and 2, but it only ran reliably on
DRI's Intel MDS-800 microcomputers...)
The system may be configured (and reconfigured) conveniently by using GEN.COM,
the supplied system generation utility. This program is, in fact, a
sophisticated linkage editor that takes its commands from disk files,
providing a high degree of automation in the system generation process. An
additional file (called a PAR file) can be specified to GEN.COM. The PAR file
references, *BY NAME*, parameters within the system. It is a powerful concept:
you can restructure major portions of the system (such as the network
definition tables, disk assignment tables, command-search paths, and many
others) merely by editing the PAR file and regenerating the system.
Most implementations of TurboDOS provide for a boot PROM, allowing the system
to start up automatically at power-on. The boot PROM contains just enough code
to load a file named OSLOAD.COM into the program area. OSLOAD then brings in
the rest of the TurboDOS operating system. My own implementation boots from
CP/M, running OSLOAD as a CP/M transient program. This suits my particular
needs better than setting up a boot PROM -- and, incidentally, illustrates the
versatility of TurboDOS.
When the TurboDOS operating system start up, it prints a sign-on message,
followed by the system prompt. This is where TurboDOS begins to differ from
standard CP/M: the prompt contains the user number, as well as the drive name.
(TurboDOS supports 32 user numbers -- twice as many as CP/M; and the familiar
angle bracket prompt character of CP/M is replaced with a curly bracket:
"A}".)
Depending on how the system is set up, it may be necessary to *LOG IN* before
any useful work can begin. A utility, LOGON.COM, is provided for this purpose,
and another, LOGOFF.COM, is used to terminate the session. TurboDOS may,
optionally, be instructed to maintain a file of logons and logoffs, and
require that a password be specified at login. Passwords are maintained in a
special user accounts file maintained with a text editor. Additional security
allows logon to be restricted to a single user area (this restriction is
specified in the user accounts file). Another login option provides for
privileged logins (non-privileged logins may not change user areas, and
several of the supplied utilities will function only for privileged logins).
The rhythm of this system is a bit different from that of CP/M. For example,
there is no warm boot, since the entire TurboDOS operating system remains in
memory at all times. (CP/M 2.2, of course, allows the Console Command
Processor to be overwritten by a user program, thus requiring that a portion
of the CP/M 2.2 operating system be read back in from disk when a program
terminates) (ROCHE> CP/M Plus ("CP/M Version 3" in the USA), launched in 1983
(so, one year before this article), is a single-user version of MP/M... So,
since it supports "banked memory", the CCP is reloaded instantly from memory.
Each time CP/M Version 2 was spending too much time reading the floppy disk,
the data was stored in memory. 2 examples: the CCP and the directory. That's
why CP/M Plus, in a good implementation, is much faster than CP/M 2.2 running
on the same hardware.)
Additionally, there are no built-in commands; all commands are loaded as
transient programs from the disk. Hence, functions such as ERASE and RENAME
take a bit longer to complete than their CP/M 2.2 counterparts, because time
is needed to load them. Most of the utilities, however, make up for this in
expanded power and versatility, as we shall see. In any case, if a hard disk
is used, the extra time is so small as to be unnoticeable.
From the command level, TurboDOS works similarly to CP/M in that commands are
typed into the system, and the specified files are executed as transient
programs. If, however, your TurboDOS is part of a network, the programs and
files that you use are not necessarily located on your local computer (in
fact, your local computer may not even have any storage facilities (disk
drives) at all!). This networking capability is one of the strongest features
of TurboDOS, and we will examine that aspect of the system in detail later.
CP/M compatibility
------------------
TurboDOS is compatible with almost all CP/M programs. There are only a few
CP/M programs that I have seen that do not work properly under TurboDOS --
mostly public domain utilities that access some of the more obscure BDOS
system calls (7, 8, 24, 28, 29, 31, and 100-107). However, TurboDOS may be
installed with an optional CP/M-support module that will simulate these
missing functions.
Another incompatibility involves CP/M's SUBMIT processing: I am aware of
several commercial packages that make use of CP/M 2.2's special $$$.SUB file
for batch-command processing, and that do not work under TurboDOS because the
$$$.SUB file is not processed. Another optional module is supplied, that
modifies the TurboDOS batch function to emulate CP/M 2.2 more closely (but at
the expense of slowing down DO file processing). The packages mentioned do
work properly under TurboDOS if this module is installed.
Multi-tasking the CPU
---------------------
Beginning a more detailed study of TurboDOS, one of the first things that we
should note is that it can execute more than one task at a time; this
capability is usually referred to as *MULTI-TASKING*. (ROCHE> And MP/M, the
multi-user, multi-tasking version of CP/M, had done it for at least 5 years
when this article was written...)
Integral to the concept of multi-tasking is the *RESIDENT PROCESS*. A resident
process is a program that executes within the system; under TurboDOS, resident
processes are physically attached to the operating system, but logically
maintained outside of it. (That is to say: they perform their task by
executing operating system calls, in the same way that user programs do. The
difference is that user programs are transient in nature, while resident
processes are always present.)
