The most important thing to ensure when buying memory is compatibility with your system. In addition, you will need to decide how much memory you need and beyond that lie considerations of price, quality, availability, service, and warranty. This section helps you address these important decision factors and helps you answer questions like these:
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- How much memory do you need?
- How much memory will your system recognize?
- What kind of memory is compatible with your system?
- How many sockets are open and how should you fill them?
- How do you determine the quality of memory?
- What should you know about memory prices?
- What other issues should you consider?
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Compatibility of memory components with your computer system is arguably the most important factor to consider when upgrading memory. This section can get you started.
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The easiest way to determine what type of memory goes with your system is to consult with your system documentation. In most cases, the manual will provide basic specifications such as the speed and technology of the memory you need. This information is usually enough to choose a module by specification. If you do not feel you have enough information, you can call your system manufacturer's toll-free technical support number for assistance.
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You may or may not have an idea what the inside of your computer looks like and how memory is configured. You may have opened up your computer when you bought it to see the configuration inside, or you may have looked at a configuration diagram in your user's manual. Even if you have no idea of the memory configuration of your system, you can use Kingston's memory configuration tools to find out. For each system, the configuration includes a diagram, which indicates how the memory sockets are arranged in your system and what the basic configuration rules are.
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Non-removable memory usually comes in the form of memory chips soldered directly onto the system board. It is represented in the bank schema in brackets: [_4MB_] indicates 4MB of non-removable memory soldered onto the board and two available memory sockets.
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You can find out how many sockets are in the system and how many are filled by pressing the F1 key during system startup. If your system supports this, a screen will appear that indicates how many memory sockets are in the system, which ones are filled and which are open, and what capacity modules are in each socket. If pressing the F1 key during startup does not produce this result, check your computer's system manual for more information.
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Try reseating the DIMM. Make sure the DIMM notches are correctly lined up with the notches in the socket. Then, push straight down on the DIMM; make sure you push down with a reasonable amount of force (wrist strength not shoulder power). Often people are afraid to push down hard enough and the DIMM doesn't make full contact with the leads in the socket. It is important that the metal leads on the DIMM almost disappear into the socket.
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As a last resort, you can open your computer and look at the sockets. (Important Note: Before removing the cover of your computer, refer to the computer's system manual and warranty information for instructions and other relevant information.) If you do open the computer, you may be able to identify "bank labels" that indicate whether memory are installed in pairs. Bank numbering typically begins with 0 instead of 1. Therefore, if you have two banks, the first bank will be labeled "bank 0", and the second bank will be labeled "bank 1."
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In most cases, it is best to plan your memory upgrade so you will not have to remove and discard the memory that came with the computer. The best way to manage this is to consider the memory configuration when you first buy the computer. Because lower-capacity modules are less expensive and more readily available, system manufacturers may achieve a base configuration by filling more sockets with lower-capacity modules. By way of illustration, consider this scenario: a computer system with 64MB standard memory comes with either two (2) 32MB modules or one (1) 64MB module. In this case, the second configuration is the better choice because it leaves more room for growth and reduces the chance that you will have to remove and discard lower-capacity modules later. Unless you insist on the (1) 64MB module configuration, you may find yourself with only one socket left open for upgrading later.
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You may or may not have an idea what the inside of your computer looks like and how memory is configured. You may have opened up your computer when you bought it to see the configuration inside, or you may have looked at a configuration diagram in your user's manual. Even if you have no idea of the memory configuration of your system, you can use Kingston's memory configuration tools to find out. For each system, the configuration includes a diagram, which indicates how the memory sockets are arranged in your system and what the basic configuration rules are
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Non-removable memory usually comes in the form of memory chips soldered directly onto the system board. It is represented in the bank schema in brackets: [_4MB_] indicates 4MB of non-removable memory soldered onto the board and two available memory sockets. Non-removable memory usually comes in the form of memory chips soldered directly onto the system board. It is represented in the bank schema in brackets: [_4MB_] indicates 4MB of non-removable memory soldered onto the board and two available memory sockets.
