Aleph kernel
Encyclopedia
Aleph was an operating system
kernel developed at the University of Rochester
as part of their RIG project in 1975. Aleph used inter-process communication
s to move data between programs and the kernel, so applications could transparently access resources on any machine on the local area network (which at the time was a 3-Mbit/s experimental Xerox
Ethernet
). The project eventually petered out after several years due to rapid changes in the computer hardware market, but the ideas led to the creation of Accent
at Carnegie Mellon University
, leading in turn to Mach.
Applications written for the RIG system communicated via ports. Ports were essentially message queues that were maintained by the Aleph kernel, identified by a machine unique (as opposed to globally unique) ID consisting of a process id, port id pair. Processes were automatically assigned a process number, or pid, on startup, and could then ask the kernel to open ports. Processes could open several ports and then "read" them, automatically blocking and allowing other programs to run until data arrived. Processes could also "shadow" another, receiving a copy of every message sent to the one it was shadowing. Similarly, programs could "interpose" on another, receiving messages and essentially cutting the original message out of the conversation.
RIG was implemented on a number of Data General Eclipse
minicomputer
s. This presented a major performance problem because the system could copy data only 2kB at a time. Another problem, realized only in retrospect, was that the use of global ID's allowed malicious software to "guess" at ports and thereby gain access to resources they should not have had.
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
kernel developed at the University of Rochester
University of Rochester
The University of Rochester is a private, nonsectarian, research university in Rochester, New York, United States. The university grants undergraduate and graduate degrees, including doctoral and professional degrees. The university has six schools and various interdisciplinary programs.The...
as part of their RIG project in 1975. Aleph used inter-process communication
Inter-process communication
In computing, Inter-process communication is a set of methods for the exchange of data among multiple threads in one or more processes. Processes may be running on one or more computers connected by a network. IPC methods are divided into methods for message passing, synchronization, shared...
s to move data between programs and the kernel, so applications could transparently access resources on any machine on the local area network (which at the time was a 3-Mbit/s experimental Xerox
Xerox PARC
PARC , formerly Xerox PARC, is a research and co-development company in Palo Alto, California, with a distinguished reputation for its contributions to information technology and hardware systems....
Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
). The project eventually petered out after several years due to rapid changes in the computer hardware market, but the ideas led to the creation of Accent
Accent kernel
Accent was an operating system kernel developed at Carnegie Mellon University . Accent was developed as a follow-on to the Aleph kernel developed at the University of Rochester, fixing several of its problems and re-targeting its hardware support for networks of workstation machines instead of...
at Carnegie Mellon University
Carnegie Mellon University
Carnegie Mellon University is a private research university in Pittsburgh, Pennsylvania, United States....
, leading in turn to Mach.
Applications written for the RIG system communicated via ports. Ports were essentially message queues that were maintained by the Aleph kernel, identified by a machine unique (as opposed to globally unique) ID consisting of a process id, port id pair. Processes were automatically assigned a process number, or pid, on startup, and could then ask the kernel to open ports. Processes could open several ports and then "read" them, automatically blocking and allowing other programs to run until data arrived. Processes could also "shadow" another, receiving a copy of every message sent to the one it was shadowing. Similarly, programs could "interpose" on another, receiving messages and essentially cutting the original message out of the conversation.
RIG was implemented on a number of Data General Eclipse
Data General Eclipse
The Data General Eclipse line of computers by Data General were 16-bit minicomputers released in early 1974 and sold until 1988. The Eclipse was based on many of the same concepts as the Data General Nova, but included support for virtual memory and multitasking more suitable to the small office...
minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
s. This presented a major performance problem because the system could copy data only 2kB at a time. Another problem, realized only in retrospect, was that the use of global ID's allowed malicious software to "guess" at ports and thereby gain access to resources they should not have had.