The C.mmp was an early multiple instruction, multiple data (MIMD) multiprocessor system developed at Carnegie Mellon University (CMU) by William Wulf (1971). The notation C.mmp came from the PMS notation of Gordon Bell and Allen Newell, [1] where a central processing unit (CPU) was designated as C, a variant was noted by the dot notation, and mmp stood for Multi-Mini-Processor. As of 2020 [update] , the machine is on display at CMU, in Wean Hall, on the ninth floor.
Sixteen Digital Equipment Corporation PDP-11 minicomputers were used as the processing elements, named Compute Modules (CMs) in the system. Each CM had a local memory of 8K and a local set of peripheral devices. One of the challenges was that a device was only available through its unique connected processor, so the input/output (I/O) system (designed by Roy Levien) hid the connectivity of the devices and routed the requests to the hosting processor. If a processor went down, the devices connected to its Unibus became unavailable, which became a problem in overall system reliability. Processor 0 (the boot processor) had the disk drives attached.
Each of the Compute Modules shared these communication pathways:
Since the PDP-11 had a logical address space of 16-bits, another address translation unit was added to expand the address space to 25 bits for the shared memory space. The Unibus architecture provided 18 bits of physical address, and the two high-order bits were used to select one of four relocation registers which selected a bank of memory. Properly managing these registers was one of the challenges of programming the operating system (OS) kernel.
The original C.mmp design used magnetic-core memory, but during its lifetime, higher performance dynamic random-access memory (RAM) became available and the system was upgraded.
The original processors were PDP-11/20 processors, but in the final system, only five of these were used; the remaining 11 were PDP-11/40 processors, which were modified by having extra writeable microcode space.[ citation needed ] All modifications to these machines were designed and built at CMU.
Most of the 11/20 modifications were custom changes to the wire-wrapped backplane, but because the PDP-11/40 was implemented in microcode, a separate proc-mod board was designed that intercepted certain instructions and implemented the protected operating system requirements. For example, it was necessary, for operating system integrity, that the stack pointer register never be odd. On the 11/20, this was done by clipping the lead to the low-order bit of the stack register. On the 11/40, any access to the stack was intercepted by the proc-mod board and generated an illegal data access trap if the low-order bit was 1.
The operating system (OS) was named Hydra. It was capability-based, object-oriented, multi-user, and a microkernel. System resources were represented as objects and protected through capabilities.
The OS and most application software was written in the programming language BLISS-11, which required cross-compiling on a PDP-10. The OS used very little assembly language.
Among the programming languages available on the system was an ALGOL 68 variant which included extensions supporting parallel computing, to make good use of the C.mmp. The ALGOL compiler ran native on Hydra OS.
Because overall system reliability depended on having all 16 CPUs running, there were serious problems with overall hardware reliability. If the mean time between failures (MTBF) of one processor was 24 hours, then the overall system reliability was 16/24 hours, or about 40 minutes. Overall, the system usually ran for between two and six hours. [2] Many of these failures were due to timing glitches in the many custom circuits added to the processors. Great effort was expended to improve hardware reliability, and when a processor was noticeably failing, it was partitioned out, and would run diagnostics for several hours. When it had passed a first set of diagnostics, it was partitioned back in as an I/O processor and would not run application code (but its peripheral devices were now available); it continued to run diagnostics. If it passed these after several more hours, it was reinstated as a full member of the processor set. Similarly, if a block of memory (one page) was detected as faulty, it was removed from the pool of available pages, and until otherwise notified, the OS would ignore this page. Thus, the OS became an early example of a fault-tolerant system, able to deal with hardware problems which arose, inevitably.
A control store is the part of a CPU's control unit that stores the CPU's microprogram. It is usually accessed by a microsequencer. A control store implementation whose contents are unalterable is known as a Read Only Memory (ROM) or Read Only Storage (ROS); one whose contents are alterable is known as a Writable Control Store (WCS).
In computer architecture, a bus is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components and software, including communication protocols.