At any given time, a process may be in any of 3 states: ready, running or
suspended. A running process is one that is currently executing on the CPU; a
ready process is one that is waiting to execute (but otherwise ready). A
suspended process (sometimes referred to as "blocked") is a process that is
waiting for some event to happen, or waiting for a period of time to expire.
(TurboDOS provides a system call that allows a process to delay execution for
a fixed time interval.)
The suspended state is perhaps the most significant. A process that is
suspended is "stacked" on one of a number of special lists (called
"semaphores"), and thus does not slow down the system by consuming CPU cycles.
At any given time, most processes will be in this suspended state. Hence, user
programs that are CPU-intensive (i.e., spend most of their time processing
data rather than waiting on I/O devices) run nearly as fast as they would on a
single-task system.
A number of "background" processes, present in each CPU running TurboDOS,
perform such actions as monitoring the network, flushing disk drive buffers
periodically, etc. Additionally, user-written resident processes are
supported; any such process is physically part of the TurboDOS operating
system, and must be added to TurboDOS when the operating system is generated.
Banking the system
------------------
TurboDOS makes good use of bank-selectable memory. When more than one bank is
available, most of TurboDOS resides in Bank 0, while transient programs
execute from Bank 1. (ROCHE> Exactly like CP/M Plus, the single-user version
of MP/M, launched one year before this article...) Since a full-featured
network-master version of TurboDOS exceeds 24K in size, this frees up a lot of
program area. (ROCHE> That's why MP/M used banked memory, since MP/M was a
multi-user version of CP/M. So, each user wanted to have its own TPA, and most
CP/M program wanted as much RAM as possible... So, the only technical solution
was to provide "banks" of memory to each user.)
Banked systems are often measured by the amount of *COMMON MEMORY* that they
consume. Common memory is a section of memory (usually located physically at
the top of the address space) that is always present within the CPU's address
space, regardless of which memory bank is switched in. Since the Zilog Z-80
CPU is limited to 64K of total address space, it is obvious that the common-
memory requirement increases at the expense of the banked segments, and thus
at the expense of memory available to transient programs (in the case
of TurboDOS, at the expense of the allowable size of the operating system).
The only portion of TurboDOS that *MUST* remain in common memory is a small
inter-bank communications module, plus some portions of the interrupt-service
routines. (ROCHE> Exactly like MP/M and CP/M Plus...) Thus, the amount of
transient program area (TPA) available is 63K, even if banked memory hardware
allows bank switching only on 4K or 16K boundaries. (ROCHE> Nothing news,
here. There is even a version of CP/M 2.2 for the Epson QX-10 having a 63.5K
TPA!...)
A utility program, BANK.COM, allows the TurboDOS operating system to be
switched between banked and non-banked mode. When non-banked mode is selected,
programs must share Bank 0 with the operating system.
Disk drives and files
---------------------
TurboDOS supports file sizes of up to 32MB (ROCHE> Like CP/M Plus...) and a
disk drive capacity of up to 134MB (ROCHE> CP/M Plus: 512MB... Of course,
compared to the 8MB of CP/M 2.2, this appeared to be an improvement... Except
that CP/M Plus had been launched by Digital Research one year earlier!...)
Obviously, such large drives will have a lot of files, and will need a lot of
seek time during such operations as file opens, directory searches, etc.
(ROCHE> That's why directories are cached in CP/M Plus.) In an effort to
decrease this time, TurboDOS supports a special directory format called a
*HASHED DIRECTORY*. (ROCHE> MP/M and CP/M Plus did not go this way.) A disk
directory may, at any time, be restructured as a hashed directory (although
the opposite is not true) by running a program named FIXDIR. (ROCHE> CP/M Plus
has something roughly similar, INITDIR.COM, which restructures the directory
to add date and time stamping of files.) Although hashing the directory made
little difference on my small-capacity floppy disks, a hardware dealer I have
worked with (who sells TurboDOS on IMS systems) reports a dramatic speed
increase on his 40MB hard disk systems. (ROCHE> I am not surprised. Me, from
experience, I only use INITDIR on floppy disks, since it consumes 1/4th of the
directory. On the hard disk, I simply type the date and time at the head of
the files.)
Another technique used by TurboDOS to increase performance is disk buffering.
(ROCHE> Called "disk caching" in CP/M Plus.) The system contains a built-in
buffer manager; moreover, a utility program supplied with the TurboDOS
operating system, BUFFERS.COM, lets you change the size of each disk buffer
and the number of buffers *WHILE THE SYSTEM IS RUNNING*. (ROCHE> Under CP/M
Plus, this is done at system generation time, with GENCPM, by the system
implementer.) These buffers are taken "off the top" of the transient program
area (TPA) (in unbanked versions of TurboDOS). If you are going to run small,
disk-bound programs, you can set up a large number of buffers, and increase
disk access speed. Conversely, memory-hungry programs (such as WordStar)
should be run with a small number of buffers, to provide as much memory as
possible. (ROCHE> Well, with "banks" of memory, each user has its own 64K of
memory...)