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You can find out how many sockets are in the system and how many are filled by pressing the F1 key during system startup. If your system supports this, a screen will appear that indicates how many memory sockets are in the system, which ones are filled and which are open, and what capacity modules are in each socket. If pressing the F1 key during startup does not produce this result, check your computer's system manual for more information
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As a last resort, you can open your computer and look at the sockets. (Important Note: Before removing the cover of your computer, refer to the computer's system manual and warranty information for instructions and other relevant information.) If you do open the computer, you may be able to identify "bank labels" that indicate whether memory are installed in pairs. Bank numbering typically begins with 0 instead of 1. Therefore, if you have two banks, the first bank will be labeled "bank 0", and the second bank will be labeled "bank 1."
TOP PAGE

In most cases, it is best to plan your memory upgrade so you will not have to remove and discard the memory that came with the computer. The best way to manage this is to consider the memory configuration when you first buy the computer. Because lower-capacity modules are less expensive and more readily available, system manufacturers may achieve a base configuration by filling more sockets with lower-capacity modules. By way of illustration, consider this scenario: a computer system with 64MB standard memory comes with either two (2) 32MB modules or one (1) 64MB module. In this case, the second configuration is the better choice because it leaves more room for growth and reduces the chance that you will have to remove and discard lower-capacity modules later. Unless you insist on the (1) 64MB module configuration, you may find yourself with only one socket left open for upgrading later.
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Once you have purchased a computer and are planning your first upgrade, plan to buy the highest-capacity module you think you may need, especially if you only have one or two sockets available for upgrading. Keep in mind that, in general, minimum memory requirements for software applications double every 12 to 18 months, so a memory configuration that's considered large today will seem much less so a year from now.
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Some people like to know a lot about the computer systems they own - or are considering buying - just because. They are like that. It is what makes them tick. Some people never find out about their systems and like it that way. Still other people - most of us, in fact - find out about their systems when they have to - when something goes wrong, or when they want to upgrade it. It is important to note that making a choice about a computer system - and its memory features - will affect the experience and satisfaction you derive from the system. This chapter is here to make you smarter about memory so that you can get more out of the system you are purchasing or upgrading.
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The easiest way to categorize memory is by form factor. The form factor of any memory module describes its size and pin configuration. Most computer systems have memory sockets that can accept only one form factor. Some computer systems are designed with more than one type of memory socket, allowing a choice between two or more form factors. Such designs are usually a result of transitional periods in the industry when it is not clear which form factors will gain predominance or be more available.
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As previously mentioned, the term SIMM stands for Single In-Line Memory Module. With SIMMs, memory chips are soldered onto a modular printed circuit board (PCB), which inserts into a socket on the system board.
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The first SIMMs transferred 8 bits of data at a time. Later, as CPUs began to read data in 32-bit chunks, a wider SIMM was developed, which could supply 32 bits of data at a time. The easiest way to differentiate between these two different kinds of SIMMs was by the number of pins, or connectors. The earlier modules had 30 pins and the later modules had 72 pins. Thus, they became commonly referred to as 30-pin SIMMs and 72-pin SIMMs.
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Another important difference between 30-pin and 72-pin SIMMs is that 72-pin SIMMs are 3/4 of an inch (about 1.9 centimeters) longer than the 30-pin SIMMs and have a notch in the lower middle of the PCB. The graphic below compares the two types of SIMMs and indicates their data widths.
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Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
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168-pin DIMMs transfer 64 bits of data at a time and are typically used in computer configurations that support a 64-bit or wider memory bus. Some of the physical differences between 168-pin DIMMs and 72-pin SIMMs include the length of module, the number of notches on the module, and the way the module installs in the socket. Another difference is that many 72-pin SIMMs install at a slight angle, whereas 168-pin DIMMs install straight into the memory socket and remain completely vertical in relation to the system motherboard. The illustration below compares a 168-pin DIMM to a 72-pin SIMM.
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A type of memory commonly used in notebook computers is called SO DIMM or Small Outline DIMM. The principal difference between a SO DIMM and a DIMM is that the SO DIMM, because it is intended for use in notebook computers, is significantly smaller than the standard DIMM. The 72-pin SO DIMM is 32 bits wide and the 144-pin SO DIMM is 64 bits wide.
