RAM

[Manny]

i have just recently added 2GB of ram on my desktop so i have 4GB total... my
bios indicates and recognizes the additional ram but when i look at the
properties on the xp it only shows 2.87 GB of ram why is that?

 

[Shenan Stanley]

i have just recently added 2GB of ram on my desktop so i have 4GB
total... my bios indicates and recognizes the additional ram but
when i look at the properties on the xp it only shows 2.87 GB of
ram why is that?

You are not running a 64-bit operating system that has the ability top
actually utilize more of the RAM for your purposes.

Google for:

32-bit operating system 4GB limit

See what comes up. Some will probably come along and give you more specific
links - but the short answer remains the same...

You are running a 32-bit consumer Windows operatings system and the memory
limit exists at 4GB and the usage within the 2.5GB-4GB is consumed by
overhead dependent on several factors. You can expect to 'see' 2.5GB-3.5GB
of usable memory if you are running Windows XP 32-bit and have 4GB of
physical memory.

Also - not many people will see much usage/benefit above 1GB - much less
2-4GB of total memory in Windows XP without the use of high-end video
editing, musical editing, high-end calculations or virtual machine usage.
Having said that, purchasing 4GB at under $100 isn't really that much of a
waste. hah

 

[Paul]

i have just recently added 2GB of ram on my desktop so i have 4GB total... my
bios indicates and recognizes the additional ram but when i look at the
properties on the xp it only shows 2.87 GB of ram why is that?

Address space limitations. You have 4GB of memory, and you also have one
very large or two normal memory sized video cards. The whole
lot, must fit into a 4GB address space on 32 bit WinXP. They take care
of the video card needs first, and whatever is left over, becomes addresses
for the memory. So in this case, 2.87GB of address space was left for memory.

Rest of Memory --- 4.00GB \
\---- Cannot be accessed.
Top_Of_Memory_Register --- 2.87GB /

(Beginning of memory) --- 0.00GB

The memory is there, but there is no way to address it. Any address the
processor generates, will not "hit" the inaccessible region.

I don't know for a fact, you have two video cards. You might have
one video card, with 1GB of onboard memory. If you have two video
cards of 512MB each, try unplugging one of them, then check the
free memory again. It should grow a bit. And if you happen to
have some old video card, like a 32MB PCI video card from years
ago, give it a try. You'll see a lot more of your memory come back.
For people who value total memory, over the ability to game,
a cheesy PCI video card from long ago is the answer. It will
have a smaller addressing requirement, than today's cards with
their ridiculous onboard memory sizes. ( What good is a dog
slow video card, with 1GB of memory on it ? And yet, they make
some like that. )

HTH,
Paul

 

[Tim Slattery]

i have just recently added 2GB of ram on my desktop so i have 4GB total... my
bios indicates and recognizes the additional ram but when i look at the
properties on the xp it only shows 2.87 GB of ram why is that?

You're running a 32-bit operating system. It has a 32-bit address
space, which translates to 4GB that it can access. Some of that
address space must be used to access the memory on your video card, in
your BIOS, etc. What's left over is used for system RAM. The only
solution is 64-bit computing.

See http://members.cox.net/slatteryt/RAM.html for a longer discussion.

 

[Ken Blake, MVP]

i have just recently added 2GB of ram on my desktop so i have 4GB total... my
bios indicates and recognizes the additional ram but when i look at the
properties on the xp it only shows 2.87 GB of ram why is that?

Because you added more memory than you could use (see below). It's
also likely that even if you could use that much you would see no
improvement in performance by having that much. How much you can make
effective use of depends on what apps you run, but even 2GB is more
than more than most people need.

All 32-bit client versions of Windows (not just Vista/XP/7) have a 4GB
address space (64-bit versions can use much more). That's the
theoretical upper limit beyond which you can not go.

But you can't use the entire 4GB of address space. Even though you
have a 4GB address space, you can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and is not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but can
range from as little as 2GB to as much as 3.5GB. It's usually around
3.1GB.

Note that the hardware is using the address *space*, not the actual
RAM itself. If you have a greater amount of RAM, the rest of the RAM
goes unused because there is no address space to map it to.

 

[Unknown]

On Mon, 21 Sep 2009 21:08:01 -0700, Manny


Note that the hardware is using the address *space*, not the actual
RAM itself. If you have a greater amount of RAM, the rest of the RAM
goes unused because there is no address space to map it to.

Once again, doesn't DMA (hardware) use actual RAM itself?