(I should point out that, while directory hashing made little performance
difference in my system, increasing the number of disk buffers in the system
increased disk throughput dramatically.) (ROCHE> That's why, after tests,
Digital Research added disk caching to CP/M Plus.)
Systems using banked memory may set up most of the unused part of Bank 0 as
disk buffer space, and not affect program memory space at all.
A fast file-load function supplies yet a 3rd performance increase: generally
used by the Command Interpreter (the portion of the TurboDOS operating system
that processes user command lines), this module allows a section of memory to
be loaded in the fastest manner possible. It works by scanning the disk
allocation map, detecting sequentially-allocated segments, and loading these
segments at the fastest transfer rate of the disk controller. (ROCHE> Under
CP/M Plus, the CCP is reloaded from a system Bank, so it is just a memory
transfer, and using the "Multi-Sector Count", allowing up to 16K to be
read/written in one shot...)
File attributes
---------------
TurboDOS expands on the file attributes employed by CP/M. (ROCHE> ???) The
CP/M "SYSTEM" attribute is replaced by the "GLOBAL" attribute. Files resident
in User area 0 and tagged as GLOBAL are accessible from any user area, thus
circumventing the need to duplicate frequently-used files in each user area of
the disk. (ROCHE> Under CP/M 2.2! But MP/M had been available for at least 5
years when this article was written, and CP/M Plus one year!) This global
access applies equally to files that are accessed by application programs
(such as WordStar's overlay files), or chained BASIC programs.
ARCHIVE is another (ROCHE> CP/M...) file attribute that saves time and space
when backing up files. New files are created with the ARCHIVE attribute off.
When a file is backed up using the COPY program, the ARCHIVE bit is set; when
a file is changed (extended, or written to with a random write), TurboDOS
resets the ARCHIVE attribute. COPY can be instructed not to copy files that
have been archived and have not been modified since. This process is called
"incremental backup". (ROCHE> And is provided by CP/M Plus' PIP...)
The final "new" file attribute is FIFO (ROCHE> This is specific to TurboDOS.);
it defines a special type of file accessed using a "first-in, first-out"
(FIFO) technique. FIFO files are accessed from programs like any other file,
except that sequentially-written records are appended at the end of the file,
and sequential reads are taken from the beginning. Moreover, a FIFO file may
be declared as an in-memory file (accessed much faster, since it really does
not exist on disk at all; this limits the size of the file, however, to
available memory.) (ROCHE> Most CP/M Plus implementations have a RAMdisk, so
the limit is 32MB, in this case.) This whole scheme provides a very handy
technique for passing data between background processes, and between programs
executing on different processors. Since a FIFO file can be made to "suspend"
(deactivate) a process reading the FIFO file when it is empty, it is easy to
visualize a background process that only "comes alive" when a program posts a
record to a file monitored by the background process.
Two special utilities are provided to work with FIFO files: SEND and RECEIVE.
SEND is invoked with a FIFO filename and a text string to place in the FIFO.
RECEIVE takes only a FIFO filename; it reads one record from the FIFO file
(thus deleting the record) and displays it. Together, these 2 utilities may be
used to form a rudimentary mail facility between users. (ROCHE> Better to use
CP/NET, which has been available for years...)
File interlocks
---------------
TurboDOS features file and record lockouts, since it supports background
processes that may access files at the same time as foreground processes. In
fact, network support for shared files requires at least one such process in
each file system offering file resources to the network. Interlocks are used
to coordinate file accessing by multiple simultaneous processes and necessary,
for example, when an update program must replace an inventory item's wholesale
and retail price fields. With no coordination, a querying program might read
the record sometime after the update program has begun writing new data, but
before the write is complete. Hence, the querying program reads inconsistent
data. With record locking capability, however, the update program can obtain
exclusive access to the record, "locking out" any other process that may be
attempting to access the same record.
File lockouts under TurboDOS may be configured for strict MP/M compatibility;
thus, existing programs written for MP/M's record-locking techniques (ROCHE>
Like Digital Research's Access Manager...) will work correctly under TurboDOS
(ROCHE> Fortunately, since TurboDOS is a multi-processor version of MP/M.
Hence the need to be compatible with its parent. It is the classical "chicken
and egg" problem.) Alternatively, a set of compatibility flags is available
(during system generation) to change certain rules, providing a number of new
modes not previously available under MP/M. (ROCHE> Modes which disappeared
with TurboDOS, while CP/M is still alive, 30 years later...)
Networking
----------
TurboDOS provides a plethora of features, facilities, and utilities, but, to
me, the single most outstanding one is its built-in networking capability.
(ROCHE> Never heard of MP/M, launched 5 years earlier by Digital Research?
Never seen the advertisements for CP/NET in computer magazines? Why do you
think that TurboDOS is compatible with MP/M? For pleasure?) Multiple computers
running TurboDOS may be interconnected and share such relatively expensive
peripherals as disk drives, printers, plotters, etc.
