Any computer, printer, or PDA will require memory to operate. You should have a basic understanding of what type of memory you require and how much you need. The memory we are speaking of here is referred to as "Random Access Memory" or RAM. Please don't confuse this with what is stored on your hard drive after you shut the power down on your computer. Once you shut your computer off, all Random Access Memory is gone. It's the memory that is actually residing in the computer itself when power is on and only when power is on. Any information that will be needed later will have to be stored or saved on some media such as a hard drive or floppy or or to some flash memory device. RAM, on the other hand resides in the computer and allows data to be accessed and manipulated quickly and in any order. The program you are running resides in RAM and at least some of the data at any given time may also reside in RAM. Your computer program is just a long list of instructions on what to do if this happens or if that happens and so on. Because of all these "what if" instructions, your program will know when it needs to go store something on the hard drive or go grab a piece of information from the hard drive. Imagine this.... The Computer & Program as being one secretary running around a large office with file cabinets lining the walls. Where as the computer gets instructions inputed from the keyboard or from the program its running, she receives her instructions over the phone or perhaps from over the counter or from what comes in today's mail. If a certain bill comes in, she walks over to one file and stores it. If a phone call come in and a customer wants to pay his bill, she goes to another file cabinet.

Now, just imagine..... the secretary is the computer and the file cabinets are the hard drive. To take it a step further, imagine the secretary was suddenly killed by a bolt of lightning! Horrible things like that do happen, but the fact is, what ever is stored in that file cabinet is still there. What ever was in that secretary's memory is gone forever. So now you should have a good understanding of the difference between RAM and your hard drive storage.

This may be a good time to explaine some very basic stuff regarding what a computer really is. As complex as it may seem, all information inside a computers and therefore in it's RAM memory is nothing more than a bunce of switches. Now imagine, each switch can only do or be one of two things. It can be on or it can be off. It's pretty hard to imagine anything as complex as a computer being based on such a simple principle, but now just imagine that there are two swhitches. With two switches, you have 4 different possibilities. Two on, Two off, Left switch on & right switch off, and visa versa. So far it's still pretty comprehensible. You could assign a value to each of the four possible combinations. 2 on might represent the letter "A" & 2 off might represent the letter "B". If you carry that out just a little further, the possibities become staggering! 8 on off switches can return

exponentially more possibilities than 2. 16 exponentially more than 8. 32 exponentially more than 16.

The stuff I'm talking about above is actually describes a term rarely heard any more; Machine Language. It also relates to terms you do still hear. Terms like 16 bit or 32 bit or 64 bit processors.

All of those on/off or ZERO/ONE switches are stored in your computers RAM memory. It is the processor that takes the data and then computes and manipulates the data as instructed by the operating system and the program you are running. No matter how powerful or fast the computer is, the information inside and the stuff you store on your hard drive at the end of the day is really nothing more than ones and zeros.

The on off switches are turned into ones and zeros and the guys that can deal with those one and zeros convert them into operation systems and somewhere down the line, people like us can type into a keyboard and actually do complicated task with nothing more than a bunch of switches.

Today's memory requirements are much different than they were in the early days of computing. Operating systems took up very little memory by today's standards. Most programs then were simply manipulating text and numbers. My first hard drive was a 5mb Corvus and I remember feeling like a superman and thinking to myself there was no way in the world I could ever fill up a 5mb hard drive. In the days of Windows 98, you may have gotten by fine with just 64mb of memory. Today we deal with hugh operating systems that are suited for the digital age and can manipulate digital sound and graphics which all consume huge amonts of memory. While you can still run Microsoft Windowx XP with128mb of memory, few would choose to do so. The minimum memory basically just accomodates the operating system and allows little room for programs or data that must also share that RAM memory. Basically, the more memory the better and faster your computer will perform. It means fewer trips to the file cabinet, fewer crashes and faster operations.

A Linux-based computer can get by with less memory than a typical Windows operating system. As little as 16MB of memory can successfully power a Linux system with a command line interface. As little as 64MB may be recommended for adding a graphical interface. Some Linux versions require more memory, such as Xandros (128MB) Linspire (128MB) or CentOS (256MB). Most of the types of memory listed below are available in two types. The standard size for Desktop computers and servers, and in the smaller size SODIMM (Small Outline) modules made for laptop computers. The SODIMMS are also designed to use less power to conserve battery use.

A SIMM (Single in-line memory module) was the first board that can could hold a group of memory chips instead of plugging in each chip individually as you did on early computer models like the Apple II. Instead, the SIMM board plugs into a SIMM socket on the motherboard. The first SIMMS had 30 pins and had an 8 bit wide bus. The 72 pin came out later and would hold up to eight or nine chips RAM memory chips and have a 32 bit wide bus. The ninth chip is used for parity error checking. Unlike memory chips, SIMMs were easier to install than individual chips. Unlike the DIMM which is used today, the contacts on a SIMM are redundant on both sides. Depending on the computer, SIMMs may be EDO or FPM and may need to be installed in pairs or groups of even groups of four. Usually EDO Memory will need to be installed in pairs. Fast page SIMMS can usually be installed individually. They may also be Parity (9 chips) or Non Parity (8 chips). SIMMS pop in place at an angle on the motherboard and have keyed knotches. These are still used to upgrade earlier computers, but are often costlier. You should weigh the cost vs investing in a new system which can be a better alternitive with the low cost of today's high performance systems and memory.

