Finding out how much memory a computer has is one popular way to measure that computer’s power and capabilities. Think about it: If someone asked you what kind of computer you have, what would you answer? Probably something like, “I have an Intel i7 Processor with 16 gigs of RAM.” But why do we measure the power of a computer based on the amount of memory it has?
In this chapter, you discover the purpose of memory and some of the different types of memory found in computers today. This chapter also discusses issues that affect installing memory in personal computers and laptops.
Understanding the Types of Memory
This section outlines different types of computer memory — anything that stores information either permanently or temporarily. Computers have two different flavors of memory: ROM and RAM.
Make sure you fully understand the different types of memory and their uses. You are sure to see a few questions on memory.
Remembering the purpose of memory
Before you look at the different types of memory, you need to understand the purpose of memory. Think about your desk at home or in the office. Whether sitting at your home or office desk (working on a proposal or preparing for your A+ Exams), chances are good that your desk is covered with documents, books, and papers. This desk is your work area, and its size dictates how many documents you can work on at any given time.
System memory works the same way. You have documents and applications stored on the hard drive. When you want to work on these documents, you open them and place them in the computer’s work area. The work area (or desk space) for a computer is system memory. When you want to work with any application or document, the computer must retrieve that information from the hard drive and execute it from memory.
Assume, for instance, that your computer has 4GB of memory. You start up your system, which is running Windows 8.1, and decide to run Microsoft Word and Adobe Photoshop at the same time. Assume that you open two very large files in each application. Assume further that you are using 3GB of precious memory at this point — for the operating system (OS) to load, and memory for each running application. As you can see, your memory usage adds up quickly.
In this scenario, you are already using 3GB of memory, which leaves a scant 1GB of memory remaining. Assume that you are about to open a Photoshop document and copy and paste information from one file to another. To put it simply, you are running out of desk space. You can solve the problem in one of two ways:
Do less work. In other words, work in one application at a time. This is not an optimal solution, especially for business users who often need to run multiple applications simultaneously.
Get a bigger desk. In computer terminology, install more RAM. When you install more RAM, you have a bigger desk to work on.
Now that you understand the general purpose of memory, it’s time to dive into the different types of memory. For the A+ Exams, you are required to know many different types of memory, which I outline in the following sections.
Read-only memory (ROM)
ROM is a type of memory that you cannot write to: hence its name, read-only memory. Information is written to ROM chips by the manufacturer, and this information cannot be changed. In the past, if ROM information needed to be updated, you had to remove the original ROM chip and replace it with an updated ROM chip from the manufacturer. Today, you can update the ROM by running a special software program downloaded from the manufacturer’s website. In essence, you do not really have a ROM chip but rather have an EEPROM (more on EEPROM in a bit).
Software written to a ROM chip is firmware.
One of the major uses for ROM is storing the system BIOS (basic input-output system), which contains the Power-on Self-Test (POST) routines and other routines that initiate loading the OS. The BIOS also contains the low-level code that allows the system to communicate with hardware devices.
You need to know that the POST is part of the BIOS code stored in ROM. The POST contains routines that initiate OS loading as well as routines that make communication between hardware devices possible.
EPROM
EPROM (erasable programmable ROM) is a type of memory that normally cannot be written to because it is a variation of ROM. An EPROM chip is a special ROM chip that the manufacturer can reprogram by using a special programming device that uses ultraviolet light.
EEPROM
A newer implementation of ROM is electrically erasable programmable ROM (EEPROM), or flash ROM. The manufacturer writes the software instructions into the ROM chip, but you can update these instructions by running a special software setup program provided by the manufacturer. The software setup program is usually available through the manufacturer’s website.
EEPROM (better known as flash ROM) is a ROM chip that can be rewritten with special EEPROM update software provided by the manufacturer of the chip.
Using EEPROM has become the typical way to update your BIOS. BIOS code is designed to work with certain hardware. As hardware improves, you need to update your BIOS code so that your system is aware of these hardware improvements. Therefore, the manufacturer places BIOS updates on its website to download for computer users running its particular BIOS. You just have to download the BIOS update program and then run the BIOS update on your system. The update rewrites the BIOS instructions, making the computer “more aware” of today’s hardware.