In this discussion, I will use the terms "node","CPU" and "processor"
interchangeably. (ROCHE> Not a good thing. It shows that the concept of a
network is still a novelty for you. You should have read the MP/M guides
published several years earlier...) Generally, a node can be thought of as a
workstation containing a CPU, memory, a network interface, and (optionally) a
terminal, disk drives, and printers. A node is attached to the network via one
or more connection points. It usually has some peripherals, but does not
*REQUIRE* any.
Two other terms will be used to refer to processors on the network: *MASTER*
(or *SERVER*) and *SLAVE* (or *SATELLITE*). Generally, a server processor
provides resources to the network (such as disk storage and/or printers),
while satellites do not. If satellites have local disks, these can also be
available to the network if the satellite contains the network service module
(NETSVC).
First, it is important to note that TurboDOS does not support multiple users
on a single CPU. (ROCHE> Yes, since TurboDOS is a multi-processor version of
MP/M.) The philosophy, here, is that, since processors and memory are
relatively cheap, why attempt to split up a hundred dollars or so in CPU and
memory hardware when each user can have his own CPU and memory, and suffer
none of the processing delays that are so severe in such operating systems as
MP/M and OASIS? (ROCHE> Good question. By the way, why did TurboDOS
disappear, while MP/M and OASIS are still running, 30 years later, under
emulators on the Internet?)
This concept works, and works well. (ROCHE> You should tell Intel, which never
managed to make its 8086 works this way. I cannot resist mentioning the
following, taken from "Chapter 1: Introduction" of the "Intel 8088/8086 Family
User's Manual", October 1979 (Yes, 5 years *EARLIER*!), page 1-1:
"The 8086 family architecture is characterized by 2 major principles:
1. System functions are distributed among specialized components.
2. Multi-processing capabilities are inherent in the hardware.
3. A hierarchical bus organization provides for the complex data flows
required by high-performance systems without burdening simpler systems
with unneeded capabilities."
This was written in 1979, for a CPU running at 4-MHZ. Today, *45 YEARS LATER*,
Intel has not been able to produce even a single computer using those
"principles"... So, why did Intel, the richest microcomputer company in the
world, never managed to do it, while Software 2000, Inc. (e.g., Mike Busch and
Ron Raikes), did it? Was the Zilog Z-80 CPU so much better than the Intel 8088
of the IBM Clown?)
Each user has full use of his own CPU; delays are generally noticeable only
when shared disk drives are simultaneously accessed by multiple network users.
(Even these delays can be abated by using faster drives with more
sophisticated seek mechanisms -- a cost that can be justified more easily with
TurboDOS, since these expensive peripherals are more easily shared among all
the users.)
TurboDOS supports just about any kind of local network, ranging from simple
implementation involving 2 computers (liked through,say, an RS-232-C channel),
to sophisticated structures with many processors sharing resources over high-
speed data channels. The actual network structure is defined by the system
designer, and implemented in the network driver modules. These modules
constitute what is known in network vernacular as the "physical layer"; they
control the hardware that interconnects the computers.
TurboDOS defines the network as being composed of *CIRCUITS* (which can be
better visualized as a cluster of nodes). A circuit may be composed of up to
255 nodes. Further, there may be up to 255 interconnected circuits in a full
TurboDOS system, allowing for a total of up to 65,535 total workstations in a
TurboDOS network.
The unit of information exchange among network nodes in the *NETWORK MESSAGE*.
This message is a packet of data, containing source and destination node
addresses, byte length and other overhead, as well as the actual data itself
(which may be a disk record, a file control block (FCB), or perhaps a block of
characters to be sent to a printer).
A "forwarding" table may be specified in each node, allowing messages to be
sent between network nodes that are not, themselves, directly connected.
One of the most common techniques that I have seen for implementing a network
with TurboDOS involves S-100 Bus single-board computers. Generally, one
"master" CPU is provided (to control access to disk drives, printers, etc.),
and one or more "slave" processors are placed on the same S-100 Bus as the
master (often these slaves have no local storage of their own but, instead,
rely on the master to provide storage. The user will see the master's disk
drives as if they were connected to his own CPU.) Typically, high-speed
parallel-port channels are provided to allow network transfers at near-bus
speeds. One such system will, generally, be a circuit in itself; multiple
systems may, then, be interconnected, forming a multiple-circuit network.
Figure 1. A typical network
An example should help tie this all together. In Figure 1, we have 2 network
circuits that are relatively independent. Each circuit has a master and
several slaves, as well as disk drives and a printer. Master-to-slave
communication is through a high-speed parallel bus. Master-to-master
communication is through a Local Area Network (LAN) interface and cable. Note
that slave nodes do not have any local disk storage but, instead, use the
master's disk drive (this will likely be a large-capacity hard disk drive,
segmented into several smaller drives, and apportioned among the slaves).
Circuit 1 consists of 4 nodes: the master and the 3 slaves. Similarly, Circuit
2 consists of 5 nodes: the master and 4 slaves, 3 of which are connected via
modems to dial-in phone lines.
Each of the 2 masters are actually "known" on 2 circuits (their own, and the
other master's) and, thus, have 2 circuit drivers within their TurboDOS
operating systems (and 2 network addresses, as a matter of fact).
