Heterogeneous Element Processor
Encyclopedia
The Heterogeneous Element Processor (HEP) was introduced by Denelcor in 1982 as the world's first commercial MIMD
computer. A HEP system, as the name implies, was pieced together from many heterogeneous components -- processors
, data memory modules, and I/O modules. The components were connected via a switched network
.
A single processor in a HEP system (up to sixteen could be connected) was rather unconventional; via a "program status word (PSW) queue," up to fifty processes could be maintained in hardware at once. The eight-stage instruction pipeline
allowed instructions from eight different processes to proceed at once. In fact, only one instruction from a given process was allowed to be present in the pipeline at any point in time. Therefore, the full processor throughput of 10 MIPS could only be achieved when eight or more processes were active; no single process could achieve throughput greater than 1.25 MIPS. This type of multithreading processing classifies the HEP as a barrel processor
.
Processes were classified as either user-level or supervisor-level. User-level processes could create supervisor-level processes, which were used to manage user-level processes and perform I/O. Processes of the same class were required to be grouped into one of seven user tasks and seven supervisor tasks.
Each processor, in addition to the PSW queue and instruction pipeline, contained instruction memory, 2,048 64-bit general purpose registers
and 4,096 constant registers. Constant registers were differentiated by the fact that only supervisor processes could modify their contents. Interestingly, the processors themselves contained no data memory; instead, data memory modules could be separately attached to the switched network.
The HEP implemented a type of mutual exclusion
in which all registers and locations in data memory had associated "empty" and "full" states. Reading from a location set the state to "empty," while writing to it set the state to "full." A programmer could allow processes to halt after trying to read from an empty location or write to a full location, enforcing critical sections.
The switched network between elements resembled, in many ways, a modern computer network. On the network were sets of nodes, each of which had three links. When a packet arrived at a node, it consulted a routing table and attempted to forward the packet closer to its destination. If a node became congested, any incoming packets were passed on without routing. Packets treated in such a manner had their priority level increased; when several packets vied for a single node, a packet with a higher priority level would be routed before ones with lower priority levels.
Although it was known to have poor cost-performance, the HEP received attention due to what were, at the time, several revolutionary features. HEP systems were purchased by Los Alamos
, the Argonne National Laboratory
, the Ballistic Research Laboratory, and
The HEP attracted widespread attention despite its terrible cost performance because of its many interesting hardware features that facilitated programming. The Denelcor HEP was acquired by several institutions, including Los Alamos, Argonne National Laboratory, Ballistic Research Laboratory, and Germany's Messerschmitt. Messerschmitt was the only client to put the HEP into use for "real" applications; the other clients used it for experimenting with parallel algorithms.
MIMD
In computing, MIMD is a technique employed to achieve parallelism. Machines using MIMD have a number of processors that function asynchronously and independently. At any time, different processors may be executing different instructions on different pieces of data...
computer. A HEP system, as the name implies, was pieced together from many heterogeneous components -- processors
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, data memory modules, and I/O modules. The components were connected via a switched network
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
.
A single processor in a HEP system (up to sixteen could be connected) was rather unconventional; via a "program status word (PSW) queue," up to fifty processes could be maintained in hardware at once. The eight-stage instruction pipeline
Instruction pipeline
An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput ....
allowed instructions from eight different processes to proceed at once. In fact, only one instruction from a given process was allowed to be present in the pipeline at any point in time. Therefore, the full processor throughput of 10 MIPS could only be achieved when eight or more processes were active; no single process could achieve throughput greater than 1.25 MIPS. This type of multithreading processing classifies the HEP as a barrel processor
Barrel processor
A barrel processor is a CPU that switches between threads of execution on every cycle. This CPU design technique is also known as "interleaved" or "fine-grained" temporal multithreading...
.
Processes were classified as either user-level or supervisor-level. User-level processes could create supervisor-level processes, which were used to manage user-level processes and perform I/O. Processes of the same class were required to be grouped into one of seven user tasks and seven supervisor tasks.
Each processor, in addition to the PSW queue and instruction pipeline, contained instruction memory, 2,048 64-bit general purpose registers
Processor register
In computer architecture, a processor register is a small amount of storage available as part of a CPU or other digital processor. Such registers are addressed by mechanisms other than main memory and can be accessed more quickly...
and 4,096 constant registers. Constant registers were differentiated by the fact that only supervisor processes could modify their contents. Interestingly, the processors themselves contained no data memory; instead, data memory modules could be separately attached to the switched network.
The HEP implemented a type of mutual exclusion
Mutual exclusion
Mutual exclusion algorithms are used in concurrent programming to avoid the simultaneous use of a common resource, such as a global variable, by pieces of computer code called critical sections. A critical section is a piece of code in which a process or thread accesses a common resource...
in which all registers and locations in data memory had associated "empty" and "full" states. Reading from a location set the state to "empty," while writing to it set the state to "full." A programmer could allow processes to halt after trying to read from an empty location or write to a full location, enforcing critical sections.
The switched network between elements resembled, in many ways, a modern computer network. On the network were sets of nodes, each of which had three links. When a packet arrived at a node, it consulted a routing table and attempted to forward the packet closer to its destination. If a node became congested, any incoming packets were passed on without routing. Packets treated in such a manner had their priority level increased; when several packets vied for a single node, a packet with a higher priority level would be routed before ones with lower priority levels.
Although it was known to have poor cost-performance, the HEP received attention due to what were, at the time, several revolutionary features. HEP systems were purchased by Los Alamos
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
, the Argonne National Laboratory
Argonne National Laboratory
Argonne National Laboratory is the first science and engineering research national laboratory in the United States, receiving this designation on July 1, 1946. It is the largest national laboratory by size and scope in the Midwest...
, the Ballistic Research Laboratory, and
The HEP attracted widespread attention despite its terrible cost performance because of its many interesting hardware features that facilitated programming. The Denelcor HEP was acquired by several institutions, including Los Alamos, Argonne National Laboratory, Ballistic Research Laboratory, and Germany's Messerschmitt. Messerschmitt was the only client to put the HEP into use for "real" applications; the other clients used it for experimenting with parallel algorithms.