The History of CP/M

THE EVOLUTION OF AN INDUSTRY:
ONE PERSON'S VIEWPOINT

published in "Dr. Dobb's Journal of Computer Calisthenics & Orthodontia",
Vol.5, No.1, (January 1980) (number 41), page 6-7

BY GARY A. KILDALL
Digital Research
P.O. Box 579
Pacific Grove, California 93950

1973. . .

I was sitting quietly at my desk when Masatoshi Shima
hurried into my office at Intel and asked me to follow him to
his laboratory down the hall. In the middle of his work bench,
among the typical snaggle of jumpers, oscilloscopes and multi-
meters, sat a binocular microscope with spider- leg probes,
all of which were subjecting a minute piece of silicon to help-
less investigation. I peered through the microscope at the en-
larged regular patterns with particular interest. As a consult-
ant, my job was to design and develop certain software tools
for Intel. One was Interp/80, a program which simulated
Intel's newly evolved 8080 microprocessor to be used by Intel
customers on timesharing systems. As I searched for some-
thing recognizable, I hoped my simulat ion resembled the
operation of Shima's first 8080 chip which had finally come to
life.

My proposal to Intel had been simple: I would provide
them with a language, called PL/M, to replace serious systems
programming in assembly language. The compi ler would
first be written in FORTRAN for operation on timesharing
computers and "cross compile" to the eight-bit processors.
Next, we would write a PL/M compiler in PL/M and "boot-
strap" from the timesharing computer to a resident compiler
operating on Intel's new Intellec-8 development system. The
first part was complete. PL/M cross compilers and Interp
simulators were implemented for the now-best- forgotten
8008, as well as the 8080. Programs had been written and
tested by Intel's software group, consisting of myself and two
other people, and we were ready for the real machine. Things
were going well: the resident compi ler would be the next
step.

Unfortunately, nearly all small computer systems in 1973
used paper tape as the backup storage device, with the ubiqui-
tous model 33 Teletype serving as the nerve-shattering I/O
device. It was readily apparent that resident development
systems could not compete with timesharing services when
considering throughput, resources, and services. Still the
notion of a personal computer for software development in-
terested everyone.

I became intrigued with a new device, called a floppy disk,
which, though designed by IBM to replace punched cards,
appeared to have much greater potential. The device was
ideal: over 3,000 times the data rate of a Teletype, each $7
diskette could randomly access the equivalent of 2000
feet of paper tape. Best of all, the drive was priced at a low
$500. Due to a slight problem of undercapitali7ation, I found
this incredibly low price still a bit high. At that time, a
smallish company called Shugart Associates was in
operation a few miles up the road from Intel. Dave Scott,
then marketing manager at Shugart Associates, donated one
of their 10,000- hour test drives to the cause, complete with
worn-out bearings and a bear ing repair kit . It was only
later , as I sat in my office at home, staring at the naked
disk drive, that I realized I had no cabinet, no cables, no
power supplies, no controller, and most distressing of all, no
hardware design experience. To make matters worse, no
controllers were commercially available, even if I could
afford one.

After several abortive attempts at constructing an inter-
face to my Intellec-8, it became readily apparent that my
efforts would be better directed toward the software
aspects.

Between projects I put together the first CP/M file system,
designed to support a resident PL/M compiler. The timesharing
version of PL/M, along with the Interp simulator, allowed me to
develop and checkout the various file operations to the level of
primitive disk I/O. A simulation is, after all, just a simulation, and
the inability to make that 10,000 hour drive work for just one
more hour was frustrating.

Shortly thereafter, in the fall of 1974, John Torode became
interested in the project. I offered as much moral support as
possible while John worked through the aberrations of the IBM
standard to complete one of my aborted controllers. Our first
controller was a beautiful rat's nest of wirewraps, boards and
cables (well, at least it was beautiful to us!) which, by good
fortune, often performed seeks, reads, and writes just as
requested. For agonizing minutes, we loaded the CP/M machine
code through the paper tape reader into the Intellec-8 memory.
To our amazement, the disk system went through its initialization
and printed the CP/M prompt at the Teletype.

