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Memory bandwidth is the rate at which data can be read from or stored into a semiconductor memory by a processor. Memory bandwidth is usually expressed in units of bytes/second , though this can vary for systems with natural data sizes that are not a multiple of the commonly used 8-bit bytes.
The gap between processor speed and main memory speed has grown exponentially. Until 2001–05, CPU speed, as measured by clock frequency, grew annually by 55%, whereas memory speed only grew by 7%. [1] This problem is known as the memory wall. The motivation for a cache and its hierarchy is to bridge this speed gap and overcome the memory wall.
Memory operations per second or MOPS is a metric for an expression of the performance capacity of semiconductor memory. It can also be used to determine the efficiency of RAM in the Windows operating environment. [1] [2] MOPS can be affected by multiple applications being open at once without adequate job scheduling. [3]
That said, the price of high-capacity drives has fallen rapidly, and this is indeed an effect of density. The highest capacity drives use more platters, essentially individual hard drives within the case. As the density increases, the number of platters can be reduced, leading to lower costs. Hard drives are often measured in terms of cost per bit.
Computer memory caches usually operate on blocks of memory that consist of several consecutive words. These units are customarily called cache blocks, or, in CPU caches, cache lines. Virtual memory systems partition the computer's main storage into even larger units, traditionally called pages.
The memory storage capacity for M number of address lines is given by 2 M, which is usually in power of two: 2, 4, 8, 16, 32, 64, 128, 256 and 512 and measured in kilobits, megabits, gigabits or terabits, etc. As of 2014 the largest semiconductor memory chips hold a few gigabits of data, but higher capacity memory is constantly being developed.
Computer memory used in most contemporary computer systems is built mainly out of DRAM cells; since the layout is much smaller than SRAM, it can be more densely packed yielding cheaper memory with greater capacity. Since the DRAM memory cell stores its value as the charge of a capacitor, and there are current leakage issues, its value must be ...
The channel capacity is defined as ... the channel has memory. Consider for instance the simple case on an autoregressive model noise process = ...