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RIMM is the trademarked name for a Direct Rambus memory module. RIMMs look similar to DIMMs, but have a different pin count. RIMMs transfer data in 16-bit chunks. The faster access and transfer speed generates more heat. An aluminum sheath, called a heat spreader, covers the module to protect the chips from overheating.
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Flash memory is a solid-state, non-volatile, rewritable memory that functions like RAM and a hard disk drive combined. Flash memory stores bits of electronic data in memory cells, just like DRAM, but it also works like a hard-disk drive in that when the power is turned off, the data remains in memory. Because of its high speed, durability, and low voltage requirements, flash memory is ideal for use in many applications - such as digital cameras, cell phones, printers, handheld computers, pagers, and audio recorders.
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Before SO DIMMs became popular, most notebook memory was developed using proprietary designs. It is always more cost-effective for a system manufacturer to use standard components, and at one point, it became popular to use the same "credit card" like packaging for memory that is used on PC Cards today. Because the modules looked like PC Cards, many people thought the memory cards were the same as PC Cards, and could fit into PC Card slots. At the time, this memory was described as "Credit Card Memory" because the form factor was the approximate size of a credit card. Because of its compact form factor, credit card memory was ideal for notebook applications where space is limited.
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MAJOR CHIP TECHNOLOGIES
It is usually pretty easy to tell memory module form factors apart because of physical differences. Most module form factors can support various memory technologies so, it is possible for two modules to appear to be the same when, in fact, they're not. For example, a 168-pin DIMM can be used for EDO, Synchronous DRAM, or some other type of memory. The only way to tell precisely what kind of memory a module contains is to interpret the marking on the chips. Each DRAM chip manufacturer has different markings and part numbers to identify the chip technology.
FAST PAGE MODE (FPM)
At one time, FPM was the most common form of DRAM found in computers. In fact, it was so common that people simply called it "DRAM," leaving off the "FPM". FPM offered an advantage over earlier memory technologies because it enabled faster access to data located within the same row.
EXTENDED DATA OUT (EDO)
In 1995, EDO became the next memory innovation. It was similar to FPM, but with a slight modification that allowed consecutive memory accesses to occur much faster. This meant the memory controller could save time by cutting out a few steps in the addressing process. EDO enabled the CPU to access memory 10 to 15% faster than with FPM.
SYNCHRONOUS DRAM (SDRAM)
In late 1996, SDRAM began to appear in systems. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM chips also take advantage of interleaving and burst mode functions, which make memory retrieval even faster. SDRAM modules come in several different speeds to synchronize to the clock speeds of the systems they will be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such as 200MHz and 266MHz are currently in development.
DOUBLE DATA RATE SYNCHRONOUS DRAM (DDR SDRAM)
DDR SDRAM, is a next-generation SDRAM technology. It allows the memory chip to perform transactions on both the rising and falling edges of the clock cycle. For example, with DDR SDRAM, a 100 or 133MHz memory bus clock rate yields an effective data rate of 200MHz or 266MHz. Systems using DDR SDRAM are expected to ship at the end of the year 2000.
DIRECT RAMBUS
Direct Rambus is a new DRAM architecture and interface standard that challenges traditional main memory designs. Direct Rambus technology is extraordinarily fast compared to older memory technologies. It transfers data at speeds up to 800MHz over a narrow 16-bit bus called a Direct Rambus Channel. This high-speed clock rate is possible due to a feature called "double clocked," which allows operations to occur on both the rising and falling edges of the clock cycle. In addition, each memory device on an RDRAM module provides up to 1.6 gigabytes per second of bandwidth - twice the bandwidth available with current 100MHz SDRAM.
In addition to chip technologies designed for use in main memory, there are also specialty memory technologies that have been developed for video applications.
