Cambridge CAP computer on:
[Wikipedia]
[Google]
[Amazon]
The Cambridge CAP computer was the first successful experimental computer that demonstrated the use of security capabilities, both in hardware and software.Levy, p.96 It was developed at the
The 32-bit processor featured microprogramming control, two 256-entry caches, a 32-entry write buffer and the capability unit itself, which had 64 registers for holding evaluated capabilities.
The Cambridge CAP computer was the first successful experimental computer that demonstrated the use of security capabilities, both in hardware and software.Levy, p.96 It was developed at the University of Cambridge Computer Laboratory
The Department of Computer Science and Technology, formerly the Computer Laboratory, is the computer science department of the University of Cambridge. it employed 35 academic staff, 25 support staff, 35 affiliated research staff, and about 15 ...
in the 1970s. Unlike most research machines of the time, it was also a useful service machine.
The sign currently on the front of the machine reads:
The CAP project on memory protection ran from 1970 to 1977. It was based on capabilities implemented in hardware, under M. Wilkes and R. Needham with D. Wheeler responsible for the implementation. R. Needham was awarded a BCS Technical Award in 1978 for the ''CAP (Capability Protection) Project''.
Design
The CAP was designed such that any access to a memory segment or hardware required that the current process held the necessary capabilities.
The 32-bit processor featured microprogramming control, two 256-entry caches, a 32-entry write buffer and the capability unit itself, which had 64 registers for holding evaluated capabilities. Floating point
In computing, floating-point arithmetic (FP) is arithmetic that represents real numbers approximately, using an integer with a fixed precision, called the significand, scaled by an integer exponent of a fixed base. For example, 12.345 can be ...
operations were available using a single 72-bit accumulator. The instruction set featured over 200 instructions, including basic ALU and memory operations, to capability- and process-control instructions.
Instead of the programmer-visible registers used in Chicago and Plessey System 250 Plessey System 250, also known as PP250, was the first operational computer to implement capability-based addressing, to check and balance the computation as a pure Church–Turing machine. Plessey built the systems for a British Army message rout ...
designs, the CAP would load internal registers silently when a program defined a capability. The memory was divided into segments of up to 64K 32-bit words. Each segment could contain data or capabilities, but not both. Hardware was accessed via an associated minicomputer.
All procedures constituting the operating system were written in ALGOL 68C
ALGOL 68C is an imperative computer programming language, a dialect of ALGOL 68, that was developed by Stephen R. Bourne and Michael Guy to program the Cambridge Algebra System (CAMAL). The initial compiler was written in the Princeton Syntax ...
, although a number of other closely associated protected procedures - such as a paginator - are written in BCPL
BCPL ("Basic Combined Programming Language") is a procedural, imperative, and structured programming language. Originally intended for writing compilers for other languages, BCPL is no longer in common use. However, its influence is still ...
.
Operation
The CAP first became operational in 1976. A fully functional computer, it featured a completeoperating 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 ...
, file system
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
, 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 ...
s, and so on. The OS used a process
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic.
Things called a process include:
Business and management
*Business process, activities that produce a specific se ...
tree structure, with an initial process called the "Master coordinator". This removed the need for separate modes of operation, as each process could directly access the resources of its children. In practice, only two levels were ever used during the CAP's operation.
In 1981 the MACRO SPITBOL version of the SNOBOL4 programming language was implemented on the CAP by Nicholas J. L. Brown.Brown, Nicholas J. L. (1981, April). ''CAP SPITBOL Manual and User's Guide''. Unpublished undergraduate dissertation. University of Cambridge Computer Laboratory.
See also
*Plessey System 250 Plessey System 250, also known as PP250, was the first operational computer to implement capability-based addressing, to check and balance the computation as a pure Church–Turing machine. Plessey built the systems for a British Army message rout ...
*IBM System/38
The System/38 is a discontinued minicomputer and midrange computer manufactured and sold by
IBM. The system was announced in 1978. The System/38 has 48-bit addressing, which was unique for the time, and a novel integrated database system. It w ...
*C.mmp
The C.mmp was an early ''multiple instruction, multiple data'' (Multiple instruction, multiple data, MIMD) Multiprocessing, multiprocessor system developed at Carnegie Mellon University (CMU) by William Wulf (1971). The notation ''C.mmp'' came fro ...
* RSRE Flex
Notes
References
* * {{DEFAULTSORT:Cap Computer Computers designed in the United Kingdom Capability systems One-of-a-kind computers University of Cambridge Computer Laboratory