Computer RAM

[physics kiddy]

Today, while I was exploring my system properties, I found that my computer shows only 0.99 Mb RAM. But I have 1 GB of RAM and I have Windows XP SP2. Why does computer show 0.99 Mb ?

 

[Greg Bernhardt]

Today, while I was exploring my system properties, I found that my computer shows only 0.99 Mb RAM. But I have 1 GB of RAM and I have Windows XP SP2. Why does computer show 0.99 Mb ?

You are sure it is Mb and not Gb?

 

[physics kiddy]

I am really sorry. It's GB. Why does it show only 0.99 and not 1 GB ?

 

[DaveC426913]

I am really sorry. It's GB. Why does it show only 0.99 and not 1 GB ?

1Gb is not 1000Mb; it's 1024Mb. It may be reporting one or the other.
A sector may have gone bad, and your system have have dropped it from use.
A dozen other reasons, none of which mean you need to worry about it.

 

[rcgldr]

Try clicking on start / run / then enter msinfo32 to run msinfo32.exe and see what it reports for your memory size. I'm not sure what system properties is reporting when it reports ram size, but it could be subtracting part of the operating system's overhead (like mapping tables for virtual memory) from available ram.

 

[physics kiddy]

My bro says that sometimes it happens that OS is not able to make use of the total available memory and so it shows 0.99 GB.

Meanwhile, what is the difference between Virtual and Physical Memory ?

 

[DaveC426913]

Meanwhile, what is the difference between Virtual and Physical Memory ?

RAM is active memory use by the computer while running programs. Virtual memory is what it creates when it doesn't have enough RAM; it uses disk space as if it were RAM. Essentially it creates a big swap file containing pages that it swap in and out of RAM quickly. Usage of disk space this way is faster than usage as storage, but it's only temporary - while programs are running.

Virtual memory is slower than RAM but faster than disk memory.

I've been building a cedar plank carport recently.

My workroom = disk storage - everything is organized with a permanent location - but I have to go inside to get it
My worktable in the driveway = RAM - what I am working on right now - the chop saw
My picnic table = virtual memory - I ran out of room on my worktable (because the chopsaw is huge), so all my other tools need a place to sit when I'm using the chopsaw. And I don't want to have to go downstairs to the workroom every time I need a hammer and nail. The picnic table is quick but tempory access.

 

[rcgldr]

wiki articles:

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

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

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

http://en.wikipedia.org/wiki/Content-addressable_memory

 

[physics kiddy]

are wiki articles always reliable ? Someone told me wikis have 90% false information .... is that true ?

 

[DaveC426913]

are wiki articles always reliable ? Someone told me wikis have 90% false information .... is that true ?

No. What a silly thing for your friend to say. They are guilty of the very thing they accuse wiki of doing - spreading false information.

Wiki is a great point of first contact for lots of information. It can be very useful for the level a layperson might be interested in - like your question. It's also a good jumping off point for further reading. There are links at the bottom to sources.

What you don't want to do is use it exclusively, and rely on it to be accurate when reliability on accuracy is critical, such as when writing a paper.

It is a great encyclopedia on virtually everything; it is not an authority on anything.

 

[physics kiddy]

Since everything is editable in Wikipedia, I guessed someone might write false info. That's why I never consulted Wikipedia for getting info.

 

[DaveC426913]

Since everything is editable in Wikipedia, I guessed someone might write false info. That's why I never consulted Wikipedia for getting info.

Yes, it is always a risk. But Wiki is self-monitoring. Someone's false info will last for a very short time before ten other contributors descend upon it and remove it or correct it.

 

[rcgldr]

The main thing missing from the wiki artlicle list I posted before is dealing with page fragmentation. Intel uses a page size of 4k (or 4MB but I'm not aware of any OS using this). For applications that run continously, continuous allocation and freeing of small amounts of memory, including stuff automatcally allocated and freed by windows for user interface stuff, can result in only portions of each 4K page being used. Eventually the application runs out of those pages, which Windows will report as out of memory, even though the application is only using about the same amount of memory. Windows .NET framework includes a garbage collector to avoid this issue, but then the application has to allocate and access memory based objects via .NET roots (pointers to pointers to objects) in order for the garbage collection feature to operate. The application also ends up getting paused during garbage collection cycles, so this scheme wouldn't work in real time environment unless a second real time task wasn't based on .NET and instead sent messages to the primary app which would queue messages when it was paused. Wiki article:

http://en.wikipedia.org/wiki/.NET_Framework#Memory_management

For Microsoft Visual Studio, garbage collectable objects are allocated via handles with gcnew instead of new, and in C++, handles are declared using '^' instead of '*', for example: MyClass ^ p_MyClass = gcnew MyClass; . (The old syntax for '^' was '__gc *' (VC 2002 and 2003)).

 

[DaleSwanson]

Since everything is editable in Wikipedia, I guessed someone might write false info. That's why I never consulted Wikipedia for getting info.

I find it odd that you wouldn't trust Wikipedia, but would trust a forum (ie Physics Forums). In both cases anyone can write anything. In both cases people tend mostly write accurate information, and point out and correct incorrect information.

 

[DirectCurrent]

May be its not showing 1GB because its reserved for video memory...

 

[chroot]

DirectCurrent is right, some portion of the 1 GB of main RAM is being used for video memory. This has nothing to do with paging or anything else.

- Warren

 

[rcgldr]

video ram - unless the motherboard has an onboard video card that shares the main ram for it's video then the ram isn't being used by the video card.

If you click on start, run, msinfo32 (to run msinfo32.exe), then click on memory, it will display a map of all the address space on your computer, including the main ram, and any memory address space used by the hardware on your computer.