This system might be part of an overall data-gathering system where field
agents phone in information to the nodes connected to modems (Nodes 2-2, 2-3,
and 2-4); the high-speed dot-matrix printer might be used to maintain a
"running log" of these transactions. This raw information is sorted and
formatted by programs entered by an operator at the terminal located at Node
2-1 (the only "on-site" terminal in Circuit 2) and made available periodically
to Circuit 1 through the RS-232-C link between circuits, where service clerks
work at terminals, filling these orders. The finished orders are, then,
printed up in the form of invoices on the letter-quality printer located on
Circuit 1.
Thus, most information flow between the 2 circuits will take place between the
2 masters (perhaps under the control of a resident process in each). It is
possible, however, to allow communications between slaves on different
circuits, using forwarding tables contained in each slave's operating system.
This might be necessary, for example, to allow field salesmen calling into
Circuit 2 to make an inquiry about an order to a clerk working in Circuit 1.
Proper setup of the forwarding tables will allow this (in fact, the Turbo-Plus
enhancement package provides special system functions and utilities that
simplify this kind of communication).
Reconfiguring the network
-------------------------
Although the physical network is defined in network driver modules, TurboDOS
provides a lot of latitude in reallocating resources, using the previously-
mentioned GEN program. Although these resources are not *DYNAMICALLY*
changeable (that is to say: you cannot make changes while the TurboDOS
operating system is running), it is a relatively simple matter to patch the
tables, and regenerate the system.
Figure 2. Drive allocation example
An example should help to clarify this. Referring to Figure 2, we see 2
processors, named P1 and P2, each with local drives A and B. From the diagram,
you can see that each processor has a drive C, which is the opposite
processor's B drive. (These assignments are made in a table contained in each
node's copy of TurboDOS; this table is called the Disk Assignment Table, and
is usually set up in a PAR file.)
Figure 3. Allocation after regeneration
Now, let us consider changing that. Let us say that we want to delete P2's
ability to reference P1's B drive, and increase P1's available storage to
include P2's drive as P1's D. We simply make a few changes in each node's PAR
file, regenerate each TurboDOS operating system, and we have the structure
shown in Figure 3. This concept applies to other resources, such as printers
and print queues.
Printers and spooling
---------------------
Flexibility is apparent throughout the design of TurboDOS, but nowhere is this
more evident that in the facilities available to produce printed output.
Each processor may have up to 16 printers defined in its tables, and each
printer may be accessed either locally or over the network. Since TurboDOS
provides a CP/M-like environment, only one of these printers may be "current"
at any one time for any one user. A utility program, PRINT.COM, lets you
change the routing of your logical printer output, using syntax such as:
PRINT PRINTER=E (or PRINT P=E)
which selects Printer E in your local printer table. In addition, this utility
allows you to select a much more flexible form of printing: *SPOOLED
PRINTING*. (ROCHE> Ever heard of the "DESPOOL (background print utility)
Operator's Guide", Digital Research, 1979? No? It was frequently found in CP/M
Version 1.4 and Version 2.2 advertisements...)
Spooled printing reroutes your printer output: instead of going directly to
the printer, the output is routed to one of 16 *PRINT QUEUES*. A print queue
is implemented as a set of disk files, using filenames of the form: PRINT-
x.nnn, where x is the queue name (A-P, corresponding to each of the 16
possible queues) and nnn is a 3-digit number used to separate different print
jobs within a queue.
Another utility, PRINTER.COM, controls despooling of these print queues. Any
physical printer may be assigned to any of the queues with a command such as
PRINTER E QUEUE=C (to assign Printer E to the C Queue). A 3rd utility,
QUEUE.COM, allows files to be manually entered into any of the various queues.
Let us tie this all together with an example: suppose your TurboDOS operating
system has 2 printers: Printer 1 is a fast dot-matrix printer, while Printer 2
is a slower letter-quality model (remember, either printer may be attached to
our local network node, or to a remote node -- it does not matter *WHERE* the
printer to be used is actually located). Assume that we have to print several
program listings, a couple of letters, and a long report.
First, we will tackle the letters, since they will likely use single-sheet
paper, requiring a good deal of manual intervention. The command:
PRINT PRINTER=B
gives up direct access to the letter-quality printer (we must be careful,
here, to coordinate access with any other network users, since direct printing
by more than one user will result in interspersed characters in the actual
printout). Now, we fire up the word-processor program, and print each letter.
Not so different from CP/M, so far (except for the ability to switch
printers).
Now, let us tackle the program listings. We can begin to make use of print
queues, here, by entering the following commands:
PRINTER A QUEUE=A
PRINTER B QUEUE=B
Now, we have established Queue A as the queue associated with the dot-matrix
printer, and Queue B with the letter-quality printer. Now, we are ready to
print some listings. The command:
PRINT QUEUE=A
routes our printer output to Queue A; now, we can run our language translator
and begin producing the program listings. Since our output is now going to a
relatively high-speed disk file (as opposed to a slow printer), the language
translator finishes long before the first printout is complete.
