Carl Sassenrath (born 1957 in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

) is an architect of

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s and

computer language A computer language is a formal language used to communicate with a computer. Types of computer languages include: * Software construction#Construction languages, Construction language – all forms of communication by which a human can Comput ...

s. He brought multitasking to

personal computer A personal computer, commonly referred to as PC or computer, is a computer designed for individual use. It is typically used for tasks such as Word processor, word processing, web browser, internet browsing, email, multimedia playback, and PC ...

s in 1985 with the creation of the

Amiga Computer Amiga is a family of personal computers produced by Commodore from 1985 until the company's bankruptcy in 1994, with production by others afterward. The original model is one of a number of mid-1980s computers with 16-bit or 16/32-bit processor ...

operating system kernel, and he is the designer of the REBOL computer language, REBOL/IOS collaboration environment, the Safeworlds AltME private messaging system, and other products. Carl was a Principal Engineer at Roku, Inc. until his retirement in November 2023.

Background

Carl Sassenrath was born in 1957 to Charles and Carolyn Sassenrath in California. His father was a

chemical engineer A chemical engineer is a professional equipped with the knowledge of chemistry and other basic sciences who works principally in the chemical industry to convert basic raw materials into a variety of Product (chemistry), products and deals with ...

involved in research and development related to petroleum refining, paper production, and air pollution control systems. In the late 1960s his family relocated from the

San Francisco Bay Area The San Francisco Bay Area, commonly known as the Bay Area, is a List of regions of California, region of California surrounding and including San Francisco Bay, and anchored by the cities of Oakland, San Francisco, and San Jose, California, S ...

to the small town of

Eureka, California Eureka ( ; Wiyot: ; Hupa: ; ) is a city and the county seat of Humboldt County, located on the North Coast of California. The city is located on U.S. Route 101 on the shores of Humboldt Bay, north of San Francisco and south of the Oreg ...

. From his early childhood Sassenrath was actively involved in electronics,

amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency radio spectrum, spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emer ...

, photography, and filmmaking. When he was 13, Sassenrath began working for

KEET Keet may refer to: * Keet, a name for some types of parakeet * Keet, a young guineafowl Guinea fowl () (or guineahen) are birds of the family Numididae in the order Galliformes. They are endemic to Africa and rank among the oldest of the gall ...

, a

PBS The Public Broadcasting Service (PBS) is an American public broadcaster and non-commercial, free-to-air television network based in Arlington, Virginia. PBS is a publicly funded nonprofit organization and the most prominent provider of educat ...

public broadcasting television station. A year later he became a

cameraman A camera operator, or depending on the context cameraman or camerawoman, is a professional operator of a film camera or video camera as part of a film crew. The term "cameraman" does not necessarily imply that a male is performing the task. ...

for

KVIQ KVIQ-LD (channel 14) is a low-power television station in Eureka, California, United States, affiliated with CBS. It is owned by Marquee Broadcasting alongside NBC affiliate KIEM-TV (channel 3). The two stations share studios on South Broadway ...

(

ABC ABC are the first three letters of the Latin script. ABC or abc may also refer to: Arts, entertainment and media Broadcasting * Aliw Broadcasting Corporation, Philippine broadcast company * American Broadcasting Company, a commercial American ...

affiliate then) and worked his way up to being

technical director A technical director (TD) is usually a senior technical person within e.g. a software company, engineering firm, film studio, theatre company or television studio. They are responsible for overseeing and coordinating all of the technical aspect ...

and director for news, commercials, and local programming. In 1980 Sassenrath graduated from the

University of California, Davis The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...

with a B.S. in EECS (

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

and

computer science Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...

). During his studies he became interested in

s, parallel processing,

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

s, and

neurophysiology Neurophysiology is a branch of physiology and neuroscience concerned with the functions of the nervous system and their mechanisms. The term ''neurophysiology'' originates from the Greek word ''νεῦρον'' ("nerve") and ''physiology'' (whic ...

. He was a teaching assistant for graduate computer language courses and a research assistant in

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...

and behavioral biology. His uncle, Dr. Julius Sassenrath, headed the educational psychology department at

UC Davis The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...

, and his aunt, Dr. Ethel Sassenrath, was one of the original researchers of THC at the

California National Primate Research Center The California National Primate Research Center (CNPRC) is a federally funded biomedical research facility, dedicated to improving human and animal health, and located on the University of California, Davis, campus. The CNPRC is part of a network ...

Career

Hewlett-Packard

During his final year at the university, Sassenrath joined

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company. It was founded by Bill Hewlett and David Packard in 1939 in a one-car garage in Palo Alto, California ...

