What is the difference between the main memory (RAM) and the cache memory in Computers?  

RAM is general purpose memory, used to store programs, data, graphics, etc. You want 64meg or so these days.

Cache is specialized memory used by the CPU to speed up access to the RAM. It acts as a buffer, "looking ahead" and trying to anticipate the next item needed from RAM. When it guesses right, the CPU keeps on running, full speed ahead. When it guesses wrong, then the whole machine stops and waits while the right data is found and brought to the CPU. 512K is a decent amount of cache these days; avoid machines with zero cache (e.g., the early Celerons).

One twist on the cache front is that the CPUs also have cache embedded right on the chip itself; these cache amounts are generally in the 16K - 64K range. This cache is called L1 (Level 1) cache, as opposed to the cache mentioned above (L2). Hope this helps...the cache issue, in particular, can be tricky... When talking about browsers and cache, the cache here is actually harddisk space used by the browser to store recently-used web pages. The idea is similar to the CPU cache in my last post; the idea being when you surf, you are more likely to use a web page that you've looked at in the past than you are to find a new page, so it stores them on disk, which is a lot faster to retrieve from than constantly resending the page over the net.

The tricky thing about this kind of cache is that the web page might have changed. Your browser preferences determine how often the browser checks to see if it has changed. Mine is set to "once per session"; I assume in the typical 30 minutes that I'm on that the web page has not changed. If you are using volatile pages, or stay on for hours and hours, you may want a different setting.

Pushing the 'reload' button, by the way, forces a refresh of the web page, so that if you are watching an auction, say, if you use this button, you will always get the latest page.


source

http://www.home1.gte.net/j ohnfull/n101.htm

Answered by Smarty at 2:38 PM on May 02, 2008

sujal RAM is general purpose memory, used to store programs, data, graphics, etc. You want 64meg or so these days.

Cache is specialized memory used by the CPU to speed up access to the RAM. It acts as a buffer, "looking ahead" and trying to anticipate the next item needed from RAM. When it guesses right, the CPU keeps on running, full speed ahead. When it guesses wrong, then the whole machine stops and waits while the right data is found and brought to the CPU. 512K is a decent amount of cache these days; avoid machines with zero cache (e.g., the early Celerons).

One twist on the cache front is that the CPUs also have cache embedded right on the chip itself; these cache amounts are generally in the 16K - 64K range. This cache is called L1 (Level 1) cache, as opposed to the cache mentioned above (L2). Hope this helps...the cache issue, in particular, can be tricky... When talking about browsers and cache, the cache here is actually harddisk space used by the browser to store recently-used web pages. The idea is similar to the CPU cache in my last post; the idea being when you surf, you are more likely to use a web page that you've looked at in the past than you are to find a new page, so it stores them on disk, which is a lot faster to retrieve from than constantly resending the page over the net.

The tricky thing about this kind of cache is that the web page might have changed. Your browser preferences determine how often the browser checks to see if it has changed. Mine is set to "once per session"; I assume in the typical 30 minutes that I'm on that the web page has not changed. If you are using volatile pages, or stay on for hours and hours, you may want a different setting.

Pushing the 'reload' button, by the way, forces a refresh of the web page, so that if you are watching an auction, say, if you use this button, you will always get the latest page.
for more inf check source www.home1.gte.net/johnfull/n101.htm - 3k

Answered by raj u at 1:53 PM on May 02, 2008

well sujal, Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory. Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor. An L1 cache is on the same chip as the microprocessor. (For example, the PowerPC 601 processor has a 32 kilobyte level-1 cache built into its chip.) L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip.

In addition to cache memory, one can think of RAM itself as a cache of memory for hard disk storage since all of RAM's contents come from the hard disk initially when you turn your computer on and load the operating system (you are loading it into RAM) and later as you start new applications and access new data. RAM can also contain a special area called a disk cache that contains the data most recently read in from the hard disk.

Answered by satyaiitk at 6:15 PM on May 01, 2008

Well,

Main Memory:-

Refers to physical memory that is internal to the computer.

The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

The computer can manipulate only data that is in main memory.

Therefore, every program you execute and every file you access must be copied from a storage device into main memory. The amount of main memory on a computer is crucial because it determines how many programs can be executed at one time and how much data can be readily available to a program.

Because computers often have too little main memory to hold all the data they need, computer engineers invented a technique called swapping, in which portions of data are copied into main memory as they are needed.

Swapping occurs when there is no room in memory for needed data. When one portion of data is copied into memory, an equal-sized portion is copied (swapped) out to make room.

Now, most PCs come with a minimum of 32 megabytes of main memory. You can usually increase the amount of memory by inserting extra memory in the form of chips.

While on the other hand cache memory Pronounced cash, a special high-speed storage mechanism.

It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.

A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory.

Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.