Some examples where you will need to download a BIOS update from a manufacturer’s website is if you want to update the capabilities (the BIOS) of your computer or your home router. In these scenarios, you navigate to the manufacturer’s website and download the firmware (BIOS) update and then run it on your computer or supply the update into the administration pages of the home router.
Random access memory (RAM)
Of the two flavors of memory (ROM and RAM), RAM is probably the more fundamental. As I mention earlier, ROM is permanent memory, or permanent storage of information. As the computer’s primary working memory, though, RAM stores information temporarily. RAM is volatile, meaning that it needs constant electrical current to maintain the information that resides in its chips. If the electrical current is lost, RAM contents are erased. Likewise, when a computer is powered off, all RAM contents are flushed out. The following sections discuss the different types of RAM.
You can expect a few questions about the different types of memory. Be sure that you are familiar with these different types of RAM.
DRAM
Dynamic RAM (DRAM) is probably the most popular type of memory today and the one that you are most often going to upgrade. When someone says to you, “I have 1024 megs of dynamic RAM,” he or she is talking about DRAM.
Dynamic RAM gets its name from the fact that the information stored in DRAM needs to be constantly refreshed. Refreshing involves reading the bits of data stored in DRAM and then rewriting the same information back.
DRAM is single-ported: You can read and write to the memory but not at the same time.
Older implementations of RAM measured the memory’s performance based on how long it took the CPU to access that data. This time is measured in nanoseconds (ns; 1 ns equals one-billionth of a second). If you have memory that is 50 ns and your best friend has memory that is 70 ns, your memory is presumably faster. Your CPU receives the information from memory after waiting only 50-billionths of a second, whereas your best friend’s CPU waits 70-billionths of a second.
The lower the number of nanoseconds, the better the performance.
The speed of older DRAM ranges from 60 ns to 80 ns. Today’s implementations of DRAM measure the speed of memory in megahertz (MHz), typically matching the motherboard speed. For example, my Intel i7 computer has memory that is running at 800 MHz.
Static RAM (SRAM) — so-called because the information held in its memory cells doesn’t need to be refreshed — requires less overhead than DRAM to maintain the information stored in memory.
With speeds running from 10 ns to 20 ns, SRAM is much faster than DRAM. Because SRAM is faster memory than DRAM, it is also more expensive, which is why people add DRAM to their systems more often than they add SRAM.
SRAM is typically used for cache memory, which stores frequently used data and program code after it is read from slower DRAM. Think of cache memory as a bucket that sits beside the CPU and stores frequently used information. After the system has searched through DRAM once for specific information, it can store that information in the bucket for easy access later. The next time the data is requested, it is read from cache instead of from system memory.
Because cache memory is much faster than DRAM, the CPU first tries to retrieve the information from cache: specifically, L1 cache first and then L2 cache. If the information is not located in cache, the system then tries to retrieve the information from memory. If the information is not located in system memory, it then is retrieved from disk. Attempting to retrieve the requested information from cache first reduces wait time if the information actually resides there because of how fast cache is compared with DRAM.
Cache memory (SRAM) stores frequently used data and program code. Because cache memory is faster than DRAM, retrieving information from cache means that the processor does not have to wait for the slower DRAM, thus enhancing system performance.
CMOS RAM
The complementary metal-oxide semiconductor (CMOS) is the area where the computer stores its configuration information, such as whether the computer has a floppy drive, the amount of memory installed, the date and time for the system, and the number and size of the hard drives that are installed. Think of CMOS information as an inventory list for the majority of components that are installed on the computer. For more information on CMOS, see Book 2, Chapter 4.
Where is CMOS information stored? Is CMOS information stored on the BIOS chip, or perhaps another ROM chip? The answer is neither. In fact, if the information were stored on a ROM chip, you wouldn’t be able to go into the CMOS setup program and change the configuration. Instead, CMOS configuration information is stored in a type of RAM called CMOS RAM.
