Jochen Liedtke (26 May 1953 – 10 June 2001) was a German

computer scientist A computer scientist is a person who is trained in the academic study of computer science. Computer scientists typically work on the theoretical side of computation, as opposed to the hardware side on which computer engineers mainly focus (al ...

, noted for his work on

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, ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s, especially in creating the

L4 microkernel family L4 is a family of second-generation microkernels, used to implement a variety of types of operating systems (OS), though mostly for Unix-like, ''Portable Operating System Interface'' (POSIX) compliant types. L4, like its predecessor microkernel ...

Vita

Education

In the mid-1970s Liedtke studied for a diploma degree in mathematics at the

Bielefeld University Bielefeld University (german: Universität Bielefeld) is a university in Bielefeld, Germany. Founded in 1969, it is one of the country's newer universities, and considers itself a "reform" university, following a different style of organization ...

. His thesis project was to build a

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

for the programming language ELAN, which had been launched for teaching programming in German schools. The compiler was written in ELAN.

Post grad

After his graduation in 1977, he remained at Bielefeld and worked on an Elan environment for the

Zilog Z80 The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples wer ...

microprocessor. This required a

runtime system In computer programming, a runtime system or runtime environment is a sub-system that exists both in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile t ...

(environment), which he named

Eumel EUMEL (pronounced ''oimel'' for Extendable Multi User Microprocessor ELAN System and also known as L2 for Liedtke 2) is an operating system (OS) which began as a runtime system (environment) for the programming language ELAN. It was created in 1 ...

("Extendable Multiuser Microprocessor ELAN-System", but also a colloquial north-German term for
likeable fool
. Eumel grew into a complete multi-tasking, multi-user

supporting

orthogonal persistence In computer science, persistence refers to the characteristic of state of a system that outlives (persists more than) the process that created it. This is achieved in practice by storing the state as data in computer data storage. Programs have ...

, which started shipping (^{by whom? to whom?}) in 1980 and was later ported to

Zilog Z8000 The Z8000 ("''zee-'' or ''zed-eight-thousand''") is a 16-bit microprocessor introduced by Zilog in early 1979. The architecture was designed by Bernard Peuto while the logic and physical implementation was done by Masatoshi Shima, assisted by a ...

Motorola 68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector ...

and

Intel 8086 The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...

processors. As these processors lacked memory protection, Eumel implemented a

virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...

which added the features missing from the hardware. More than 2000 Eumel systems shipped, mostly to schools, and some to legal practices as a

text processing In computing, the term text processing refers to the theory and practice of automating the creation or manipulation of electronic text. ''Text'' usually refers to all the alphanumeric characters specified on the keyboard of the person engaging t ...

platform. In 1984, he joined the ' (GMD), the German National Research Center for Computer Science, which is now a part of the

Fraunhofer Society The Fraunhofer Society (german: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V., lit=Fraunhofer Society for the Advancement of Applied Research) is a German research organization with 76institutes spread throughout Germany ...

. There, he continued his work on Eumel. In 1987, when microprocessors supporting

virtual memory In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very l ...

became widely available in the form of the

Intel 80386 The Intel 386, originally released as 80386 and later renamed i386, is a 32-bit microprocessor introduced in 1985. The first versions had 275,000 transistorsL3 ("Liedtke's 3rd system", after Eumel and the

ALGOL 60 ALGOL 60 (short for ''Algorithmic Language 1960'') is a member of the ALGOL family of computer programming languages. It followed on from ALGOL 58 which had introduced code blocks and the begin and end pairs for delimiting them, representing a k ...