MAJOR CHIP TECHNOLOGIES
It is usually pretty easy to tell memory module form factors apart because of physical differences. Most module form factors can support various memory technologies so, it is possible for two modules to appear to be the same when, in fact, they're not. For example, a 168-pin DIMM can be used for EDO, Synchronous DRAM, or some other type of memory. The only way to tell precisely what kind of memory a module contains is to interpret the marking on the chips. Each DRAM chip manufacturer has different markings and part numbers to identify the chip technology.
FAST PAGE MODE (FPM)
At one time, FPM was the most common form of DRAM found in computers. In fact, it was so common that people simply called it "DRAM," leaving off the "FPM". FPM offered an advantage over earlier memory technologies because it enabled faster access to data located within the same row.
EXTENDED DATA OUT (EDO)
In 1995, EDO became the next memory innovation. It was similar to FPM, but with a slight modification that allowed consecutive memory accesses to occur much faster. This meant the memory controller could save time by cutting out a few steps in the addressing process. EDO enabled the CPU to access memory 10 to 15% faster than with FPM.
SYNCHRONOUS DRAM (SDRAM)
In late 1996, SDRAM began to appear in systems. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM chips also take advantage of interleaving and burst mode functions, which make memory retrieval even faster. SDRAM modules come in several different speeds to synchronize to the clock speeds of the systems they will be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such as 200MHz and 266MHz are currently in development.
DOUBLE DATA RATE SYNCHRONOUS DRAM (DDR SDRAM)
DDR SDRAM, is a next-generation SDRAM technology. It allows the memory chip to perform transactions on both the rising and falling edges of the clock cycle. For example, with DDR SDRAM, a 100 or 133MHz memory bus clock rate yields an effective data rate of 200MHz or 266MHz. Systems using DDR SDRAM are expected to ship at the end of the year 2000.
DIRECT RAMBUS
Direct Rambus is a new DRAM architecture and interface standard that challenges traditional main memory designs. Direct Rambus technology is extraordinarily fast compared to older memory technologies. It transfers data at speeds up to 800MHz over a narrow 16-bit bus called a Direct Rambus Channel. This high-speed clock rate is possible due to a feature called "double clocked," which allows operations to occur on both the rising and falling edges of the clock cycle. In addition, each memory device on an RDRAM module provides up to 1.6 gigabytes per second of bandwidth - twice the bandwidth available with current 100MHz SDRAM.
In addition to chip technologies designed for use in main memory, there are also specialty memory technologies that have been developed for video applications.
SYNCHRONOUS DRAM (SDRAM) In late 1996, SDRAM began to appear in systems. Unlike previous technologies, SDRAM is designed to synchronize itself with the timing of the CPU. This enables the memory controller to know the exact clock cycle when the requested data will be ready, so the CPU no longer has to wait between memory accesses. SDRAM chips also take advantage of interleaving and burst mode functions, which make memory retrieval even faster. SDRAM modules come in several different speeds to synchronize to the clock speeds of the systems they will be used in. For example, PC66 SDRAM runs at 66MHz, PC100 SDRAM runs at 100MHz, PC133 SDRAM runs at 133MHz, and so on. Faster SDRAM speeds such as 200MHz and 266MHz are currently in development. DOUBLE DATA RATE SYNCHRONOUS DRAM (DDR SDRAM) DDR SDRAM, is a next-generation SDRAM technology. It allows the memory chip to perform transactions on both the rising and falling edges of the clock cycle. For example, with DDR SDRAM, a 100 or 133MHz memory bus clock rate yields an effective data rate of 200MHz or 266MHz. Systems using DDR SDRAM are expected to ship at the end of the year 2000. DIRECT RAMBUS Direct Rambus is a new DRAM architecture and interface standard that challenges traditional main memory designs. Direct Rambus technology is extraordinarily fast compared to older memory technologies. It transfers data at speeds up to 800MHz over a narrow 16-bit bus called a Direct Rambus Channel. This high-speed clock rate is possible due to a feature called "double clocked," which allows operations to occur on both the rising and falling edges of the clock cycle. In addition, each memory device on an RDRAM module provides up to 1.6 gigabytes per second of bandwidth - twice the bandwidth available with current 100MHz SDRAM. In addition to chip technologies designed for use in main memory, there are also specialty memory technologies that have been developed for video applications. MEMORY TECHNOLOGIES FOR VIDEO OR GRAPHICS PROCESSING VIDEO RAM (VRAM) VRAM is a video version of FPM technology. VRAM typically has two ports instead of one, which allows the memory to allocate one channel to refreshing the screen while the other is focused on changing the images on the screen. This works much more