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» Extremely fast for large memory sizes

» Cost per bit is 5-10 times that of a “normal” RAM cell

» Example: some cache memory units.

2. types of memory

Computer memory system consists a various types of memory. Manufactures produce a number of different types of memory devices having a variety of technologies. The technology affect not only the operating chracteristics but also the manufacturing cost. In the section following we present an overviews of types of memory. You can see the study in detail of memory in the modules 10, 11 and 12.

  • Main Memory (“Internal” memory components)

- RAM (read-write memory): Static RAM, Dynamic RAM

- ROM (Read Only Memories) : ROMs, PROMs, EPROMs, EEPROMs, Flash Memory.

  • Cache memory

The cache memories are high-speed buffers for holding recently accessed data and neighboring data in main memory. The organization and operations of cache provide an apparently fast memory system.

  • External Memory

- Magnetic disks

- RAID technology disks

- Optical disks

- Magnetic tape

3. memory hierarchy

3.1 memory system organization

No matter how big the main memory, how we can organize effectively the memory system in order to store more information than it can hold. The traditional solution to storing a great deal of data is a memory hierarchy.

  • Major design objective of any memory system:

– To provide adequate storage capacity at

– An acceptable level of performance

– At a reasonable cost

  • Four interrelated ways to meet this goal

– Use a hierarchy of storage devices

– Develop automatic space allocation methods for efficient use of the memory

– Through the use of virtual memory techniques, free the user from memory management tasks

– Design the memory and its related interconnection structure so that the proces

3.2 multilevel memories organization

Three key characteristics increase for a memory hierarchy. They are the access time, the storage capacity and the cost. The memory hierarchy is illustrated in figure 9.1.

Figure 9.1. The memory hierarchy

We can see the memory hierarchy with six levels. At the top there are CPU registers, which can be accessed at full CPU speed. Next commes the cache memory, which is currently on order of 32 KByte to a few Mbyte. The main memory is next, with size currently ranging from 16 MB for entry-level systems to tens of Gigabytes. After that come magnetic disks, the current work horse for permanent storage. Finally we have magnetic tape and optical disks for archival storage.

  • Basis of the memory hierarchy

– Registers internal to the CPU for temporary data storage (small in number but very fast)

– External storage for data and programs (relatively large and fast)

– External permanent storage (much larger and much slower)

Figure 9.2 Typical Memory Parameters

  • Characteristics of the memory hierarchy

– Consists of distinct “levels” of memory components

– Each level characterized by its size, access time, and cost per bit

– Each increasing level in the hierarchy consists of modules of larger capacity, slower access time, and lower cost/bit

4. memory performance

Goal of the memory hierarchy. Try to match the processor speed with the rate of information transfer from the lowest element in the hierarchy.

  • The memory hierarchy speed up the memory performance

The memory hierarchy works because of locality of reference

– Memory references made by the processor, for both instructions and data, tend to cluster together

+ Instruction loops, subroutines

+ Data arrays, tables

– Keep these clusters in high speed memory to reduce the average delay in accessing data

– Over time, the clusters being referenced will change -- memory management must deal with this

  • Performance of a two level memory

Example: Suppsose that the processor has access to two level of memory:

– Two-level memory system

– Level 1 access time of 1 us

– Level 2 access time of 10us

– Ave access time = H(1) + (1-H)(10) ns

where: H is a fraction of all memory access that are found in the faster memory (e.g cache)

Figure 9.3. Performance of a two level memory

Questions & Answers

so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
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SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
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Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
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Porter
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I'm interested in nanotube
Uday
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what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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AMJAD
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AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
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Prasenjit
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Damian
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Azam
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Uday
I'm interested in Nanotube
Uday
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Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
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