's Computer Systems Division as a member of the Multi-Programming Executive (MPE) file system design group for

HP 3000 The HP 3000 series is a family of 16-bit computing, 16-bit and 32-bit computing, 32-bit minicomputers from Hewlett-Packard. It was designed to be the first minicomputer with full support for time-sharing in the hardware and the operating system, ...

computers. His task was to implement a

compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...

for a new type of control language called ''Outqueue''—a challenge because the language was both descriptive and procedural. A year later, Sassenrath became a member of the MPE-IV OS

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

team and later part of the HPE kernel group. While at HP Sassenrath became interested in minimizing the high complexity found in most operating systems of that time and set out to formulate his own concepts of a

microkernel In computer science, a microkernel (often abbreviated as μ-kernel) is the near-minimum amount of software that can provide the mechanisms needed to implement an operating system (OS). These mechanisms include low-level address space management, ...

-based OS. He proposed them to HP, but found the large company complacent to the "smaller OS" ideas. In late 1981 and early 1982, Sassenrath took an academic leave to do atmospheric physics research for

National Science Foundation The U.S. National Science Foundation (NSF) is an Independent agencies of the United States government#Examples of independent agencies, independent agency of the Federal government of the United States, United States federal government that su ...

Amundsen–Scott South Pole Station The Amundsen–Scott South Pole Station is a science and technology in the United States, United States scientific research station at the South Pole of the Earth. It is the List of extreme points of the United States, southernmost point under ...

. Upon returning, Sassenrath reached an agreement with HP to pursue independent research into new areas of computing, including

graphical user interface A graphical user interface, or GUI, is a form of user interface that allows user (computing), users to human–computer interaction, interact with electronic devices through Graphics, graphical icon (computing), icons and visual indicators such ...

s and

remote procedure call In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space (commonly on another computer on a shared computer network), which is written as if it were a ...

methods of distributed computing. Later in 1982, impressed by the new computing ideas being published from

Xerox PARC Future Concepts division (formerly Palo Alto Research Center, PARC and Xerox PARC) is a research and development company in Palo Alto, California. It was founded in 1969 by Jacob E. "Jack" Goldman, chief scientist of Xerox Corporation, as a div ...

, Sassenrath formed an HP project to develop the modern style of window-based

mouse A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...

-driven GUIs. The project, called ''Probus'' (for professional business workstation) was created on a prototype

Sun Microsystems Sun Microsystems, Inc., often known as Sun for short, was an American technology company that existed from 1982 to 2010 which developed and sold computers, computer components, software, and information technology services. Sun contributed sig ...

workstation borrowed from

Andy Bechtolsheim Andreas Maria Maximilian Freiherr von Mauchenheim genannt Bechtolsheim (born 30 September 1955) is a German electrical engineer, entrepreneur and investor. He co-founded Sun Microsystems in 1982 and was its chief hardware designer. he's 68th w ...

while he was at

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

. Probus clearly demonstrated the power of graphical user interfaces, and the system also incorporated

hyperlink In computing, a hyperlink, or simply a link, is a digital reference providing direct access to Data (computing), data by a user (computing), user's point and click, clicking or touchscreen, tapping. A hyperlink points to a whole document or to ...

s and early

distributed computing Distributed computing is a field of computer science that studies distributed systems, defined as computer systems whose inter-communicating components are located on different networked computers. The components of a distributed system commu ...

concepts. At HP, Sassenrath was involved with and influenced by a range of HP language projects including

Ada Ada may refer to: Arts and entertainment * '' Ada or Ardor: A Family Chronicle'', a novel by Vladimir Nabokov Film and television * Ada, a character in 1991 movie '' Armour of God II: Operation Condor'' * '' Ada... A Way of Life'', a 2008 Bollywo ...

, Pascal,

Smalltalk Smalltalk is a purely object oriented programming language (OOP) that was originally created in the 1970s for educational use, specifically for constructionist learning, but later found use in business. It was created at Xerox PARC by Learni ...

Lisp Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized Polish notation#Explanation, prefix notation. Originally specified in the late 1950s, ...

Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotl ...

, SPL, and a variety of experimental languages.

Amiga

In 1983, Carl Sassenrath joined Amiga Computer, Inc., a small startup company in

Silicon Valley Silicon Valley is a region in Northern California that is a global center for high technology and innovation. Located in the southern part of the San Francisco Bay Area, it corresponds roughly to the geographical area of the Santa Clara Valley ...

. As ''Manager of Operating Systems'' he was asked to design a new operating system for the

Amiga Amiga is a family of personal computers produced by Commodore International, Commodore from 1985 until the company's bankruptcy in 1994, with production by others afterward. The original model is one of a number of mid-1980s computers with 16-b ...

