Hardware Reference
In-Depth Information
Unfortunately, most standard PC processors, motherboards (chipsets), and memory mod-
ules don't support ECC. If you want a system that supports ECC, make sure all the
components involved support ECC. This usually means purchasing more expensive pro-
cessors, motherboards, and RAM designed for server or workstation applications.
RAM Upgrades
Adding memory to a system is one of the most useful upgrades you can perform and also
one of the least expensive—especially when you consider the increased performance of
Windows, Linux, and their applications when you give them access to more memory. In
some cases, doubling the memory can practically double the speed of a computer.
But it doesn't always pay to go overboard because adding memory that you don't really
need will cost money and power, and you will gain little or nothing in speed. The best
philosophytotakewhenaddingRAMtoacomputeristhat“moreisbetter,uptoapoint.”
IfyourunWindowsXP,youshouldspecifya
minimum
of256MB,andpreferably512MB
to 1GB or more depending on the chipset, processor, and especially the applications you
intend to run. If you run 32-bit Windows 7 or Vista, the
absolute minimum
should be
512MB according to Microsoft, but I recommend a minimum of 1GB, with 2GB to 3GB
preferred. 64- bit versions of Windows 7 and Windows Vista have a 2GB minimum, but
perform better with 4GB or more of memory.
Maximumphysicalmemorycapacityisdictatedbyseveralfactors.Thefirstistheamount
addressablebytheprocessoritself,whichisbasedonthenumberofphysicaladdresslines
in the chip. The original PC processors (8086/8088) had 20 address lines, which resulted
in those chips being able to recognize up to 1MB (2
20
bytes) of RAM. The 286/386SX
increased memory addressing capability to 24 lines, making them capable of addressing
16MB (2
24
bytes). Modern x86 processors have from 32 to 36 address lines, resulting in
from 4GB to 64GB of addressable RAM. Modern x86-64 (64-bit) processors have 40 ad-
dress lines, resulting in a maximum of 1TB (1 terabyte) of supported physical RAM.
See
“
Processor Specifications
,
”
p.
37
(
Chapter 3
)
.
The operating mode of the processor may place further limits on memory addressability.
For example, when the processor is operating in backward-compatible real mode, only
1MB of memory is supported.
See
“
Processor Modes
,”
p.
45
(
Chapter 3
)
.
Note that even though modern 64-bit processors can technically address up to 1TB, mod-
ern motherboards or chipsets generally limit the maximum amount of RAM to 8GB,
16GB, or 24GB. The type of software also has an effect. The 32-bit versions of Windows
XP, Vista, and Windows 7 limit memory support to 4GB (with only about 3.25GB usable
