Patrick J. Kidd

RAM = Memory
Random Access Memory

Memory and Performance: The Bottom Line - Recommendations - Reviews by ExtremeTech
- It appears from these tests, and from subjective observations, that you're more likely to benefit from an increase in memory capacity than you are with an increase in either DDR level (so hold off on that motherboard upgrade, if that's the only reason you were going to do it) or frequency (so you might want to reconsider that memory overclock, too).
  The bottom line: If you're going to spend money on memory-contingent upgrades, buy more, not faster, memory.
Types of RAM
- DRAM (dynamic random access memory)
- FPM-RAM (fast page mode)
- EDO-RAM (enhanced data out)
- SDRAM (synchronous) (PC66, PC100, PC133)
- FSRAM (fast static)
- RDRAM (Rambus DRAM) (PC600, PC700, PC800, PC1066), RIMM (Rambus in-line memory modules) (1060MHz)
- DDR-DRAM (double-data rate) 333MHz, 667MHz, 800MHz
  - DDR-2/3/4/5/6/7/etc?
- CAMM
  - CAMM Memory Modules Are Coming to Desktops | Extremetech
  - Compression Attached Memory Module - Wikipedia

Limits

Remember that a 32-bit operating system (like Windows XP Pro) can address 32 bits of physical address space only a maximum of 2³² bytes (= 4GB).
However, a 32-bit OS usually refuses to recognize more than 2 GB. You will never get more than about 3.12 GB.
Windows XP/Vista 32-bit and 4GB ram problem

RAM Allocation

2³² = 4,294,967,296 = 4 GB
- PCI memory address space is used to transfer data by the BIOS, I/O cards, networking, PCI hubs, bus bridges, PCI Express, and graphics cards.
- PCI will take up at least 512 MB, leaving between 3 and 3.4 GB
To go beyond the 4-GB limit, a processor must have greater than 32-bit addressing. There are two ways of accomplishing this: PAE and 64-bit processing.
- Physical Address Extension (PAE) is a mode allowing a 32-bit x86 processor to use an additional 4 bits for addressing, creating a 36-bit address:
  2³⁶ = 68,719,476,736 = 64 GB
- A 64-bit capable x86 processor, such an Intel Pentium 4 with EM64T, uses 64-bit addressing. This processor can run 64-bit OSes.
  2⁶⁴ = 18,446,744,073,709,551,616 = 16 EB (exabyte 1018)
Note: Do not confuse total physical memory and memory addressing with the amount of virtual memory available to the OS. No matter how much physical memory is in the system, a 32-bit OS will have 4 GB of virtual memory through paging.

Windows Memory Has Physical, Design, and Marketing Limitations
Posted by Dave Methvin, Jul 25, 2008 03:40 PM
Mark Russinovich is one of Microsoft's best technical people, and he shows that every time he makes a blog post. This week he has a great post about the maximum supported memory in different versions of Windows. I thought I knew this story pretty well by now, but learned several new things about the limits--and the interesting reasons behind them.
The blog points to an MSDN article on memory limits, which does have a few quirks. As the commenter on that page points out, why should 64-bit Windows Vista Business (a desktop OS) allow 128 GB of RAM, but 64-bit Windows Server 2008 Standard top out at 32 GB? These are not limits born of technical reasons, but simply put there by the marketing department to convince one group or the other to pony up more money for what is essentially the same OS.
There is a way for 32-bit Windows to access memory using a technology called Physical Address Extensions (PAE). However, Microsoft intentionally limited desktop XP and Vista to 4 GB of RAM because many third-party drivers did not work properly when trying to access a memory address above 4 GB. Rather than risk crashes and system problems, Microsoft made it impossible to do.
This issue is compounded by hardware, particularly video boards, that map some of their memory into the 4 GB address space. Windows can do that fine, but in the process it maps some real RAM into the space above 4 GB where it won't be accessed by either applications or the operating system itself. That's why you'll often see Windows use much less than 4 GB RAM on 32-bit XP or Vista, even if you've installed 4 GB of physical memory.
I completely understand why Microsoft instituted the 4-GB limit for 32-bit desktop operating systems by default, but the finality of the implementation leaves something to be desired. Since this was ostensibly a patch to work around bad device drivers, it would have been good to have perhaps a boot.ini option that technical users could use to regain their missing memory. If I have well-behaved drivers, I should be able to use them with more than 4 GB on 32-bit Window -- or at the very least, get a full usable 4 GB of RAM.
One point that Russinovich didn't emphasize, perhaps because it's a hardware problem and not a Microsoft problem: many Pentium 4 northbridge chipsets for portables and desktops were limited until recently to addressing 4 GB of RAM. Even if you install a 64-bit version of Windows on these systems, you won't be able to install more than 4 GB of RAM, so it doesn't help much. Server chipsets allow a more generous helping of RAM as you might expect.

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RAMBOOSTER - Monitors and frees Random Access Memory