In processor design, microcode serves as an intermediary layer situated between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. It consists of a set of hardware-level instructions that implement higher-level machine code instructions or control internal finite-state machine sequencing in many digital processing components. While microcode is utilized in general-purpose CPUs in contemporary desktops, it also functions as a fallback path for scenarios that the faster hardwired control unit is unable to manage.
Mach is a kernel developed at Carnegie Mellon University by Richard Rashid and Avie Tevanian to support operating system research, primarily distributed and parallel computing. Mach is often considered one of the earliest examples of a microkernel. However, not all versions of Mach are microkernels. Mach's derivatives are the basis of the operating system kernel in GNU Hurd and of Apple's XNU kernel used in macOS, iOS, iPadOS, tvOS, and watchOS.
Digital Equipment Corporation (DEC)'s PDP-10, later marketed as the DECsystem-10, is a mainframe computer family manufactured beginning in 1966 and discontinued in 1983. 1970s models and beyond were marketed under the DECsystem-10 name, especially as the TOPS-10 operating system became widely used.
The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units being sold over the model's lifetime. Its basic design follows the pioneering LINC but has a smaller instruction set, which is an expanded version of the PDP-5 instruction set. Similar machines from DEC are the PDP-12 which is a modernized version of the PDP-8 and LINC concepts, and the PDP-14 industrial controller system.
The PDP–11 is a series of 16-bit minicomputers sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of all models were sold, making it one of DEC's most successful product lines. The PDP-11 is considered by some experts to be the most popular minicomputer.
RT-11 is a discontinued small, low-end, single-user real-time operating system for the full line of Digital Equipment Corporation PDP-11 16-bit computers. RT-11 was first implemented in 1970. It was widely used for real-time computing systems, process control, and data acquisition across all PDP-11s. It was also used for low-cost general-use computing.
William Allan Wulf was an American computer scientist notable for his work in programming languages and compilers.
BLISS is a system programming language developed at Carnegie Mellon University (CMU) by W. A. Wulf, D. B. Russell, and A. N. Habermann around 1970. It was perhaps the best known system language until C debuted a few years later. Since then, C became popular and common, and BLISS faded into obscurity. When C was in its infancy, a few projects within Bell Labs debated the merits of BLISS vs. C.
DECtape, originally called Microtape, is a magnetic tape data storage medium used with many Digital Equipment Corporation computers, including the PDP-6, PDP-8, LINC-8, PDP-9, PDP-10, PDP-11, PDP-12, and the PDP-15. On DEC's 32-bit systems, VAX/VMS support for it was implemented but did not become an official part of the product lineup.
The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon Bell and student Harold McFarland while at Carnegie Mellon University.
The Q-bus, also known as the LSI-11 Bus, is one of several bus technologies used with PDP and MicroVAX computer systems previously manufactured by the Digital Equipment Corporation of Maynard, Massachusetts.
The PDP-5 was Digital Equipment Corporation's first 12-bit computer, introduced in 1963.
The VAX-11 is a discontinued family of 32-bit superminicomputers, running the Virtual Address eXtension (VAX) instruction set architecture (ISA), developed and manufactured by Digital Equipment Corporation (DEC). Development began in 1976. In addition to being powerful machines in their own right, they also offer the additional ability to run user mode PDP-11 code, offering an upward compatible path for existing customers.
Digital Equipment Corporation's RK05 is a disk drive whose removable disk pack can hold about 2.5 megabytes of data. Introduced 1972, it is similar to IBM's 1964-introduced 2310, and uses a disk pack similar to IBM's 2315 disk pack, although the latter only held 1 megabyte. An RK04 drive, which has half the capacity of an RK05, was also offered.
Hydra is an early, discontinued, capability-based, object-oriented microkernel designed to support a wide range of possible operating systems to run on it. Hydra was created as part of the C.mmp project at Carnegie-Mellon University in 1971.
The VAX 8000 is a discontinued family of superminicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA).
The PDP-11 architecture is a 16-bit CISC instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC). It is implemented by central processing units (CPUs) and microprocessors used in PDP-11 minicomputers. It was in wide use during the 1970s, but was eventually overshadowed by the more powerful VAX architecture in the 1980s.
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