 

[HeyBub]

i have just recently added 2GB of ram on my desktop so i have 4GB
total... my bios indicates and recognizes the additional ram but when
i look at the properties on the xp it only shows 2.87 GB of ram why
is that?

Raise 2 to the 32nd power and subtract 1.

Show your work.

 

[Bob I]

Once again, doesn't DMA (hardware) use actual RAM itself?

DMA is a data transfer procedure, it doesn't use RAM, it reads and
writes to the RAM that is addressable below those addresses pre-empted
by installed hardware.

http://en.wikipedia.org/wiki/Direct_memory_access

 

[Unknown]

I know exactly what DMA is. But, isn't it a fact you cannot store any
programs in the area that is used for input?
Therefore, that area is subtracted from total memory?

 

[Bob I]

Store programs?!?!?! If I understand your question correctly, then yes
those addresses assigned to hardware are what we are talking about. DMA
will transfer data from/to the System memory to/from the hardware
addresses.

 

[Unknown]

Exactly! The question comes up many times about installing 4 gigs but only
approximately 3.1 gigs is usable.
Isn't the memory DMA uses subtracted from the 4 gigs to get to the 3.1 gig
figure?
I.E. Ken always says actual memory is not used. Read his response.

 

[Bob I]

DMA is a data transfer method, it doesn't USE memory. A 32 bit operating
system can communicate directly with 4GB address locations. The hardware
is addressed starting at the top of the listing, while memory (RAM) is
addressed starting at the bottom. When the 2 lists meet, that is the
limit of usable RAM. Lets say you put in the full 4 GB of memory sticks.
And lets say the two list meet at 3.1 GB. That is your usable memory.
Add more hardware, say a second video card, the top list extends down
further and now they meet at 2.7 GB. Take that new card back out and it
moves back up to 3.1 GB. Remove the other high-end video card and
replace it with some low end unit, now you have 3.5GB of usable memory.

 

[Jim]

Windows, as well as many other operating systems, use what is known as
memory mapped i/o. That term means that the control registers for i/o
controllers in the controllers are accessed as if they are physical memory.
It also seems that the physical memory which resides in a graphics interface
card is also accessed that way. Windows, during system startup, does not
allow physical memory in the computer to overlap the memory mapped i/o
space. The result is that Windows can only reference around 3GB of the
possible 4GB memory.
The server systems from MS use the /PAE switch which allows additional
physical memory. Home systems do not; hence the solution for Home users is
a 64bit computer.
Jim

 

[Unknown]

If a hard disk is using DMA where does the data go? Am I really that far
behind on technology advances?

 

[Unknown]

Please read my above response to Bob I and tell me what I am missing.
Perhaps I'm confused.
If a hard disk is given a read command and DMA is being used, where is the
data going?

 

[Bob I]

The data is written to the user memory area. Same place it would go if
it were using PIO, except the CPU doesn't have to babysit the transer,
so it is a heck of a lot faster. ;-)

 

[Unknown]

OK so far! Isn't that space where the data goes unusable for programming?
I.E. If one has 4 gigs of memory installed, isn't that space unusable and
subtracted from
the 4 gig to arrive at the approximate 3.1 gig of addressable memory?
Read Kens response below---(Doesn't the hardware use 'actual RAM?)

Note that the hardware is using the address *space*, not the actual
RAM itself. If you have a greater amount of RAM, the rest of the RAM
goes unused because there is no address space to map it to.

Ken Blake, Microsoft MVP (Windows Desktop Experience) since 2003
Please Reply to the Newsgroup

 

[Bob I]

No, no, no, that is the 3.1 usable memory area. Data is the programs,
you are running like word, internet explorer, games whatever, the letter
you typing in word, the picture you paste into the word document. They
all go into user memory or RAM.

 

[Unknown]

I guess you don't understand me. I'm not a great linguist.
Could you explain this comment?

""The hardware is only using 'address space' not the actual RAM itself"".
In the case of DMA doesn't the 'hardware' use RAM?

 

[Bob I]

There are 4 gigabytes of addresses available in a 32 bit operating
system. Those addresses are used to communicate with components in a PC.
Only one of those components is RAM or memory. The others are the PCI
bus, video cards, network cards, sound cards etc. etc. You can't give
the same address to two things(unless special software is used) so,
memory gets the low addresses, non-memory gets the high addresses, where
the two meet the non-memory get to use the address and the RAM that is
installed will be ignored. FORGET about "DMA", it has NOTHING to do with
what this is all about.