efficiently than regular DRAM when it comes to video applications. However, since video memory chips are used in much lower quantities than main memory chips, they tend to be more expensive. Therefore, a system designer may choose to use regular DRAM in a video subsystem, depending on whether cost or performance is the design objective. WINDOW RAM (WRAM) WRAM is another type of dual-ported memory also used in graphics-intensive systems. It differs slightly from VRAM in that its dedicated display port is smaller and it supports EDO features. SYNCHRONOUS GRAPHICS RAM (SGRAM) SGRAM is a video-specific extension of SDRAM that includes graphics-specific read/write features. SGRAM also allows data to be retrieved and modified in blocks, instead of individually. This reduces the number of reads and writes that memory must perform and increases the performance of the graphics controller by making the process more efficient. BASE RAMBUS AND CONCURRENT RAMBUS Before it even became a contender for main memory, Rambus technology was actually used in video memory. The current Rambus main memory technology is called Direct Rambus. Two earlier forms of Rambus are Base Rambus and Concurrent Rambus. These forms of Rambus have been used in specialty video applications in some workstations and video game systems like Nintendo 64 for several years. HOW MUCH MEMORY DO YOU NEED? Perhaps you already know what it is like to work on a computer that does not have quite enough memory. You can hear the hard drive operating more frequently and the "hour glass" or "wrist watch" cursor symbol appears on the screen for longer periods. Things can run more slowly at times, memory errors can occur more frequently, and sometimes you cannot launch an application or a file without first closing or quitting another. So, how do you determine if you have enough memory, or if you would benefit from more? In addition, if you do need more, how much more? The fact is, the right amount of memory depends on the type of system you have, the type of work you are doing, and the software applications you are using. Because the right amount of memory is likely to be different for a desktop computer than for a server, we have divided this section into two parts - one for each type of system. MEMORY REQUIREMENTS FOR A DESKTOP COMPUTER If you are using a desktop computer, memory requirements depend on the computer's operating system and the application software you are using. Today's word processing and spreadsheet applications require as little as 32MB of memory to run. However, software and operating system developers continue to extend the capabilities of their products, which usually mean greater memory requirements. Today, developers typically assume a minimum memory configuration of 64MB. Systems used for graphic arts, publishing, and multimedia call for at least 128MB of memory and it's common for such systems to require 256MB or more for best performance. INSTALLING MEMORY Before you start, make sure you have the following: Your computer manual. To install memory, you must open the computer box (chassis) and locate the memory sockets. You may need to unplug cables and peripherals, and re-install them afterward. The manual will most likely provide instructions specific to your computer. A small screwdriver. Most computer chassis assemble with screws. The screwdriver also comes in handy if the notches on memory sockets are too tiny for your fingers. IMPORTANT THINGS TO KEEP IN MIND ESD DAMAGE Electro-Static Discharge (ESD) is a frequent cause of damage to the memory module. ESD is the result of handling the module without first properly grounding yourself and thereby dissipating static electricity from your body or clothing. If you have a grounded wrist strap, wear it. If you do not, before touching electronic components - especially your new memory module - make sure you first touch an unpainted, grounded metal object. Most convenient is the metal frame inside the computer. In addition, always handle the module by the edges. If ESD damages memory, problems may not show up immediately and may be difficult to diagnose. Wearing a grounded wrist strap can prevent ESD damage. SWITCHING OFF THE POWER Before opening the chassis, always power-off your computer and all attached peripherals. Leaving power on can cause permanent electrical damage to your computer and its components. INSTALLING THE MEMORY The vast majority of computers today have memory sockets that accept the following industry-standard memory modules: Desktops, Workstations and Servers 72-pin SIMM 168-pin DIMM 184-pin RIMM Notebooks and Mobile Computers 144-pin SO DIMM Although sockets may be in different places on different computers, installation is the same. Consult the computer owner's manual to find out whether the memory sits on an expansion card or on the motherboard, and whether internal computer components must be moved to gain access. In the section below are installation instructions for the standard modules listed above, followed by installation instructions for some of the more popular proprietary memory modules. If the computer requires proprietary memory, or