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In computer science, partitioned global address space (PGAS) is a parallel programming model paradigm. PGAS is typified by communication operations involving a global memory address space abstraction that is logically partitioned, where a portion is local to each process, thread, or processing element .
Each segment was placed at a specific location in memory by the software being executed and all instructions that operated on the data within those segments were performed relative to the start of that segment. This allowed a 16-bit address register, which would normally be able to access 64 KB of memory space, to access 1 MB of memory space.
The logical address space (that is, the address space available at any moment without changing the memory mapping table) remains limited to 16 bits. Some models, beginning with the PDP-11/45, can be set to use 32K words (64 KB) as the "instruction space" for program code and a separate 32K words of "data space".
Data locality is a typical memory reference feature of regular programs (though many irregular memory access patterns exist). It makes the hierarchical memory layout profitable. In computers, memory is divided into a hierarchy in order to speed up data accesses. The lower levels of the memory hierarchy tend to be slower, but larger.
Java theory and practice: Fixing the Java Memory Model, part 1 - An article describing problems with the original Java memory model. Java theory and practice: Fixing the Java Memory Model, part 2 - Explains the changes JSR 133 made to the Java memory model. Java Memory Model Pragmatics (transcript) The Java Memory Model links; Java internal ...
A pointer a pointing to the memory address associated with a variable b, i.e., a contains the memory address 1008 of the variable b. In this diagram, the computing architecture uses the same address space and data primitive for both pointers and non-pointers; this need not be the case.
Address spaces are created by combining enough uniquely identified qualifiers to make an address unambiguous within the address space. For a person's physical address, the address space would be a combination of locations, such as a neighborhood, town, city, or country. Some elements of a data address space may be the same, but if any element ...
A memory address a is said to be n-byte aligned when a is a multiple of n (where n is a power of 2). In this context, a byte is the smallest unit of memory access, i.e. each memory address specifies a different byte. An n-byte aligned address would have a minimum of log 2 (n) least-significant zeros when expressed in binary.