In fact, the first output file does not begin printing until its associated
queue file is closed (either by the language translator terminating and
returning to the TurboDOS operating system, or by a special end-print control
sequence from the console). While the first file is printing (in the
background), we can run our language translator once more, to generate the 2nd
and 3rd listings. We might also decide to queue some existing disk files:
QUEUE MYPROG.PRN ;Q=A
QUEUE MANUAL.DOC ;Q=A
QUEUE *.UPC ;DYQ=A
(Note that the Q=A options specify which queue to send the file to. The 3rd
example illustrates queuing multiple files by specifying a wildcard filename.
Additionally, the ;DY portion specifies options. In this case, D causes each
file to be Deleted after printing, and Y causes the QUEUE program to displa(Y)
the name of each file to be queued, allowing the operator to select specified
files.)
Now, we are ready to print the letter-quality documents. The command:
PRINT QUEUE=B
switches our printer output to the queue we have previously associated with
the letter-quality printer. (It does not matter that the files that we have
already queued are still printing; they are now destined for the dot-matrix
printer, and changing the destination of our printer output no longer has any
effect on the previously-queued files.) Now, we can use our word-processor,
and send the letters and the report to the B Queue, similar to the way our
language translator output went to the A Queue.
At this point, we have 2 printers running a number of print jobs entirely in
the background, and our console is free for new work. In addition, any number
of network users can simultaneously queue files on the same printers, without
intermixing printer output.
To conclude the discussion, I must mention that there are many more print
options and features than those mentioned here; to review each of them,
however, is beyond the scope of this article.
Batch files
-----------
TurboDOS allows the execution of batch-command files in a way similar to
CP/M's SUBMIT facility, but with enhanced capabilities. The TurboDOS version
of SUBMIT is named DO.COM; specifying DO with a filename will cause the system
to begin reading its input from the file.
DO files may be nested (ROCHE> Like SUBMIT under CP/M Plus...), to any
reasonable depth (ROCHE> 128 levels under CP/M Plus.), merely by placing a DO
statement within a DO file. After the subservient DO file is executed, control
returns to the superior file at the point where processing left off.
Command-line parameters may be specified in a manner similar to CP/M's SUBMIT.
However, the parameters are referred to, in the DO file, by enclosing them in
curly brackets, rather than the dollar sign notation of CP/M. Also, the
parameters in the DO command line may be made to contain embedded spaces by
enclosing them in quotes.
A handy option within the DO file allows default parameters to be filled in by
adding a comma and a default value within the curly brackets. Consider the
following line within a DO file:
L80 {1} {2,SYSLIB}
If this DO file is invoked only with Argument 1, then the value SYSLIB is
automatically supplied as the 2nd Argument.
Another important characteristic of DO files is that they can provide input
for more than just system commands. Programs that require interactive input
will receive that input from the DO file (thus, DO combines the features of
both the CP/M 2.2 programs SUBMIT and XSUB). (ROCHE> CP/M Plus has a much
better and more powerful SUBMIT utility.)
DO is somewhat faster than CP/M 2.2's SUBMIT when no command-line parameters
are specified. Since there is no need to rewrite the DO file with parameters
filled in, DO simply informs TurboDOS to begin executing the file (SUBMIT must
always write a $$$.SUB file).
Utilities
---------
TurboDOS is supplied with a large number of utilities, some of which have
already been described. The major remaining utilities are as follows:
AUTOLOAD allows a user to set up command lines that automatically execute on
either cold or warm boot. COLDSTRT.AUT, the cold boot file, executes only
once, when the TurboDOS operating system is first started up. WARMSTRT.AUT is
executed at the completion of each transient program.
BACKUP performs a fast disk copy. It is usable only when the source and
destination diskettes are of the same format.
BATCH is useful in network environments, and uses a special FIFO file (named
BATCH.DO) to send a command line to a remote processor for execution. Remote
processors that use this facility (i.e., those which are to be available for
batch jobs) must execute the command DO BATCH via an AUToload file at system
startup.
BOOT allows the system tracks of a diskette to be copied to another diskette.
Note that TurboDOS allows 100% of the floppy disk space to be used for file
storage; however, in some implementations, the hardware demands cold-starting
from reserved system tracks.
CHANGE is used to safely allow removable disks (i.e., floppies or removable
cartridges) to be changed in a network environment. CHANGE.COM takes one or
more drive letters as arguments, and aborts with an error message if any
process has open files on the requested drive. If the requested drive is free,
CHANGE locks the drive until the user indicates that the disk has been changed
(any user trying to access the drive while it is locked will receive a disk
error message).
COPY, which was previously mentioned, allows files to be copied between disk
drives. A large number of command-line options make this an extremely
versatile file copy and archiving program.
DELETE performs the same functions as CP/M's ERA. A command-line option causes
DELETE to present each filename to be erased, and requests the operator to
confirm before deleting. (ROCHE> "The CONFIRM option informs the CP/M Plus
operating system to prompt (the user) for verification before erasing each
file that matches the filespec." CP/M Plus User's Guide, Section 5: Command
Summary, "The ERASE command".)
DIR prints a sorted directory on the screen (or, optionally, on the printer).
