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In computing, sequential access memory (SAM) is a class of data storage devices that read stored data in a sequence. This is in contrast to random access memory (RAM) where data can be accessed in any order. Sequential access devices are usually a form of magnetic storage or optical storage. [1] [2]
Sequential access compared to random access. Sequential access is a term describing a group of elements (such as data in a memory array or a disk file or on magnetic-tape data storage) being accessed in a predetermined, ordered sequence. It is the opposite of random access, the ability to access an arbitrary element of a sequence as easily and ...
In computing, a memory access pattern or IO access pattern is the pattern with which a system or program reads and writes memory on secondary storage.These patterns differ in the level of locality of reference and drastically affect cache performance, [1] and also have implications for the approach to parallelism [2] [3] and distribution of workload in shared memory systems. [4]
[1] [4] Conversely, the memory order is called weak or relaxed when one thread cannot predict the order of operations arising from another thread. [1] [4] Many naïvely written parallel algorithms fail when compiled or executed with a weak memory order. [5] [6] The problem is most often solved by inserting memory barrier instructions into the ...
A model, called Concurrent-AMAT (C-AMAT), is introduced for more accurate analysis of current memory systems. More information on C-AMAT can be found in the external links section. AMAT's three parameters hit time (or hit latency), miss rate, and miss penalty provide a quick analysis of memory systems.
The average memory reference time is [1] = + + where = miss ratio = 1 - (hit ratio) = time to make main-memory access when there is a miss (or, with a multi-level cache, average memory reference time for the next-lower cache)
In IBM mainframe operating systems, Basic sequential access method (BSAM) [1] is an access method to read and write datasets sequentially. BSAM is available on OS/360, OS/VS2, MVS, z/OS, and related operating systems. BSAM is used for devices that are naturally sequential, such as punched card readers, punches, line printers, and magnetic tape.
Sequential consistency can be achieved simply by hardware implementation, while release consistency is also based on an observation that most of the parallel programs are properly synchronized. In programming level, synchronization is applied to clearly schedule a certain memory access in one thread to occur after another.