memory limit by calculation

lets suppose a

32 bit computer...

in that each cell has 4 bytes...now a memory cell can only be accessed distinctly as it is a 32 bit computer o开发者_C百科nly

x=(2^32)-1 memory cells

can be addressed...so total no. of bytes is

y=x*4.

so the gigabytes come out to be

y/(1024^3)=16...

if only 16gb can be accessed how come we have 80 gb and even more memory computers which can access all data stored in the memory

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Your numbers are off - the minimum addressable unit is a byte, so the number of available bytes is:

x=(2^32)

or 4Gb. We can have larger sizes than this because we now have 64-bit architectures.

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AFAIK it's not typical for an OS to permit access to memory > 4GB for a 32-bit computer - at least, they don't make such access easy.

Check out AWE (Address Windowing Extensions) - Windows means of getting to > 4GB on a 32-bit box. SQL Server can be configured to use AWE to increase the memory available for certain operations.

Access to memory > 4GB is likely to come at a "high price" in terms of performance. If you want > 4GB RAM then your best bet is a 64-bit processor.