, an advanced multimedia personal computer system that later became the

. As a sophisticated computer for its day (Amiga used 28 DMA channels along with multiple

coprocessor A coprocessor is a computer processor used to supplement the functions of the primary processor (the CPU). Operations performed by the coprocessor may be floating-point arithmetic, graphics, signal processing, string processing, cryptography or ...

s), Sassenrath decided to create a

preemptive multitasking In computing, preemption is the act performed by an external scheduler — without assistance or cooperation from the task — of temporarily interrupting an executing task, with the intention of resuming it at a later time. This preemptive sc ...

within a

design. This was a novel approach for 1983 when other personal computer operating systems were single tasking such as

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

(1981) and the

Macintosh Mac is a brand of personal computers designed and marketed by Apple Inc., Apple since 1984. The name is short for Macintosh (its official name until 1999), a reference to the McIntosh (apple), McIntosh apple. The current product lineup inclu ...

(1984). The Amiga multitasking kernel was also one of the first to implement a microkernel OS methodology based on a

real-time Real-time, realtime, or real time may refer to: Computing * Real-time computing, hardware and software systems subject to a specified time constraint * Real-time clock, a computer clock that keeps track of the current time * Real-time Control Syst ...

message passing In computer science, message passing is a technique for invoking behavior (i.e., running a program) on a computer. The invoking program sends a message to a process (which may be an actor or object) and relies on that process and its supporting ...

(

inter-process communication In computer science, interprocess communication (IPC) is the sharing of data between running Process (computing), processes in a computer system. Mechanisms for IPC may be provided by an operating system. Applications which use IPC are often cat ...

) core known as Exec (for executive) with dynamically loaded libraries and devices as optional modules around the core. This design gave the Amiga OS a great extensibility and flexibility within the limited memory capacity of computers in the 1980s. Sassenrath later noted that the design came as a necessity of trying to integrate into

ROM Rom, or ROM may refer to: Biomechanics and medicine * Risk of mortality, a medical classification to estimate the likelihood of death for a patient * Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac * ...

dozens of internal libraries and devices including graphics, sound,

floppy disk A floppy disk or floppy diskette (casually referred to as a floppy, a diskette, or a disk) is a type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined with a ...

, file systems, and others. This dynamic modular method also allowed hundreds of additional modules to be added by external developers over the years. After the release of the Amiga in 1985, Sassenrath left Commodore-Amiga to pursue new programming language design ideas that he had been contemplating since his university days.

Apple Computer

In 1986, Sassenrath was recruited to Apple Computer's Advanced Technology Group (ATG) to invent the next generation of operating systems. He was part of the Aquarius project, a quad-core CPU project (simulated on Apple's own

Cray Cray Inc., a subsidiary of Hewlett Packard Enterprise, is an American supercomputer manufacturer headquartered in Seattle, Washington. It also manufactures systems for data storage and analytics. Several Cray supercomputer systems are listed ...

XMP-48) that was intended to become a 3D-based successor to the Macintosh. During that period, the C++ language had just been introduced, but Sassenrath, along with many other Apple researchers, preferred the more pure OO implementation of the

language. Working at ATG with computing legends like

Alan Kay Alan Curtis Kay (born May 17, 1940) published by the Association for Computing Machinery 2012 is an American computer scientist who pioneered work on object-oriented programming and windowing graphical user interface (GUI) design. At Xerox ...

Larry Tesler Lawrence Gordon Tesler (April 24, 1945 – February 16, 2020) was an American computer scientist who worked in the field of human–computer interaction. Tesler worked at Xerox PARC, Apple Inc., Apple, Amazon.com, Amazon, and Yahoo!. While at PA ...

Dan Ingalls Daniel Henry Holmes Ingalls Jr. (born 1944) is a pioneer of object-oriented computer programming and the principal architect, designer and implementer of five generations of Smalltalk environments. He designed the bytecoded virtual machine that m ...

Bill Atkinson William Dana Atkinson (March 17, 1951 – June 5, 2025) was an American computer engineer, computer programmer, and photographer. Atkinson worked at Apple Computer from 1978 to 1990. Some of Atkinson's noteworthy contributions to the field of ...

and others provided Sassenrath with a wealth of resources and knowledge that helped shape his views of computing languages and systems.

Sassenrath Research

In 1988, Sassenrath left Silicon Valley for the mountains of Ukiah valley, 2 hours north of San Francisco. From there he founded multimedia technology companies such as Pantaray, American Multimedia, and VideoStream. He also implemented the

Logo programming language Logo is an educational programming language, designed in 1967 by Wally Feurzeig, Seymour Papert, and Cynthia Solomon. The name was coined by Feurzeig while he was at Bolt, Beranek and Newman, and derives from the Greek ''logos'', meaning 'word' ...

for the

, managed the software OS development for

CDTV The CDTV (from Commodore Dynamic Total Vision, later treated as a backronym for Compact Disc Television) is a home multimedia entertainment and video game console – convertible into a full-fledged personal computer by the addition of optiona ...