CMOS RAM is a special, volatile RAM chip that stores the CMOS information. If power is lost, the information is wiped out. This could present a problem with regard to CMOS configuration because if CMOS RAM is wiped out, the computer forgets its inventory information and has to relearn it. To prevent this problem, computers have a small battery on their motherboards that maintains enough of a charge to prevent CMOS RAM from losing its data.
CMOS information is stored in CMOS RAM, which is volatile memory that maintains its information by using a battery stored on the system board.
VRAM
Video RAM (VRAM) is most commonly used on video accelerator cards to store values of pixels onscreen for refresh purposes. VRAM is the favored memory for video because it outperforms the other memory types because it is dual-ported memory: That is, it can be read from and written to at the same time. Comparatively, DRAM is single-ported, which means that the memory can be written to and read from, but not simultaneously — only one direction at a time. VRAM, however, allows you to do both simultaneously.
Video graphics cards today help relieve stress from the CPU because they have their own processor, a graphics processing unit (GPU) to handle the mathematical calculations related to graphics operations. These graphics cards also contain a large block of memory as well. Many graphics cards will contain video memory in the gigabytes with 2GB of VRAM not being enough to handle high-end games at high resolutions. Many gaming systems will require a video card with at least 4GB of VRAM to handle the high resolution of high-end games.
Identifying the Types of DRAM
DRAM is the most popular type of memory used in systems today. It is also the most popular type of memory that computer users add to their computers when upgrading memory. Therefore, you must understand the different types of DRAM and what types of DRAM outperform others.
Memory is organized into rows and columns, like a spreadsheet. Information is stored in the different cells, or blocks, that are created by the intersection of these rows and columns. With DRAM, the CPU requests data from the memory controller by sending the address of the row and the address of the column for every block of data that needs to be read. The memory controller then fetches the information from that memory location. Figure 3-1 shows two memory cells that hold data that the CPU wants to have.
FIGURE 3-1: Looking at how data is accessed in memory.
Synchronous DRAM
Synchronous DRAM (SDRAM) is memory synchronized to the system board speed. This synchronized speed means that the data stored in memory is refreshed at the system speed, and data is accessed in memory at the system speed as well.
SDRAM is one of the most popular types of DRAM found in earlier Pentium systems, such as the Pentium II. When you upgrade memory on your system and you determine that you need SDRAM, you then need to determine what speed of SDRAM. Because you are running at the system speed, you must match the DRAM speed with the motherboard speed. Thus, if you have a 100 MHz motherboard, you need 100 MHz SDRAM. If you have a 133 MHz motherboard, you need 133 MHz SDRAM.
For a 100 MHz motherboard, purchase 100 MHz memory, which is typically labeled PC100. Be aware, however, that there is some flexibility when purchasing SDRAM. For example, if when upgrading memory on a 100 MHz motherboard you can’t find PC100 memory because PC133 (which is SDRAM that runs at 133 MHz) is the popular memory right now, you can run the faster memory (133 MHz) on your 100 MHz motherboard, but know that it will only run at the speed of the board.
Rambus DRAM
When SDRAM was popular, a high-speed flavor of DRAM was on the market — rambus DRAM (RDRAM) — which runs at speeds around 800 MHz! RDRAM chips have a 16-bit internal bus width and are packaged together in a 184-pin, gold-plated memory module called a rambus inline memory module (RIMM). To take advantage of this type of memory, you need a motherboard and chipset that support RDRAM. Due to the cost of RDRAM, it lost the popularity contest to SDRAM and eventually DDR memory.
DDR
Double data rate (DDR) memory gets its name from the fact that it can transfer data twice during each clock cycle, compared with SDRAM that can transfer data only once per clock cycle. DDR memory ships in 184-pin DIMM modules (see the section “DIMMs,” later in this chapter) for desktop computers and 200-pin SODIMMs for laptop systems.
