Re: RAM capacity
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Subject: Re: RAM capacity
Date: 7/26/2008 8:02:38 AM (GMT-7)
IP Address: 220.127.116.11
In Reply to: RAM capacity posted by
This is primarily a reporting issue. The system sees 4 GB in the BIOS but the chipset, particularly the PCIe system reserves a portion of the memory address space to be excluded from use by the operating system.
So you have the full amount of RAM in your system but you lose 500 MB for shadow RAM. Moreover, as you said, any 32 bit OS has limitations. The limitations are though that you can only address 4 GB total that are divided into user and kernel memory on an address range from -2^31 to 0 and then 0 to +2^31 (signed and unsigned memory addresses), respectively
No matter how much memory you are running in your system, that means that the user memory cannot go beyond 2 GB. Effectively, it doesn't even matter if you have 2.5GB in your system or 4 GB, as long as you have the 500 MB for the reserved hardware shadows and the 2 GB for the user and/or kernel, the CPU's memory management unit can allocate whatever it needs for what on the fly out of that pool.
There is another issue with some chipsets, you need to enable memory remapping to get access to the full system memory density.
There is also the 3GB switch that allows applications that were compiled with the "large-memory-array" flag assigned to the complier to access actually 3 GB of user memory by shifting the address boundary between user and kernel memory, however, that switch causes compatibility issues with other applications.
Vista's ready-boost feature (since it was mentioned above) is about the most useless POS ever invented. IN fact, it causes up to 70% performance degradation in memory-intensive applications because the memory accesses are constantly interrupted to query the USB ports for data from Ready-Boost. It may have some merit in a case where you try to run Vista on 256 MB of system memory but in any other case, stay away from it.
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