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Speed of operation

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neptune

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hello,

I am studying memory hierarchy right now, and i came to the conclusion that Computers speed of operation depends on slowest memory working inside it.
That means it doesnt matter if we continue to increase the speed of CPU from Mhz to Ghz, majority of programmes running on computer will be slow , with high latency and slow response time.

So, the real problem is increasing the speed of memory read and write. did i get things correctly ?

secondly, if one memory has high read speed but slow write speed or vice versa , what will be the consequences of that on computer systems.
 
Basically it is true. Caches are a way to increase the dataflow, as well as multithreading, which when a cache fault occurs allows the procesor to switch context to other thread which has data ready, so the first process waits until the data gets loaded into the cache.
This provides better utilisation of cpu power, but for single threaded application´s performance this has no effect. The only solution is to either pre-cache data - this is usually not possible under OS for L1..3 caches, so such memory intensive application would have to be standalone and carefully use the available caches to get the best performace. For disk I/O, applications should pre-cache into dram, which is ~1000 faster than hard disks, and work with data in memory.

Another way for getting faster dram access is slicing the ram into multiple physical banks so you get faster throughput overall.

Second question depends on which memory you´re talking about. Hard disks have comaparatively large caches than drams, so slow write speeds can be somewhat masked by the cache. Slow read speed will definitely slow the programm, especially for random seeks.
For dram, write speeds are similar to read speeds. If one was slower and you had symmetrical r/w demands, the lowest would be the bottleneck, since the write cache in a processor is pretty small.
 
i dont know much about this but surely dosnt matter how good the hardware is or speed of that but depends more on how the software is done?? i know in pics that there is many ways to say flash a led but some ways realy slow down the pic? so surely software is just a big a part of the speed of a computer??
lg
 
That is true, for example an application made in java or .net will be much slower than something written in C, which will be slower than something hand optimized in assembler, the choice of programming language affects the number of steps involved in calculating a single number. Also the choice of programming paradigms and algorithms will affect the result a lot, but this has little to do with the actual CPU - RAM bottle neck, where RAM bus speed is 5-10 times lower than CPU clock, which leads to slow acces times and the need to use bulk transfers of larger amounts of data into cache rather than directly asking the ram for a single byte each time.
 
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Alright then,
I think the majority of programs require lot of Read operation and less of Write operation.
can you give me the chart specifying the speed of all types of memory in exact. Like flash memory , optical memory , etc.
 
can you get that kind of info from datasheets? i doubt anyone just has it laying about ?? it might be an idea to look on wikipedia they seem big on charts try searching for pc memory and see where the links take you not sure what else to sugest its out of my knowledg sorry
lg
 
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but still can there must be some numbers. the image that i prepared was googling fastest available products in market. :)
 
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