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Memory latency is the time (the latency) between initiating a request for a byte or word in memory until it is retrieved by a processor. If the data are not in the processor's cache , it takes longer to obtain them, as the processor will have to communicate with the external memory cells.
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. Hit latency (H) is the time to hit in the ...
It is for this reason that DDR3-2666 CL9 has a smaller absolute CAS latency than DDR3-2000 CL7 memory. Both for DDR3 and DDR4, the four timings described earlier are not the only relevant timings and give a very short overview of the performance of memory. The full memory timings of a memory module are stored inside of a module's SPD chip.
The CAS latency is the delay between the time at which the column address and the column address strobe signal are presented to the memory module and the time at which the corresponding data is made available by the memory module. The desired row must already be active; if it is not, additional time is required.
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.
Access time is the time delay or latency between a request to an electronic system, and the access being initiated or the requested data returned.. In computer and software systems, it is the time interval between the point where an instruction control unit initiates a call to retrieve data or a request to store data, and the point at which delivery of the data is completed or the storage is ...
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.
In computing, serial presence detect (SPD) is a standardized way to automatically access information about a memory module.Earlier 72-pin SIMMs included five pins that provided five bits of parallel presence detect (PPD) data, but the 168-pin DIMM standard changed to a serial presence detect to encode more information.