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Given the importance, in the area of high performance computing, of the performance of a computer’s memory subsystem, many techniques have been used to improve the performance of the memory systems of computers. The two attributes of memory system performance are generally bandwidth and latency . Some memory system design changes improve one at the expense of the other, and other improvements positively impact both bandwidth and latency. Bandwidth generally focuses on the best possible steady-state transfer rate of a memory system. Usually this is measured while running a long unit-stride loop reading or reading and writing memory. See the STREAM section in [link] Chapter 15 for measures of memory bandwidth. Latency is a measure of the worst-case performance of a memory system as it moves a small amount of data such as a 32- or 64-bit word between the processor and memory. Both are important because they are an important part of most high performance applications.

Because memory systems are divided into components, there are different bandwidth and latency figures between different components as shown in [link] . The bandwidth rate between a cache and the CPU will be higher than the bandwidth between main memory and the cache, for instance. There may be several caches and paths to memory as well. Usually, the peak memory bandwidth quoted by vendors is the speed between the data cache and the processor.

In the rest of this section, we look at techniques to improve latency, bandwidth, or both.

Large caches

As we mentioned at the start of this chapter, the disparity between CPU speeds and memory is growing. If you look closely, you can see vendors innovating in several ways. Some workstations are being offered with 4- MB data caches! This is larger than the main memory systems of machines just a few years ago. With a large enough cache, a small (or even moderately large) data set can fit completely inside and get incredibly good performance. Watch out for this when you are testing new hardware. When your program grows too large for the cache, the performance may drop off considerably, perhaps by a factor of 10 or more, depending on the memory access patterns. Interestingly, an increase in cache size on the part of vendors can render a benchmark obsolete.

Simple memory system

This figure shows a large box, Memory, and a small box, Cache, both with sets of arrows pointing at a box labeled CPU. The memory box and the cache box, on their left sides, have narrow single arrows pointing at CPU, with the caption to the right, Latency equals single trip delay. The memory and cache boxes, on their right side, each have a grouping of four arrows pointing down at the CPU, with the caption to the side, Bandwidth equals Maximum Throughout.

Up to 1992, the Linpack 100×100 benchmark was probably the single most- respected benchmark to determine the average performance across a wide range of applications. In 1992, IBM introduced the IBM RS-6000 which had a cache large enough to contain the entire 100×100 matrix for the duration of the benchmark. For the first time, a workstation had performance on this benchmark on the same order of supercomputers. In a sense, with the entire data structure in a SRAM cache, the RS-6000 was operating like a Cray vector supercomputer. The problem was that the Cray could maintain and improve the performance for a 120×120 matrix, whereas the RS-6000 suffered a significant performance loss at this increased matrix size. Soon, all the other workstation vendors introduced similarly large caches, and the 100×100 Linpack benchmark ceased to be useful as an indicator of average application performance.

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
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Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
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