interpreter he had written in high school). L3 was designed to achieve better performance by using the latest hardware features, and was implemented from scratch. It was mostly backward-compatible with Eumel, thus benefiting from the existing Eumel ecosystem. L3 started to ship in 1989, with total deployment of at least 500. Both Eumel and L3 were

systems, a popular design in the 1980s. However, by the early 1990s, microkernels had received a bad reputation, as systems built on top were performing poorly, culminating in the billion-dollar failure of the IBM Workplace OS. The reason was claimed to be inherent in the operating-system structure imposed by microkernels. Liedtke, however, observed that the message-passing operation (IPC), which is fundamentally important for microkernel performance, was slow in all existing microkernels, including his own L3 system. His conclusion was that radical redesign was needed. He did this by re-implementing L3 from scratch, dramatically simplifying the kernel, resulting in an order-of-magnitude decrease in IPC cost. The resulting kernel was later renamed "L4". Conceptually, the main novelty of L4 was its complete reliance on external pagers (

page fault In computing, a page fault (sometimes called PF or hard fault) is an exception that the memory management unit (MMU) raises when a process accesses a memory page without proper preparations. Accessing the page requires a mapping to be added to t ...

handlers), and the recursive construction of address spaces. This led to a complete family of microkernels, with many independent implementations of the same principles. Liedtke also worked on

computer architecture In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, t ...

, inventing guarded

page table A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are used by the program executed by the accessing process, ...

s as a means to implement a sparsely-mapped

64-bit In computer architecture, 64-bit Integer (computer science), integers, memory addresses, or other Data (computing), data units are those that are 64 bits wide. Also, 64-bit central processing unit, CPUs and arithmetic logic unit, ALUs are those ...

address space. In 1996, Liedtke completed a PhD on guarded page tables at the

Technical University of Berlin The Technical University of Berlin (official name both in English and german: link=no, Technische Universität Berlin, also known as TU Berlin and Berlin Institute of Technology) is a public research university located in Berlin, Germany. It was ...

. In the same year he joined the

Thomas J. Watson Research Center The Thomas J. Watson Research Center is the headquarters for IBM Research. The center comprises three sites, with its main laboratory in Yorktown Heights, New York, U.S., 38 miles (61 km) north of New York City, Albany, New York and wit ...

, where he continued to work on L4, referred to as “Lava Nucleus” (LN) to avoid negative connotations with previously unsuccessful microkernels, such as the one used in

Workplace OS Workplace OS is IBM's ultimate operating system prototype of the 1990s. It is the product of an exploratory research program in 1991 which yielded a design called the Grand Unifying Theory of Systems (GUTS), proposing to unify the world's system ...

. The main project during his IBM time was the Saw Mill project, which attempted to turn

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

into an L4-based multi-server OS. In April 1999, he took up the System Architecture Chair at the

University of Karlsruhe The Karlsruhe Institute of Technology (KIT; german: Karlsruher Institut für Technologie) is a public research university in Karlsruhe, Germany. The institute is a national research center of the Helmholtz Association. KIT was created in 2009 w ...

. There, he continued to collaborate with IBM on Saw Mill, but at the same time worked on a new generation of L4 (version 4). Several experimental kernels were developed during that time, including Hazelnut, the first L4 kernel that was ported (in contrast to re-implemented) to a different architecture (from

x86 x86 (also known as 80x86 or the 8086 family) is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the Intel 8086 microprocessor and its 8088 variant. The 8086 was introd ...

ARM In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...

). Work on the new version was completed after his death by Liedtke's students Volkmar Uhlig, Uwe Dannowski, and Espen Skoglund. It was released under the name ''Pistachio'' in 2002. On Sunday June 10, 2001, he died unexpectedly at

Frankfurt Airport Frankfurt Airport (; german: link=no, Flughafen Frankfurt Main , also known as ''Rhein-Main-Flughafen'') is a major international airport located in Frankfurt, the fifth-largest city of Germany and one of the world's leading financial centres ...

while returning from SOSP'01 program committee meeting in

Chateau Lake Louise The Fairmont Chateau Lake Louise is a Fairmont hotel on the eastern shore of Lake Louise, near Banff, Alberta. The original hotel was gradually developed at the turn of the 20th century by the Canadian Pacific Railway and was thus "kin" to its ...

, having being ill earlier in the year and undergone two surgeries (the conference proceedings were dedicated to his memory). He is survived by his wife Adelheid.

References

External links

In Memoriam Jochen Liedtke (1953 - 2001)

List of Liedtke's publications
related to microkernels {{DEFAULTSORT:Liedtke, Jochen 1953 births 2001 deaths German computer scientists Computer systems researchers Kernel programmers