Anyone who has brought -up CP/M on a homebuilt computer
has felt this moment of elation. A myriad of connections are
properly closed; bits are flying at lightning speeds over busses
and through circuits and program logic, to produce a single
prompt. In comparison to our paper tape devices, we had the
power of a S/370 at our fingertips. A few nervous tests confirmed
that all was working properly, so we retired for the evening to
take on the simpler task of emptying a jug of not-so-good red
wine while reconstructing battles, and speculating on the future
of our new software tool.

In the months that followed, CP/M evolved rather slowly. Intel
was experiencing enormous growth and all software development
was halted while new mangement structures were instituted. Intel
expressed no interest in CP/M, nor in continuing any resident
compiler work. Nearly two years passed before Intel again took
interest in resident software tools, with their introduction of the
ISIS operating system and later, the resident PL/M -80 compiler.
Meanwhile, John Torode redesigned and refined our original
controller and produced his first complete computer system,
marketed under his company name, Digital Systems (which later
became Digital Microsystems). The first commercial licensing of
CP/M took place in 1975 with contracts between Digital Systems
and Omron of America for use in their intelligent terminal, and
with Lawrence Livermore Laboratories where CP/M was used to
monitor programs in the Octopus network. Little attention was
paid to CP/M for about a year. In my spare time, I worked to
improve overall facilities, and added an editor, assembler, and
debugger which were predecessors of the current ED, ASM, and
DDT programs. By this time, CP/M had been adapted for four
different controllers.

In 1976, Glenn Ewing approached me with a problem: Imsai,
Incorporated, for whom Glenn consulted, had shipped a large
number of disk subsystems with a promise that an operating
system would follow. I was somewhat reluctant to adapt CP/M
 to yet another controller, and thus the notion of a
separated Basic I/O System (BIOS) evolved. In principle, the
hardware dependent portions of CP/M were concentrated in the
BIOS, thus allowing Glenn, or anyone else, to adapt CP/M to the
Imsai equipment. Imsai was subsequently licensed to distribute
CP/M version 1.3 which eventually evolved into an operating
system called IMDOS.

By coincidence, Jim Warren and I were both consulting at
Signetics Corporation during this time. Jim was then the editor
of DDJ, and pushed for sale of CP/M to the general public.
There was, at the time, a pervading paranoia among software
vendors who felt that any and all loose software would be
immediately "ripped-off' by this immoral group of computer
junkies. Jim's faith in the industry, however, led me to introduce
the CP/M 1.3 system for sale on the open market at $70 per
copy. In the months that followed, the nature of the computer
hobbyist became apparent. In most cases he was, like myself,
in the computer industry and merely wanted a personal
computer for his own endeavors. CP/M gradually gained
popularity through a "grassroots" effect and, to the amazement
of the skeptics, the rip-off factor was practically nil. A new
company called Digital Research was formed to support CP/M,
develop new products, and provide administrative functions.

It's been nearly three years since CP/M's initial introduction,
with several revisions and improvements. Although floppy disks
maintain their popularity, CP/M 2.0 is now offerred to manage
larger capacity hard disks which are becoming more readily
available. Customer needs and demands have also led to the
recent introduction of MP/M, a CP/M compatible multiterminal
multiprogramming system for more sophisticated applications.

More important, however, is that CP/M provides a manufacturer
independent basis for an evolving software market. We all know
that software is expensive to develop and support, with numbers
quoted in the hundreds of thousands of dollars over the product
lifetime. In a classical computer marketplace, these costs are
amortized over a few installations, resulting in seemingly
outrageous prices. Active CP/M users, however, number in the tens
of thousands and can be reached through any number of popular
magazines. Thus, marketeers reduce their prices substantially to
interest a much larger customer base. Software is sold profitably as
an independent commodity by a large number of responsible
companies, and the benefits to the consumer are clear. Competition
forces low prices and quality control, with selection among a wide
variety of software products. Currently, CP/M compatible products
range from word processing programs through business systems to
a variety of language processors for BASIC, FORTRAN, COBOL,
PASCAL, and others. All are priced in the $100 to $700 range. The
future is, without doubt, optimistic for producers and customers
alike.