DDR memory speed is measured in MHz, like SDRAM is, and is labeled to indicate the speed. DDR memory labeling might look obscure at first because it also indicates the bandwidth by taking the speed and multiplying it by 8 bytes of data (64 bits). Here’s how to read DDR memory labeled as PC-1600: Divide the 1600 by 8 bytes to get the speed of the memory. In this case, you are looking at 200 MHz memory. PC-2700 runs at 333 MHz, and PC-3200 runs at 400 MHz. When you upgrade memory on systems that require DDR memory, you need to know the speed of the DDR memory.
Different RAM speeds for DDR memory are:
PC-1600 (200 MHz)
PC-2100 (266 MHz)
PC-2400 (300 MHz)
PC-2700 (333 MHz)
PC-3200 (400 MHz)
DDR2 and DDR3
Improvements to DDR memory have already started with DDR2 memory, which runs at speeds 400 MHz and higher, where DDR memory left off. DDR2 memory uses 240-pin memory modules and runs at 1.8 volts (V), as opposed to 2.5V for DDR memory. This results in less power consumption for more memory, which is great for laptop users.
Popular modules of DDR2 memory are:
PC2-3200 (400 MHz)
PC2-4200 (533 MHz)
PC2-5300 (666 MHz)
PC2-6400 (800 MHz)
The newer form of DDR memory is DDR3, which offers twice the data rate of DDR2 memory. One of the goals of DDR3 memory is to reduce power consumption; reportedly, DDR3 memory reduces power consumption by about 30 percent.
Common speeds of DDR3 are:
PC3-6400 (800 MHz)
PC3-8500 (1066 MHz)
PC3-10600(1333 MHz)
PC3-12800 (1600 MHz)
DDR memory modules are 240-pin DIMMs for desktop PCs and 204-pin SODIMMs for laptop systems. (Read more on DIMMs and SODIMMs in the next section.) Like DDR2, DDR3 memory is advertised by the speed and transfer rate. For example, DDR3-800 (also known as PC3-6400) is 800 MHz memory that has a throughput of 6400 MBps. DDR3-1066 (also known as PC3-8500) memory has a throughput of 8533 MBps. Another example is DDR3-1600, which is 1600 MHz memory with a transfer rate of 12,800 MBps.
Viewing memory type with CPU-Z
You can use a program known as CPU-Z to view the details on the type of memory on a system. Download CPU-Z from www.cpuid.com/cpuz.php and then run it on your system. Figure 3-2 shows that when I choose the Memory tab, I see the details on the type of memory installed in my system.
Whether you are purchasing or installing RAM, understanding the different types of memory packages available is important. The following sections identify different memory packages used in desktop computers and laptop systems.
DIMMs
Dual inline memory modules (DIMMs) are how we package and install memory today. A DIMM card holds a number of memory chips and has an edge connector containing a number of pins that make contact with the motherboard. This design makes it quite a bit easier to install memory than it was many years ago. In the past, you had to take a dual inline package (DIP) chip out of the system board and reinsert a new chip. Today, you purchase a card of chips (a DIMM) and install the DIMM into one of the DIMM sockets.
DIMMs supply information in 64-bit chunks. When installing memory into a system, you must install enough DIMMs to fill a memory bank, which is the number of DIMMs it takes to fill the data path of the processor. Because DIMMs are 64-bit modules, and the processors today are 64-bit, you only need to install one DIMM to fill a bank.
DIMMs come in different flavors that have a different number of pins on the modules. Older DIMMs use 168 pins for SDRAM and 184 pins for DDR memory, and newer DIMMs use 240 pin modules for DDR2 and DDR3 memory. DIMM modules and sockets are shown in Figure 3-3.
FIGURE 3-3: Looking at memory sockets on a motherboard.
The original DIMMs were 168 pins. DDR DIMMs come with 184 pins, and DDR2 and DDR3 DIMMs use 240-pin modules. DIMMs are also the most popular type of memory module that you will find in systems today, so they should be your focus when preparing for the A+ Exams.
SODIMM
Small outline dual inline memory modules (SODIMMs) are memory modules that are smaller than normal DIMMs and are used in laptops. A SODIMM comes in three different-sized modules: a 32-bit 72-pin module; a 64-bit 144-pin module (SDRAM); and a 64-bit 200-pin module for DDR and DDR2 laptop memory. Figure 3-4 compares a SODIMM and a DIMM.