the instructions below do not seem to apply to your situation, phone Kingston Technology's Technical Support Group at (800) 435-0640. INSTALLING A 72-PIN SIMM Place your computer's power switch in the off position and disconnect the AC power cord. Follow the instructions in your owner's manual that describe how to locate your computer's memory expansion sockets. Before touching any electronic components or opening the package containing your new module(s), make sure you first touch an unpainted, grounded metal object to discharge any static electricity you may have stored on your body or clothing. Handle your new module(s) carefully; do not flex or bend the module(s). Always grasp the module by its edges. As shown in the illustration, the module and the expansion socket are keyed. A small plastic bridge in the socket must align with the curved notch in the module. The bridge ensures the module can only be plugged into the socket one way. Insert the module into the socket at a slight angle. Make sure the module is completely seated in the socket. If you're having problems inserting the module into the socket, stop and examine both the module and the socket; make sure the notch in the module is properly aligned with the keyed plastic bridge in the socket. Do not force the module into the socket. If too much force is used, both the socket and module could be damaged. Once you are satisfied the module is seated properly in the socket, rotate the module upward until the clips at each end of the expansion socket click into place. After all modules have been installed, close the computer, plug in the AC power cord, and reinstall any other cables that may have been disconnected during the installation process. INSTALLING A 168-PIN DIMM Locate the memory expansion sockets on the computer's motherboard. If all the sockets are full, you will need to remove smaller capacity modules to allow room for higher capacity modules. For some installations, DIMM memory can be installed in any available expansion slot. Other installations may require the memory to be installed in a particular sequence based on the module's capacity. Check your owner's manual to determine the correct installation sequence for your configuration. Insert the module into an available expansion socket as shown in the illustration. Note how the module is keyed to the socket. This ensures the module can be plugged into the socket one way only. Firmly press the module into position, making certain the module is completely seated in the socket. Repeat this procedure for any additional modules you are installing. Most 168-pin DIMM modules have ejector tabs similar to those shown in the illustration. The ejector tabs are used only when you need to remove a module. By pressing down on the ejector tabs, the module will pop up from the socket and it can be removed. INSTALLING A 184-PIN RIMM Turn off the computer and disconnect the AC power cord. Locate your computer's memory expansion sockets by following the instructions in your owner's manual. Before touching any electronic components, make sure you first touch an unpainted, grounded metal object to discharge any static electricity stored on your clothing or body. If all the sockets are full, you will need to remove smaller capacity modules to allow room for higher capacity modules. The ejector tabs shown in the illustration are used to remove a module. By pushing outward on the ejector tabs, the module will pop up from the socket and it can then be removed. For most installations, Rambus modules can be installed in any available expansion socket, but any empty sockets must contain a continuity module as shown in the illustration. Note that some modes may use a specific installation sequence for Rambus modules (e.g. Rambus dual-channel configurations); see your owner's manual for more details. Insert the module into an available expansion socket as shown in the illustration. Note how the module is keyed to the socket. This ensures the module can be plugged into the socket one way only. Firmly press the module into position, making certain the module is completely seated in the socket. The ejector tabs at each end of the socket will automatically snap into the locked position. Repeat this procedure for any additional modules are installing. Once the module or modules have been installed, close the computer.
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Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
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Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
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Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
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Dual In-line Memory Modules, or DIMMs, closely resemble SIMMs. Like SIMMs, most DIMMs install vertically into expansion sockets. The principal difference between the two is that on a SIMM, pins on opposite sides of the board are "tied together" to form one electrical contact; on a DIMM, opposing pins remain electrically isolated to form two separate contacts.
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