The display contains a lot of the information available under CP/M only
through the CP/M 2.2 STAT command (such as filesizes and disk free space). It
also includes time of day and combined size of files displayed, as well as
user-number specification.
DRIVE displays information about the disk format (similar to CP/M 2.2's STAT
DSK:).
FIFO is used to create and delete the previously-described FIFO files.
FIXDIR is a handy utility that reorganizes a disk directory. This is useful
when frequent file creations and deletions occur (especially on hard disks).
FIXDIR compacts the directory, eliminates "holes", and makes file searches
faster. Also used to convert a directory to the hashed format, or vice-versa.
(ROCHE> ??? Ron wrote "the opposite is not true" in the "Disk drives and
files" paragraph...)
FORMAT allows a diskette to be formatted in single density or in CP/M or
TurboDOS double-density format. It automatically calls VERIFY after formatting
is complete. (ROCHE> VERIFY marks all the "bad spots" of a disk. That's why it
is used after formatting the disk.)
MONITOR is the TurboDOS replacement for CP/M 2.2's DDT program. Intended
mainly for program patching, etc., it contains a save function as well as a
load function (this is necessary because TurboDOS lacks CP/M 2.2's SAVE
command). A number of other commands not found in DDT are present in MONITOR.
(ROCHE> ASM and DDT were provided with CP/M 2.2. MAC and SID were professional
versions that were available separately, at a cost.)
Noticeably lacking, however, are DDT's opcode assembler and disassembler
(ROCHE> The A and L commands.), and single-step trace functions (ROCHE> The
TRACE utility of SID.). For program debugging, DEBUG (Phoenix Software
Associates (ROCHE> Software 2000, Inc., used their PASM to assemble TurboDOS.)
or ZSID (Digital Research, Inc.) both work well under TurboDOS. (ROCHE> This
is no surprise...)
RENAME is used to change the names of files. This utility has a syntax
backward from that of CP/M. (Most people who have worked with other operating
systems claim that it is CP/M that has it backward. I am inclined to agree.)
(ROCHE> You (and them) are wrong. Demonstration: How work the opcodes of the
(real, physical) processor? You write MNEMONIC DESTINATION,SOURCE... There is
no exception to this rule! So, is the CPU behaving crazily? Another
demonstration: When you send dozens of different files to the same place. If
the destination is at the beginning of the command line, you just edit the
source specification, conveniently located at the end of the command line...
which can be reached with one single control char!) This utility has the handy
option of renaming by using wildcards. For example, the command RENAME *.BAK
*.ASM renames all BAK files to ASM (a command-line option allows you to verify
any rename that would cause an existing file of the same name to be
overwritten). (ROCHE> "If the file given by NEWNAME is already present in the
directory, RENAME displays the following message on the screen: Not renamed:
FILENAME.TYP file already exists, delete (Y/N)?" CP/M Plus User's Guide,
Section 5: Command Summary, "The RENAME command".)
SERVER has been renamed by North Star. The standard TurboDOS distributed by
most vendors refers to this utility as MASTER.COM. In any case, its purpose is
to allow a slave console to act as a terminal to the master, a function useful
for running programs in the master processor.
SET is used to set and clear file attributes; SHOW displays them. (ROCHE> Just
like MP/M and CP/M Plus...)
TYPE displays ASCII files on the console or (optionally) on the printer.
USER allows privileged logins to change the currently-logged user number. This
is one command that I wish had been built into the TurboDOS operating system.
(ROCHE> Ron ported TurboDOS Version 1.3. As far as I know, the Command
Interpreter of TurboDOS Version 1.4 recognizes the small form of changing user
numbers (1:), without the need of running the transient program USER.COM.)
VERIFY scans a disk for bad blocks, and locks them out.
Program interface
-----------------
As you would expect, TurboDOS provides a good many additional system calls for
the programmer. (ROCHE> Well, TurboDOS being a multi-processor version of
MP/M, most of them have been existing under MP/M for about 5 years...) Non-
programmers may want to skip this section.
First of all, CP/M-compatible system calls are vectored through location 5 (as
you would expect); versions of TurboDOS prior to Version 1.3 included extended
system calls vectored in the same way. (ROCHE> Like MP/M...) Recent re-
releases of CP/M and MP/M, however, have caused some conflicts with TurboDOS
extended functions. (ROCHE> ???)
To correct this problem, TurboDOS Version 1.3 moved all TurboDOS extended
system calls to location 80 (0050H). CP/M-compatible (ROCHE> Which version of
CP/M? 2 or 3?) system calls are now referred to as C-functions, and TurboDOS
extended system calls as T-functions.
Resident processes must often make system calls; they cannot call location 5
or 50H. (ROCHE> ??? Why?) Two special entry points are provided for this
purpose, and must be called symbolically. They are: OCNTRY (C-functions) and
OTNTRY (T-functions). (ROCHE> So, O means Operating system, C means CP/M, and
T means TurboDOS.) The calling conventions are, otherwise, strictly the same
as they would be for a transient program. For example, to set the DMA buffer
address, you would use the following code:
MVI C,SetDMA
LXI D,Buffer
CALL OCNTRY#
A wide range of T-functions is provided (see Table 1) for such varied things
as creating and deleting resident processes, allocating and de-allocating
memory, inter-process communications, date/time functions, extended file and
disk drive requests, and more. A few of the more interesting functions are
described here.