A micro dual inline memory module (MicroDIMM) is another memory module used in laptop computers. The MicroDIMM is smaller than the SODIMM and comes in a 144-pin module for SDRAM and a 172-pin module for DDR memory.
Understanding Error-Checking Memory
Two primary types of error-checking memory have been used in systems over the years. The following sections introduce you to these two types of error-checking memory. Be sure to become familiar with them for the A+ Exams.
Parity versus nonparity
Parity memory is a type of error-checking memory, which is memory that verifies the information stored in memory is what is actually read from memory at a later time. Nonparity memory, comparatively, is memory that does not perform any kind of error checking to ensure that the data written to memory is what is actually read when it is retrieved.
Here’s how parity memory works. The two types of parity memory are odd and even. Both parity methods function the same way but differ in the sense of whether they look for an odd number of bits or an even number of bits. This discussion uses odd parity as the example.
With parity memory, for every byte (8 bits) of data written to memory, there is an additional ninth bit — the parity bit. When storing information to memory, the number of the enabled data bits (bits set to 1) written to memory are added up.
With odd parity, if an even number of data bits are enabled, the parity bit is set to 1 (enabled) so that there is an odd number of enabled bits in total written to memory. If the result of all the enabled data bits is odd, the parity bit is set to 0 (disabled) so that the odd number of enabled bits is retained.
After the parity bit has been set, the byte of data and the parity bit are written to memory. Even parity works the same way except that it looks for an even number of enabled bits; if the number of enabled bits is odd, the parity bit is enabled.
When the CPU requests data from memory, the data byte is retrieved along with the parity bit that was generated when the byte of information was stored in memory. The system looks at the data byte and calculates whether the parity bit stored in memory should be set to 1 or 0. It then compares the answer it has just generated with the value of the parity bit stored in memory. If the two match, the integrity of the information in memory is considered okay, the parity bit is stripped from the data byte, and the data is delivered to the CPU. If the two differ, you have a parity error, meaning that there is a problem with the integrity of the data stored in memory.
Parity memory cannot correct the error; it just reports that an error exists.
Remember that a parity error indicates something wrong with the integrity of data stored in memory.
ECC versus non-ECC memory
Error-checking and correction (ECC) memory is memory that can detect data integrity problems the way that parity memory can. (See the preceding section.) The difference between the two is that ECC memory can recover from the error and attempt to fix the problem with the data being read, whereas parity memory cannot. Memory that does not have ECC features is known as non-ECC memory as there are no error-checking and correction capabilities.
Multichannel Memory Architecture
The memory architecture in a system may depend on its age:
Older systems only used a single-channel memory configuration.
A single-channel configuration mandates a “single lane” used to send and receive information from memory.
When installing memory today, your system may support methods to increase memory throughput by using multiple channels.
Dual channel
With some of today’s systems, though, you can install memory in a dual-channel configuration, which allows for two 64-bit lanes to carry information to and from memory at the same time — resulting in better performance, as the amount of data sent at one time is doubled compared to that on a single-channel architecture. This configuration increases overall performance by allowing for more input/output per operation, or clock cycle.
To take advantage of dual-channel memory, you first need to ensure that your motherboard supports dual channel, as dual-channel memory is a function of the memory controller. You also need to be using DDR, DDR2, or DDR3 memory to take advantage of dual-channel architecture. If your motherboard supports dual-channel memory, you will install the memory modules in pairs. These pairs must be similar modules in capacity and speed. For example, when installing 4GB of RAM, you install two 2GB modules. When you install these modules, install them into the same color slots on the motherboard, usually colored either black or blue. If the motherboard does not color-code the memory slots, you install the pair of memory modules in the odd-numbered slots or the even-numbered slots — but not an odd and an even.
To leverage-dual channel memory, you must install the same memory modules in pairs. You must use the same type (for example, DDR2 or DDR3) of memory for both modules, the same speed, and the same capacity. The two modules must be similar because they need to be able to keep up with one another when performing parallel IO.
