RAM is short for for Random Access Memory. The processor can process data very quickly, but if it can’t get that data quickly it doesn't matter how fast it works. The hard drive can hold lots of information, but its problem is in getting that information in and out. The hard drive moves slowly. That’s where RAM comes in. RAM can’t hold as much information as the hard drive, but it can transfer data very quickly. RAM is considered to be the resources which your computer uses for all of its computations. It's a temporary work area in which your computer uses, to do work.
RAM is the place where your programs reside while they're running and where your open files are stored before you hit the "save" command. If active programs and files take up more room than your RAM has available, your computer uses empty space on your hard drive to keep track of what's going on (called "paging to disk"). Hard drives have moving parts, which make them slower. RAM chips don't, which, in a general sense, is why having lots of RAM makes your computer run faster.
Memory works like a blackboard that is constantly overwritten with new data. The
amount of memory, or memory size, in a computer determines the number of programs you can run at once. Memory size also determines how fast your programs will operate. The data stored in memory is temporary. If you do not save the data, it will disappear when you turn off the computer.
RAM is also sometimes called read-write memory or RWM. This is actually a much more precise name, so of course it is hardly ever used. It's a better name because calling RAM "random access" implies to some people that ROM (discussed below) isn't random access, which is not true. RAM is called "random access" because earlier read-write did not allow random access. Sometimes old acronyms persist even when they don't make much sense anymore (e.g., the "AT" in the old IBM AT stands for "advanced technology”.
Obviously, RAM needs to be writable in order for it to do its job of holding programs and data that you are working on. The volatility of RAM also means that you risk losing what you are working on unless you save it frequently.
RAM is much faster than ROM is, due to the nature of how it stores information. If while surfing on The Web you notice that your hard drive light is constantly running or is blinking a good amount of the time, your computer is "going virtual" as we call it. This means that your machine is trying to run the programs by reading them off the hard drive then writing back to the hard drive and so forth. This kind of activity puts a lot of extra wear and tear on your hard drive; hence it shortens its life. Internet Explorer uses 8 meg of RAM and Windows 95 uses 8 meg of RAM why Mozilla Firefox uses 47 MB. therefore you need a minimum of 16 meg just to be on the Internet and more for Mozilla Firefox and so on.
This does not take into affect the amount of additional RAM your machine maybe using to load additional programs when your machine "boots up". More RAM (Random Access Memory) means a bigger work area for your machine to do its work and less work your hard drive has to do in order to keep up with your demands. RAM works at the speed of light and is therefor much
faster than trying to access the information using your hard drive. A hard drive uses mechanics in order to deliver the information you are requesting and it is therefor slower. It also has to go through more stuff before it is viewed by the user (you).
The more RAM you put into your machine the better it should run, quicker response times to your requests and most importantly of all, is the fact that it saves your hard drive from doing a lot of extra work, making it last longer. Keep in mind that it is your hard drive which is the device that holds All of the information you are and have been collecting, ... If that information is considered to be valuable to you, back it up. Make sure you back it up onto either a tape backup system, or the other solutions, just get it off the system for safe keeping!
Memory plays a significant role in the following important aspects of your computer system:
• Performance: The amount and type of system memory you have is an important contributing factor to overall performance. In many ways, it is more important than the processor, because insufficient memory can cause a processor to work at 50% or even more below its performance potential. This is an important point that is often overlooked.
• Software Support: Newer programs require more memory than old ones. More memory will give you access to programs that you cannot use with a lesser amount.
• Reliability and Stability: Bad memory is a leading cause of mysterious system problems. Having high-quality memory will result in a PC that runs smoothly and exhibits fewer problems. Also, even high-quality memory will not work well if you use the wrong kind.
• Upgradability: There are many different types of memory available, and some are more universal than others. Making a wise choice can allow you to migrate your memory it to a future system or continue to use it after you upgrade your motherboard.
SIMMs and DIMMs
RAM is kept on a circuit board. These circuit boards are either: SIMMs, an acronym for single inline memory module, which are small circuit boards that can hold a group of memory chips. Typically, SIMMs hold up 8 (on Macintosh's) or 9 (on PCs) RAM chips. On PCs, the ninth chip is often used for parity error checking 2. SIMMs are easier to install than individual memory chips. The bus from a SIMM to the actual memory chips is 32 bits wide. or DIMMs, short for dual in-line memory module, are small circuit boards that hold memory chips. A SIMM has a 32-bit path to the memory chips whereas a DIMM has 64-bit path. Because the Pentium processor requires a 64-bit path to 2 Parity checking refers to the use of numbers called parity bits to check that data has been transmitted accurately. The eight bits (zeros or ones) in a transmitted byte are added up prior to transmission. If the sum is odd, a 1 is added as the ninth bit. If the sum is even, the ninth bit is a zero. In post transmission the byte is again added together and its sum is checked with the parity bit. It the two do not confirm each other the data is ignored and resent. In this way parity checking is used to reduce errors. memory, you need to install SIMMs two at a time. With DIMMs, you can install memory one DIMM at a time.
