# What is the difference between Main memory and Secondary memory?



## allena

Please any body tell me the difference between main memory and secondary memory.


----------



## hermeslyre

Main memory would refer to the system RAM, a relatively fast portion of memory directly manipulated by the processor. Secondary memory is an old term methinks, refering to the storage medium. Hard drives, stuff like that.


----------



## allena

Sorry but its not clear to me.
Please tell me what actually the work of main memory?


----------



## hermeslyre

Main memory is the memory that is able to communicate directly with the CPU, secondary memory cannot. Main memory's job is thusly that; to act as emissary to the secondary memory.

To put it plainly, anything the CPU requires off secondary memory (say a hard drive) must first be loaded onto the main memory to be used by the CPU.


----------



## AMD Fanboy

The difference is that there is no such thing as secondary memory. It's either System Memory, or it's Hard Drive Space. Each one does something COMPLETELY different. People just tend to call the Hard Drive Memory because it "Remembers" Information. In any event, the hard drive is NEVER Memory. If you're lacking enough actual memory to do the job, the hard drive can sometimes host space for a page file. it allows the system to write to a pre-allocated space when it runs out of actual memory for a temporary amount of time. since the hard drive is slower than memory, this really doesn't help performance all that much. it's better to go out an buy more memory when you see alot of hard drive paging. Let me list some of the things that memory and Hard Drives so different.


Hard Drive: 
1 Will have ALOT more capacity. Up to 1 Terabyte
2 Is SLOW compared to System Memory
3 It has Moving Parts
4 It is sensitive to Movement and Shock
5 Is NOT required for your computer to boot.
6 Information is Retained when the computer is Turned off.

Memory:
1 Usually comes in DIMMs (Dual Inline Memory Module) that are 2GB or Less
2 Is alot faster than a Hard Drive
3 Has NO MOVING PARTS
4 Is Unaffected by movement or shock
5 Is required for a successful Boot.
6 does not store information when the computer is off.

A hard drive is nothing more than storage. it's like a closet. Memory is like scratch paper for your CPU. It's a Buffer really. Your CPU is faster than your Hard Drive is, so there are alot of programs that will have information PreFetched into memory. this way the CPU will have it right when it's needed rather than having to wait for the Hard Drive to find that information. In the future, long term storage will all be in the form of actual memory, but right now it's too expensive to implement. Hard Drives are the last major bottle neck of computer performance. the next time someone says something about primary and secondary memory, you have my permission to call them an Idiot.


----------



## StrangleHold

allena said:


> Please any body tell me the difference between main memory and secondary memory.


 
Simple answer. You probably are saying the term secondard memory but really mean virtual memory. When your system runs out of physical memory/ram it will use a set amount of space on your harddrive as virtual memory. Bump it up one and the fastest memory is on your processor as cache.


----------



## Sir Travis D

@amd fanboy, not all hard drives have moving parts. SSD's don't.


----------



## AMD Fanboy

no, SSDs are not a type of hard drive, they're Memory. that's what makes them so quick. Besides, you don't have a SSD in your computer unless you've got deep pockets. When SSDs are commonplace, i won't object to the terms Primary and Secondary Memory, However, those terms will be used as you would use Primary and secondary hard drive. there's still only one system memory and it's used in an entirely different way.


----------



## Geoff

AMD Fanboy said:


> no, SSDs are not a type of hard drive, they're Memory. that's what makes them so quick. Besides, you don't have a SSD in your computer unless you've got deep pockets. When SSDs are commonplace, i won't object to the terms Primary and Secondary Memory, However, those terms will be used as you would use Primary and secondary hard drive. there's still only one system memory and it's used in an entirely different way.


Not necessarily, it depends on your definition of a hard drive.

_Hard Drive:_ A rigid non-removable disk in a computer and the drive that houses it. Hard disks store more data and can be accessed quicker than floppy disks.


----------



## Sir Travis D

Well AMD SSD's are hard drives. They store permanent information, like documents, boot information, just like a normal hard drive.


----------



## AMD Fanboy

[-0MEGA-];1005289 said:
			
		

> Not necessarily, it depends on your definition of a hard drive.
> 
> _Hard Drive:_ A rigid non-removable disk in a computer and the drive that houses it. Hard disks store more data and can be accessed quicker than floppy disks.




You have Disproven yourself actually. Your own definition talks about a non-removable DISK, and then it refers to a hard DISK. I guess a solid state drive could be in the form of a disk. it would just be alot harder to mount in a 3.5" drive bay.

This really is like the whole Engine Vs Motor Argument. Most cars have an engine, but everyone calls it a Motor. It's not really a motor. Motors Use Electricity and Engine Use Fuel. Of course, Nowadays, Cars can have both at the same time. They call them Hybrids.

In Computers, it's best to use correct terminology because you can confuse someone more than help them. On occasion i've had people refer to their Hard Drive as Memory and i didn't catch on to it right away. It would have saved time if they had said Hard Drive, but in most cases the reason was simply that they didn't know the differance. The Fact remains that Memory and Hard Drives are two completely differant things. Even when the time comes that every one is using solid state drives, they will be two completely differant types of memory. the system memory will be volatile, and the SSDs will be Non-Volatile.


----------



## tyttebøvs

If someone wanted, they could make a device that gets mapped into the CPU's address space, and stores its information on a regular harddrive. It would be slow as hell, but it would be addressable through the CPU's memory bus.

RAM, harddrives, solid state disks, they're just a way to store data, volatile or non-volatile.


----------