Triple and quadruple channel
Some systems today are supporting these architectures:
Triple-channel memory architecture allows three 64-bit lanes.
For example, Intel’s i7-900 series processors support triple-channel memory architectures.
Quadruple-channel memory architecture allows four 64-bit lanes.
The AMD G34 platform and the Intel LGA 2011 platform are examples of quadruple-channel memory architectures.
The same rules as dual channel memory apply when using triple and quadruple channel memory architectures: You must use similar memory modules, but you will be required to install either three modules (for triple-channel) or four modules (for quadruple-channel) at a time.
With both triple and quadruple channel architectures, if you only install a pair of modules, the system will run the memory in a dual-channel architecture.
You can purchase dual-channel or triple-channel memory kits to ensure that you are using the same type of memory and the same speed. You do not need to use these kits, but you are paying for the fact that someone has already tested the memory in a dual-channel configuration. Some benchmarks report that you can achieve a 65 percent increase in memory performance by using a multichannel configuration.
You can use CPU-Z to check to see whether you are running your memory in a single-channel, dual-channel, or triple-channel configuration (see Figure 3-5).
Memory modules are either single-sided or double-sided memory modules, but this characteristic does not mean that the memory chips exist on only one side of the memory card or both sides of the memory card (which is what most people think).
For single-sided memory, all the memory on the memory module is accessed at once by the system and is treated as a single “bank” of memory. It is important to note that the memory chips on a single-sided memory module may exist on both sides of the memory board.
For double-sided memory, the memory module (or memory board) is divided into two discrete chunks of memory (banks). The system can access only one bank at a time.
Original double-sided memory modules were created by taking two single-sided memory modules and connecting them.
Buffered versus Unbuffered Memory
When purchasing servers (a high-end system that provides services to the entire company) for an organization, you may come across the term buffered and unbuffered memory. Buffered memory, also known as registered, is memory that contains registers that are used to store data before sending it to the CPU. This stored data is retained for an extra clock cycle to act as a reliability feature. Buffered memory is typically found in network servers because they have many memory modules putting stress on the system where the extra reliability is needed.
Unbuffered memory is memory that does not have registers to store information and, as a result, the memory is not as reliable. The benefit of unbuffered memory is that it has less overhead (because it is not taking time to store information in registers) and therefore, it is faster memory than buffered memory.
Working with Cache Memory
Cache memory stores frequently used data and program code after it is read from slower DRAM. Cache memory is made up of SRAM, which is much faster than DRAM. The average speed of DRAM in the past was 60 ns, whereas the average speed of SRAM at the same time was 20 ns. If at all possible, you want the CPU’s request for information to be serviced by cache memory for a quicker response. To help service these responses, the system has different levels of cache memory: L1, L2, and now L3 cache, which is common on systems today.
L1 cache
Originally, Level 1 (L1) cache meant “internal cache” integrated into the CPU. This memory is typically a small amount of SRAM integrated into the processor’s chip, giving the processor instant access to this memory with no wait time. Wait time is how long it takes between when the processor requests information stored in memory and it actually receives that information.
Every pre-Pentium processor had L1 cache integrated into the processor chip, but the amount of L1 cache can vary. For example, the old 486 chips had 8K of L1 cache, whereas the original Pentium processors had 16K of L1 cache. Processors today have doubled that amount to 32K of L1 cache.
The L1 cache is typically divided into two parts:
Half the cache is used to store frequently accessed program instructions.
The other half of the cache stores frequently accessed program data.
L2 cache
Level 2 (L2) cache exists outside the CPU, usually on the motherboard or just outside the processor but in the processor casing. Therefore, some delay occurs when the processor accesses the information in L2 cache because of the distance between the processor and the L2 cache.
Originally, L1 cache was SRAM integrated into the processor’s chip, whereas L2 cache was SRAM located outside the CPU, on the system board. Today's systems have L1 and L2 integrated into the CPU.