Communications channel support (T-functions 34-40): A full complement of
functions allows complete access to the optional communications system
(generally implemented in the form of RS-232-C drivers by the system
implementer). These functions allow such actions as send/receive character,
read status, get/set baud rate, and get/set modem controls. They also allow
the creation of system-independent communications software for TurboDOS --
something that is impossible with CP/M. (ROCHE> ??? And CP/NET, what is it
doing? It is not tied to any protocol or hardware!)
Delay process (T-function 2) circumvents the need for software timing loops.
This function allows a program (or resident process) to delay by increments as
fine as the system "tick" time (generally 1/60th of a second). (ROCHE> In the
USA. 1/50th of a second in Europe.)
Return serial number (T-function 12) returns the complete serial number of the
TurboDOS operating system. (This function can be used to discourage piracy by
keying the purchaser's TurboDOS operating system to your software package.)
Load file (T-function 15) uses the previously-described Load Optimizer to load
code segments into the program area. Handy for loading overlays.
Activate DO file (T-function 16) allows a program to begin a batch processing
job. (Compared to writing the old backward $$$.SUB file with CP/M 2.2,
starting batch jobs under TurboDOS is simple with this system call.)
Send Command Line (T-function 18) allows creation of applications such as
menus from assembly language programs. It does not work quite the same way as
MP/M's similarly-named function (ROCHE> This must be a coincidence?), however,
in that the passed Command Line is not executed immediately (as it is in MP/M)
but is, instead, deferred until the calling program terminates. You may
"stack" command lines by calling this function more than one.
Printer control functions T-functions 27-30) allow complete programmatic
access of the printer spooling and despooling mechanisms. Function 28 (signal
end-of-print) is especially handy, since it allows a queued print job to
actually begin printing.
User-defined function (T-function 41) belongs to the user, for any purpose
that he desires to write code for. It can take full advantage of the network
for communications between processors. To implement this function, you must
write your function in a module that defines the public symbol USRFCN;
register-passing conventions are described in the "TurboDOS Release 1.4 Z80
Programmer's Guide". Once the function is in place, your applications program
may communicate with it simply by calling T-function 41.
Documentation
-------------
No software evaluation can be considered complete without a look at the
documentation supplied with the package. In the case of TurboDOS, I have to
rate the documentation effort outstanding! (ROCHE> Interesting. Apparently,
not everyone thinks like you. "Many features of TurboDOS go underutilized (or
totally ignored) due to the difficulty in deciphering the manuals." and "the
manuals are indescribably bad." This opinion was published in nothing less
than the "ACM SIGSMALL Newsletter"! Reference: Vol.10, No.3, August 1984,
p.24, "The TurboDOS Operating System", Keith Bierman.)
Three manuals are provided with the Z80 TurboDOS operating system: a User's
Guide, a Z80 Programmer's Guide, and the Z80 System Implementer's Guide. Each
includes a table of contents; the System Implementer's Guide is the only
manual lacking an index.
The User's Guide begins with basics, and takes the reader through the
gradually more complex subjects of files, disks, printing, and processing,
concluding with a summary of the entire set of 35-odd utilities that are
provided with the TurboDOS operating system. The language is "gentle" and very
readable.
The Programmer's and Implementer's Guides are understandably more complex,
since they deal with subjects that are technical in nature. They are complete,
and provide sufficient information to enable the programmer to do his job.
(ROCHE> Again, Ron implemented TurboDOS Version 1.3. Version 1.4 adds the 8086
programmer's Guide and the 8086 Implementer's Guide. TurboDOS thrived when it
was written in Zilog Z-80 assembly language for S-100 Bus systems, and
disappeared when it was rewritten in the C language for the IBM PC...)
Conclusion
----------
As you see, TurboDOS provides powerful facilities for both the user and the
programmer. After more than 3 years on the market (it was first released in
April 1981) (ROCHE> So, MP/M had already been existing for 2 years when
TurboDOS appeared... Guess which is the chicken? Which is the egg?), TurboDOS
is still being continually refined. (By the time you read this, Release 1.4
should be available. This new release will feature full Intel 8088/8086
compatibility at both the slave *AND* the master level, as well as a PC DOS
emulator.) (ROCHE> Emulating MS-DOS Version 1 under TurboDOS on a S-100 Bus
system? Vade Retro, Satanas!)
I have recently obtained a Mega Z-80 system, featuring 512K bank-selectable
RAM and 27 *MEGABYTE* Winchester hard disk drive, for which I plan to do a
full master-to-master implementation of TurboDOS (complete with RAMdisk). As
"Microsystems" magazine expands its TurboDOS coverage, I hope to provide a
follow-up article on this project, as well as a review of Turbo-Plus, and (if
there is sufficient interest) a tutorial on TurboDOS implementation and
programming technique. (ROCHE> This article was the last one written by Ron
Fowler...)
EOF