, one of the first

CD-ROM A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains computer data storage, data computers can read, but not write or erase. Some CDs, called enhanced CDs, hold b ...

set-top box A set-top box (STB), also known as a cable converter box, cable box, receiver, or simply box, and historically television decoder or a converter, is an information appliance device that generally contains a Tuner (radio)#Television, TV tuner inpu ...

es, and wrote the OS for Viscorp Ed, one of the first Internet TV set-top boxes.

REBOL Technologies

In 1996, after watching the growth and development of programming languages like

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

, and

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (prog ...

, Sassenrath decided to publish his own ideas within the world of computer languages. The result was REBOL, the ''relative expression-based object language''. REBOL is intended to be lightweight, and specifically to support efficient

. Sassenrath describes REBOL as a balance between the concepts of

context In semiotics, linguistics, sociology and anthropology, context refers to those objects or entities which surround a ''focal event'', in these disciplines typically a communicative event, of some kind. Context is "a frame that surrounds the event ...

and

symbol A symbol is a mark, Sign (semiotics), sign, or word that indicates, signifies, or is understood as representing an idea, physical object, object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen by cr ...

ism, allowing users to create new relationships between symbols and their meanings. By doing so, he attempts to merge the concepts of

code In communications and information processing, code is a system of rules to convert information—such as a letter, word, sound, image, or gesture—into another form, sometimes shortened or secret, for communication through a communicati ...

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

, and

metadata Metadata (or metainformation) is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including: * Descriptive ...

. Sassenrath considers REBOL experimental because it provides greater control over context than most other programming languages. Words can be used to form different grammars in different contexts (called ''dialecting''). Sassenrath claims REBOL is the ultimate endpoint for the evolution of

markup language A markup language is a Encoding, text-encoding system which specifies the structure and formatting of a document and potentially the relationships among its parts. Markup can control the display of a document or enrich its content to facilitate au ...

methodologies, such as

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...

. In 1998, Sassenrath founded REBOL Technologies, a company he still runs. The company has released several versions of REBOL and produced additional products such as REBOL/View, REBOL/Command, REBOL/SDK, and REBOL/IOS. Sassenrath implemented REBOL V3.0 and released it to

GitHub GitHub () is a Proprietary software, proprietary developer platform that allows developers to create, store, manage, and share their code. It uses Git to provide distributed version control and GitHub itself provides access control, bug trackin ...

on December 12, 2012: https://github.com/rebol/r3.

Roku

Since 2010, Sassenrath had worked at Roku, Inc. in product development. He retired in November 2023.

Personal

Sassenrath lives in Ukiah,

, where he grows grapes and makes wine, and is interested in

, video production,

quantum electrodynamics In particle physics, quantum electrodynamics (QED) is the Theory of relativity, relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quant ...

, and boating. He volunteers with the Television Improvement Association, a community organization that brings free, over-the-air television broadcasts into the Ukiah area.

Other references

* ''Amiga ROM Kernel Reference Manual: Exec''; Carl Sassenrath; Commodore; 1986 * ''Guru's Guide to the Commodore Amiga''; Carl Sassenrath; 1989 * ''The Object Oriented Amiga Exec''; Tim Holloway; Byte Magazine; 1991 * ''REBOL Bots''; Web Techniques; 9/1999 * ''Inside the REBOL Scripting Language''; Dr. Dobb's Journal; 6/2000 * ''REBOL for Dummies''; Ralph Roberts; Hungry Minds; 2000 * ''REBOL Programming''; Olivier Auverlot; Éditions Eyrolles; 2001 * ''Computing Encyclopedia, Vol 5: People''; Smart Computing; 2002 * ''The REBOL IOS Distributed Filesystem''; Dr. Dobb's Journal; 9/2002 * ''The REBOL/Core Users Guide''; Carl Sassenrath; 2000–2005

Notes

External links

Personal home page

at REBOL.com
Carl's Blog
at REBOL.com
TIA - The TV Improvement Association

Interview
Obligement, May 2007 *

MakeDoc {{More citations needed, date=April 2023 MakeDoc is a lightweight markup language created in 2000 by Carl Sassenrath for creating documentation and web pages using simple text notations. The language is used extensively in the REBOL community for ...

- Lightweight document markup * Jeudy, Sébastien
Interview with Carl Sassenrath
Obligement, May 2007, accessed October 10, 2013 {{DEFAULTSORT:Sassenrath, Carl 1957 births Living people American computer scientists Programming language designers Amiga people Kernel programmers People from Ukiah, California University of California, Davis alumni Engineers from California Amateur radio people