One of the selling points of different processors is the amount of cache memory that comes with the processor. Many processors today typically have at least 32K of L1 cache and 512K, 1MB, 2MB, or more of L2 cache inside the casing of the processor. My Intel i7 system has 128 KB of L1 cache and 2 MB of L2 cache. The more cache memory a system has, the bigger the bucket to store more frequently used information.
Figure 3-6 shows the steps the processor takes to retrieve information:
When the processor retrieves information, it checks whether the information is stored in L1 cache (because L1 cache has no wait time).
If the processor does not find the information in L1 cache, it checks the next level — L2 cache.
If the information cannot be found in either L1 or L2 cache, the processor finally retrieves the information from system RAM.
FIGURE 3-6: How the CPU retrieves information from memory.
L3 cache
Because processors today provide a small amount of L1 cache and a large amount of L2 cache, the term L3 cache was used originally to identify cache that resides on the motherboard.
Today's processors are now marketing a third level of cache, known as L3, which is cache memory that resides on the processor that is shared between each processor core. This means that each core typically has its own L1 and L2 cache, while they share a larger amount (usually 6 to 8 MB) of L3 cache!
Viewing cache memory with CPU-Z
You can use the CPU-Z program to view the details on the type of cache memory that is present on the system. Figure 3-7 shows that I have the following types of cache on my system:
32 KB of L1 cache for program data (shown as D-cache).
The x4 means times the 4 cores on my system. This means that each core has 32 KB of L1 cache for program data.
32 KB of L1 cache for program instruction (shown as I-cache).
The x4 means times the 4 cores on my system. This means that each core has 32 KB of L1 cache for program instruction.
256 KB of L2 cache per processor core.
I have 4 cores on the system (denoted with a x4).
6MB of L3 cache. Notice this is not x4, so it therefore is shared cache for all the cores.
The discussion in this section focuses on issues related to memory upgrades. In general, upgrading memory is a simple task — assuming you purchase the proper type of memory for the upgrade. Factors that affect the proper type of memory are
Type of memory (FPM, EDO, SDRAM, DDR)
The speed of the memory
Pin connector type
Parity versus nonparity
The following sections discuss each of the factors that affect how you upgrade your system’s memory. Each of these factors contributes to the compatibility of the memory being installed in your system. In order for the memory to be compatible with your system you must
Install the correct type of memory.
Use the correct memory speed.
Install the memory in the correct configuration used by the system.
Type of memory
The first thing you need to know to upgrade your computer’s memory is which type of memory you need. You need to figure out whether you need to install a DIMM, MicroDIMM, or SODIMM. Desktop computers usually need a DIMM, while laptops use a MicroDIMM or SODIMM.
After you determine the memory module type, you need to determine the type of memory to install, such as DDR, DDR2, or DDR3 memory.
Speed
When you buy memory, you need to take into account the speed of the memory. Older memory, such as FPM or EDO memory, is typically measured in nanoseconds (ns) and ranges from 60 ns to 80 ns. With these types of memory, it is important not to mix speeds lest the system become unreliable. The speed of a SIMM is usually indicated on the chips themselves (displaying either a numeric value or a simple minus sign with a number). For example, a memory module running at 70 ns would show either 70 or –7 on the chips.
The speed of newer memory types, such as DIMMs and SODIMMs, is measured in MHz. When buying SDRAM or DDR memory, make sure to verify that you get the correct memory speed. For example, I recently upgraded the memory in the laptop I’m using to write this book. When I went to the store to buy a memory module, the first questions the in-store computer geeks asked were, “What type of memory?” and “What speed?” The system documentation or the CPU-Z program can help you determine the speed of memory needed. If you don’t have the documentation, be sure to look up the information on the manufacturer’s website.
Connectors
Another important issue with regard to memory installation is with the metal used on the memory modules. You need to purchase memory modules that use pins plated with the same metal used in the memory socket on the motherboard. Memory modules use silver- or gold-plated pins. If the SIMM socket, for example, uses silver-plated connectors, the memory module you purchase must use silver-plated pins. If you mix metal types, you will eventually have an unstable system.