Some memory caches are built into the architecture of microprocessors. The Intel 80486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called Level 1 (L1) caches. Most modern PCs also come with external cache memory, called Level 2 (L2) caches. These caches sit between the CPU and the DRAM. Like L1 caches, L2 caches are composed of SRAM but they are much larger.

Disk caching works under the same principle as memory caching, but instead of using high-speed SRAM, a disk cache uses conventional main memory. The most recently accessed data from the disk (as well as adjacent sectors) is stored in a memory buffer. When a program needs to access data from the disk, it first checks the disk cache to see if the data is there. Disk caching can dramatically improve the performance of applications, because accessing a byte of data in RAM can be thousands of times faster than accessing a byte on a hard disk.

When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science.

Answered by ajay kumar at 7:26 AM on April 27, 2008

The RAM is th memory used to store temporarily all the porgram instructions and Data to be supplied to the processor for processing ( for all running programs ) , now the Cache is usually an additional and faster memory which sits between the RAM and the processors / storage devices to speed up processing / storage by storign the next sequential instructions / data for ready and faster access by the CPU / Storage devices .

Answered by Clayton at 12:07 AM on April 27, 2008

Cache memory is random access memory (RAM) that a computer microprocessor can access more quickly than it can access regular RAM. As the microprocessor processes data, it looks first in the cache memory and if it finds the data there (from a previous reading of data), it does not have to do the more time-consuming reading of data from larger memory.
Cache memory is sometimes described in levels of closeness and accessibility to the microprocessor. An L1 cache is on the same chip as the microprocessor. (For example, the PowerPC 601 processor has a 32 kilobyte level-1 cache built into its chip.) L2 is usually a separate static RAM (SRAM) chip. The main RAM is usually a dynamic RAM (DRAM) chip.

Answered by Shilpa Behl at 11:12 PM on April 26, 2008

Well Sujal,
Cache memory is usually on something like a hard drive or processor. It's a small amount of very high speed memory and the purpose is to put things that are accessed frequently into this very high speed memory so that you can get to them faster

RAM
Random Access Memory, a type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers.
There are two basic types of RAM:
dynamic RAM (DRAM)
static RAM (SRAM)
The two types differ in the technology they use to hold data, dynamic RAM being the more common type. Dynamic RAM needs to be refreshed thousands of times per second. Static RAM does not need to be refreshed, which makes it faster; but it is also more expensive than dynamic RAM. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off.

Answered by Bishan Preet at 11:02 PM on April 26, 2008

Memory is used in many different forms around modern PC systems, it can be divided into two essential types: RAM and ROM. ROM, or Read Only Memory, is relatively small, but essential to how a computer works. ROM is always found on motherboards, but is increasingly found on graphics cards and some other expansion cards and peripherals. Generally speaking, ROM does not change. It forms the basic instruction set for operating the hardware in the system, and the data within remains intact even when the computer is shut down. It is possible to update ROM, but it's only done rarely, and at need. If ROM is damaged, the computer system simply cannot function.
RAM, or Random Access Memory, is "volatile." This means that it only holds data while power is present. RAM changes constantly as the system operates, providing the storage for all data required by the operating system and software. Because of the demands made by increasingly powerful operating systems and software, system RAM requirements have accelerated dramatically over time. For instance, at the turn of the millennium a typical computer may have only 128Mb of RAM in total, but in 2007 computers commonly ship with 2Gb of RAM installed, and may include graphics cards with their own additional 512Mb of RAM and more.
cache memory----->
but since the 1990s "cache memory" has been employed as standard between the main memory and the processor. Not only this, CPU architecture has also evolved to include ever larger internal caches. The organisation of data this way is immensely complex, and the system uses ingenious electronic controls to ensure that the data the processor needs next is already in cache, physically closer to the processor and ready for fast retrieval and manipulation.
A small block of high-speed memory (usually SRAM) located between the CPU and main memory that is used to store frequently requested data and instructions. Properly designed, a cache improves system performance by reducing the need to access the system's slower main memory for every transaction.

Answered by jaivir at 8:36 PM on April 26, 2008

RAM stands for Random Access Memory, and it can contain programs, data, an operating system, pictures, videos, you name it. It's the main working area or scratchpad of your computer. It stays there until you turn the power off.
RAM is primary storage device. Its storage capacity is limited.It has a volatile memory. Two typw of RAM are available. Static RAM: No refreshing, 6 to 8 MOS transistors are required to form one memory cell, Information stored as voltage level in a flip flop. Dynamic RAM: Refreshed periodically, 3 to 4 transistors are required to form one memory cell, Information is stored as a charge in the gate to substrate capacitance.
Cache ram is very high-speed RAM chips which sit between the CPU and main memory. It stores (i.e., caches) memory accesses by the CPU. Cache ram helps to alleviate the gap between the speed of a CPU's megahertz rating and the ability of RAM to respond and deliver data. It reduces the frequency that the CPU must wait for data from the main memory.

Answered by Nagendra at 7:18 PM on April 26, 2008