T500 4GB RAM

[winstonli]

I have a T500 with 4GB RAM installed runing Vista 32 bit. When I check properties on computer, it shows "memory (RAM): 4.00 GB, but when I check Task Manager, Performance, it shows:
Physical Memory (MB)
Total 2519
Cached 1382
Free 19
Why total is only 2519MB?
and at the bottom of Task Manager, it shows the physical memory usage is constantly around 50%. That means it used 2 GB ram, is that true? How could the vista used 2 GB ram while the standard model of T500 currently comes with 2 GB RAM only.

[winstonli]

I found out the reason myself. It's because 32 bit windows cannot use all 4GB RAM. But it's more confusing because 32 bit op can address 4GB RAM max. So why can't I have all 4 GB? I posted this question at the Windows Vista section because it is a Vista problem.

[bill bolton]

So why can't I have all 4 GB?

Its an intrinsic limitation of 32 bit desktop OSs. See this thread in the T6x forum here for lots of detail... T60/T61/p memory limitations -- the definitive answer [pics]

Cheers,

Bill B.

[HankB]

In addition to the information referenced by Bill B. I thought I'd add my experience with a T500 and a couple versions of Linux as well as some ruminations on what happens to the rest of the 4GB address space.

First, 32 bit addresses can address 4GB RAM. the only way to address more (with a 32 bit Intel or similar processor) is to add some additional address bits elsewhere (PAE I suppose does this.)

Aside form the RAM, the computer must address other I/O devices such as the PCI bus, video card and probably other devices such as chip set control registers. These also fit into that 4G address space. Often times these are spread around that upper (or lower) address space so a few K or few M of registers and such are probably spread about a much larger space. In addition to this, some laptop video cards use system RAM instead of having their own dedicated memory. (I don't know if that's the case with any Lenovo laptops.) That's a brief description of the "why."

I bumped my T500 up to 4GB because I can. And (going through another reliable vendor) was a lot cheaper than the Lenovo upgrade. Using Memtest86+ the speed of one stick of the new memory is reported at 3186 MB/s which matches the factory RAM. With two sticks, this went up to 3529. That's nearly an 11% bump in apparent memory bandwidth, but will only come into play on cache misses so the actual effect will be overall increases memory throughput of probably about 1% (assuming a 90% cache hit rate - not unreasonable.)

The preinstalled Vista Home Basic reports about 3GB RAM. I probably have a higher number than you because I do not have the dual graphics and guess that you do. I'm sure the % usage that Vista reports is based on the memory it sees and not the total installed since it does not know about anything beyond about 3 GB.

The 32 bit Ubuntu 8.10 Live CD seems to recognize the same amount of RAM.

The 64 bit Linux kernel that installs/upgrades with Ubuntu 8.10 (2.6.27) reports the full 4 GB of RAM as would be expected.

At present I have to suggest that the bump from 1-2 GB is well worth the money because it provides more working room for either Linux or Vista. Expanding beyond that reaps diminishing returns unless you have some tremendously memory consuming programs to run.

If you are running a 32 bit OS, I wonder if it is even worth the expense to go beyond 2 GB. But w/out dual graphics, at least you can gain about another 50%.

Despite the low present memory utilization I have no regrets about spending the extra $$$ to go to 4GB. That should leave me lots of room to grow over the expected life time of this laptop and those times when I do something that requires more RAM the system sill handle it with ease. (And those buggy programs with memory leaks will run that much longer before they bring the system to its knees. )

best,
hank

[Aroc]

The available physical memory that Windows XP x86 and Windows Vista x86 can use has been limited to approx 3GB for compatibility reasons. In fact, if you are running a x86 OS, you are probably doing so for compatibilty reasons (otherwise you'd be running Windows Vista x64, right , right? ). Supporting a wide range of add-on devices and the corresponding drivers is important to Windows XP x86, limiting use of memory to the 3GB level, is a reasonable trade-off for broad hardware support. MS had a technical article about this a few years back (SP2 or SP1a days?) that I vaguely recall.

http://support.microsoft.com/kb/888137

For example, before you upgrade to Windows XP SP2, the System Properties dialog box may report approximately 3.87 GB of RAM. The System Information tool may report that the total physical memory is approximately 3,540.00 megabytes (MB). After you upgrade to Windows XP SP2, the System Properties dialog box may report approximately 3.12 GB of RAM, and the System Information tool may report that the total physical memory is approximately 2,770.00 MB.

This issue occurs because of a design change in Windows XP SP2 that is also included in Windows Vista. The changes were made to PAE mode behavior to improve driver compatibility.

To reduce driver compatibility issues, Windows Vista and Windows XP Service Pack 2 include hardware abstraction layer (HAL) changes that mimic the 32-bit HAL DMA behavior. The modified HAL grants unlimited map registers when the computer is running in PAE mode. Additionally, the kernel memory manager ignores any physical address that is more than 4 GB. Any system RAM that is more than the 4 GB barrier would be made unaddressable by Windows and be unusable in the system. By limiting the address space to 4 GB, devices with 32-bit DMA bus master capability will not see a transaction with an address that is more than the 4 GB barrier. Because these changes remove the need to double-buffer the transactions, they avoid a class of bugs in some drivers that is related to the correct implementation of double buffering support.

Something had to give. Supporting physical RAM above the 3GB amount wasn't deemed as important as maintaining existing driver and hardware support. I believe MS made a good decision here given the majority of users and needs. Though that hasn't (and rightfully so!) silenced the outcry from the enthusiast community.

[comptiger5000]

They could have easily implemented PAE on XP x86 and Vista x86 for 4gb+ RAM support. They just didn't want to. They did it in Server 2003 and 2008 x86, and the corresponding XP and Vista drivers for every piece of hardware I've ever tried work fine, even on systems with 4gb+ of RAM in use.