SDRAM, or Synchronous Dynamic Random Access Memory, is now a few generations old but is still be found in many computers. This type of memory is available in speeds of 66 MHz, 100 MHz, and 133 MHz (AKA PC66, PC100, and PC133). SDRAM for desktop computers features 168 pins for electrical/data transfer on a module measuring 5 1Ú4" long. SDRAM for notebook computers features 144 pins for electrical/data transfer on a module measuring about 2 5/8" long. SDRAM represented a big improvement in performance over previous generations of computer memory. The memory and processor were 'synchronized' and the data was available as needed. Later generations of computer memory like DDR and DDR-2, while increasing performance and speed, are built on the foundation laid by SDRAM.

DDR (Double Data Rate SDRAM) next generation and successor to SDRAM which is still used today. All current AMD-based systems utilize DDR memory, Most Intel-based systems now use the DDR-2.

DDR comes can transfer twice the data of an SDRAM module operating at the same speed. This is because DDR technology can send data on both the rise and the fall of a clock pulse. SDRAM can only sends data on the rise of a clock pulse.

Like RAMBUS, DDR uses its maximum theoretical bandwidth to describe the various speeds available. PC1600, PC2100, PC2700, and PC3200 are available. The bandwidth can be tied directly to a memory clock speed, with the following correlation:

.

DDR speeds are referenced by a DDR rate instead of the above straight clock speeds, so PC3200 would actually be called DDR400 or 400 MHz DDR.

Standards for memory are governed by a group called JEDEC (http://www.jedec.org), but manufacturers can design products outside of these specifications for computing enthusiasts. Non-standard memory (Usually DDR) are capable of much greater speeds with ratings as high as PC4000 or PC4400.

Desktop DDR memory uses 184 pins for electrical/data transfer on a module measuring about 5 1/4" long. DDR notebook memory uses 200 pins and measures about 2 5/8" in legnth. While DDR and SDRAM are the same size, the modules are keyed differently. SDRAM has 2 notches and DDR has only 1 notch in a different spot on the module so you can't accidently put in the wrong module.

DDR-2 memory for desktop computers has 240 pins and measures about 5 1/4" in legnth. DDR-2 for laptop computers uses 200 pins and measures roughly 2 5/8" in legnth. Just like DDR, DDR-2 is also keyed with one notch but at a different position than the standard DDR notch. This prevents installing the wrong memory.

DDR2 (Dual Data Rate Two) SDRAM, is the second generation of DDR memory and is now reaching the price/performance level to make it acceptable for mainstream computer systems. DDR2 nearly doubles the theoretical data transfer of DDR and still sends data on the rise and fall of the clock pulse. This is due to the increased number of memory buffers, lower power consumption, better thermal performance, and improved prefetch. Because most present DDR2 has higher latency within the memory, the actual performance improvement over standard DDR is only about 5%

A DDR-2 DIMM has a 64-bit wide data path or 72-bit for the ECC or registered DIMMS and because of that may br installed singly in 64-bit systems. If dual-channel memory is supported by the chipset, DDR2 has the effect of furnishing a 128-bit data path.

DDR2 memory now comes in three frequencies:

DDR-2 uses a similar naming structure to DDR, in that the maximum theoretical bandwidth is the typical method of describing a module. Instead of just a "PC" prefix, we now have a "PC2" to describe modules such as PC2-3200, PC2-4200, and PC2-5300. PC2-3200 has a DDR-2 speed of 400 MHz (4x100 MHz), PC2-4200 has a DDR-2 speed of 533 MHz (4x133 MHz), and PC2-5300 has a DDR-2 speed of 667 MHz (4x166 MHz). As with DDR (and others), overclocking memory is available in DDR-2, such as Corsair's DDR-2 PC2-8000, which operates at 1000 MHz!

DDR2 modules are not backward-compatible with DDR.

RIMM (Rambus Inline Memory Module), also known as Rambus or RDRAM, is a proprietary format launched by Rambus as a successor to SDRAM. Desktop RIMM modules feature 184 pins for electrical/data transfer on a module measuring roughly 5 1/4" long. The rating for RIMM memory is based on the maximum theoretical bandwidth (in MHz) and included speed ratings of 800 MHz, 1066 MHz, 1200 MHz, 1333 MHz, and 1600 MHz.

Many servers and systems using Intel Pentium 4 processors adopted the technology in the beginning, but DDR memory was launched at about the same time and eventually took almost all the market share. Some servers and even the the PlayStation II use RAMBUS memory.

The MICRO DIMM is a very tiny SO-DIMM with smaller diminsiona and thickness than the standard SO-DIMM. It was designed for extremely small and light weight Notebook computers and is used extensively on Sony Vaio laptops as well as Fujitsu and a few others. These are DDR2-400 and DDR2-533 modules and come in capacitys from 256mb up to 1 Gigabyte modules. They come in 172 pin and 214 pin configurations.

Memory is a key component of any computer system, and generally speaking, the more the better. At the very least, you need the appropriate amount of quality memory for the software and operating system you use. Just this can have a tremendous impact on a computers performance and reliability.