A DIMM has 168 contacts and a SIMM has 72, so they're not interchangeable. Some computers use SIMMs, some use DIMMs, and some let you combine the two by providing both types of slots.
Different Types of RAM
There are many different types of RAMs, including static RAM (SRAM) and manyflavors of dynamic RAM (DRAM).
Dynamic RAM (DRAM)
When people refer to their RAM, they usually mean Dynamic RAM, which is a type of RAM that only holds its data if it is continuously accessed by special part called a refresh circuit. Many hundreds of times each second, this circuitry reads the contents of each memory cell, whether the memory cell is being used at that time by the computer or not. Due to the way in which the cells are constructed, the reading action itself refreshes the contents of the memory. If this is not done
regularly, then the DRAM will lose its contents, even if it continues to have power supplied to it. This refreshing action is why the memory is called dynamic.
All PCs use DRAM for their main system memory, instead of SRAM, even though DRAMs are slower than SRAMs and require the overhead of the refresh circuitry. It may seem weird to want to make the computer's memory out of something that can only hold a value for a fraction of a second. In fact, DRAMs are both more complicated and slower than SRAMs. The reason that DRAMs are used is simple: they are much cheaper and take up much less space, typically 1/4 the silicon area of SRAMs or less. To build a 64 MB core memory from SRAMs would be very expensive. The overhead of the refresh circuit is tolerated in order to allow the use of large amounts of inexpensive, compact memory. The refresh circuitry itself is almost never a
problem; many years of using DRAM has caused the design of these circuits to be all but perfected.
DRAMs are smaller and less expensive than SRAMs because SRAMs are made from four to six transistors (or more) per bit, DRAMs use only one, plus a capacitor. The capacitor, when energized, holds an electrical charge if the bit contains a "1" or no charge if it contains a "0". The transistor is used to read the contents of the capacitor. The problem with capacitors is that they only hold a charge for a short period of time, and then it fades away. These capacitors are
tiny, so their charges fade particularly quickly. This is why the refresh circuitry is needed: to read the contents of every cell and refresh them with a fresh "charge" before the contents fade away and are lost. Refreshing is done by reading every "row" in the memory chip one row at a time; the process of reading the contents of each capacitor re-establishes the charge.
DRAM is manufactured using a similar process to how processors are: a silicon substrate is etched with the patterns that make the transistors and capacitors (and support structures) that comprise each bit. DRAM costs much less than a processor because it is a series of simple, repeated structures, so there isn't the complexity of making a single chip with several million individually located transistors.
There are many different kinds of specific DRAM technologies and speeds that they are available in. These have evolved over many years of using DRAM for
system memory.
Static RAM (SRAM)
Static RAM is a type of RAM that holds its data without external refresh, for as long as power is supplied to the circuit. This is contrasted to dynamic RAM (DRAM), which must be refreshed many times per second in order to hold its data contents. SRAMs are used for specific applications within the PC, where their strengths outweigh their weaknesses compared to DRAM:
• Simplicity: SRAMs don't require external refresh circuitry or other work in
order for them to keep their data intact.
• Speed: SRAM is faster than DRAM.
In contrast, SRAMs have the following weaknesses, compared to DRAMs:
• Cost: SRAM is, byte for byte, several times more expensive than DRAM.
• Size: SRAMs take up much more space than DRAMs (which is part of why the cost is higher).
These advantages and disadvantages taken together obviously show that performance-wise, SRAM is superior to DRAM, and we would use it exclusively if only we could do so economically. Unfortunately, 32 MB of SRAM would be prohibitively large and costly, which is why DRAM is used for system memory. SRAMs are used instead for special kinds of memory called level 1 cache and level 2 cache memory (discussed below), for which it is perfectly suited; cache
memory needs to be very fast, and not very large.
SRAM is manufactured in a way rather similar to how processors are: highly integrated transistor patterns photo-etched into silicon. Each SRAM bit is comprised of between four and six transistors, which is why SRAM takes up much more space compared to DRAM, which uses only one (plus a capacitor). Because an SRAM chip is comprised of thousands or millions of identical cells, it is much easier to make than a CPU, which is a large die with a non-repetitive
structure. This is one reason why RAM chips cost much less than processors do.
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