Today’s preferred memory modules are gold-plated DIMM modules. Do not assume that you are using gold-plated DIMMs. Always ensure that you are installing the correct type of memory by checking the documentation for your system.
Using parity or nonparity?
The final issue with regard to memory upgrades is whether the system uses parity or nonparity memory. This information can be determined by checking the documentation that came with the system or by checking the system summary in CMOS. If you cannot find the information in CMOS or you misplace the documentation, try to find the information on the Internet at the vendor’s website. When you locate the information, use Table 3-1 to record the type of memory your system has so that you may refer to this when you perform a memory upgrade.
When installing memory, it is important to be familiar with RAM compatibility for the system. You need to ensure that you are installing the correct type of memory: SDRAM, DDR, DDR2, or DDR3. Also, be aware of the speed of memory your system takes. When adding memory to a system, faster memory is compatible with slower memory (as long as the type of memory is the same), but the downfall is that the faster memory will run at the lower speed if used.
Installing memory on desktop PCs
After you purchase the correct type of memory — meaning the correct type at the correct speed with the correct number of pins — you are ready to install the memory.
Take off the computer’s cover. You should see the DIMM slots on the motherboard, which are typically colored blue or black. Lightly, but firmly, place the DIMM in the socket and then push down and clamp either end in place with the clips available. Note that when you install the memory module, the memory module can only go in one way, as there are groves in the slot that the module has to sit in properly.
Lab 3-1 and Lab 3-2 can be downloaded from the book’s companion website: www.dummies.com/go/aplusaio. Use Lab 3-1 to practice finding out what type of memory you have; Lab 3-2 gives you practice installing memory on a desktop system.
Installing memory on laptop systems
Installing memory on today’s laptop systems is just as easy as installing memory on a desktop PC. The first step is to make sure you buy the correct type of memory for the laptop. Again, check the laptop documentation before heading to the store!
To install your memory, flip the laptop over. You’ll notice a door on the bottom of the laptop that can be removed (shown in Figure 3-8). This is where you add memory.
FIGURE 3-8: Remove the cover to add memory to a laptop.
After the cover is removed, you can insert the SODIMM into an empty slot by lightly placing the SODIMM into the memory slot on a slight angle and then clamping it back into place, as shown in Figure 3-9. If you are replacing memory, first remove the old memory module by pressing the clips on the side and then lifting out the old memory.
FIGURE 3-9: Inserting the SODIMM module into the memory slot.
When you have the SODIMM locked in place, put the cover back on.
Use Lab 3-3 for practice finding out what type of memory is needed by a specific laptop. In this lab, you research the laptop on the Internet. Lab 3-3 can be downloaded from the book’s companion website: www.dummies.com/go/aplusaio.
Getting an A+
This chapter provides an overview of the different types of memory and installation of memory. We touched on the following points:
Read-only memory (ROM) is memory that can be read from but not written to, and the information stored there is permanent.
Random access memory (RAM) is volatile memory that can be written to and read from; information stored there is flushed out when power is lost.
Dynamic RAM (DRAM) is memory that needs constant refreshing of its memory cells; it is also the type of memory that is typically upgraded on systems.
Static RAM (SRAM) is static memory, meaning that it does not need refreshing as often as DRAM does. SRAM is also faster than DRAM. SRAM is typically used for cache memory.
Today's systems have L1 and L2 cache unique to each processor core. A large amount of L3 cache is built into the processor that is shared between processor cores.
Memory is installed with memory modules. Whereas 72-pin SIMMs were popular in original Pentium systems, DIMMs are now the popular memory module for desktop systems. Laptops use SODIMMs as their memory module type.
You need to know the type of memory your system uses before you upgrade your system. For example, you need to note whether your system uses SDRAM or DDR memory. Also be sure to note the speed of the memory.
Prep Test
1.Which of the following types of memory is used for cache memory?
(A) SRAM
(B) DRAM
(C) EDO RAM
(D) SDRAM
2.You are a technician for a company and have been asked to install memory in a dual-channel configuration. Which of the following types of RAM can be installed?
(A) SDRAM
(B) DIMM
(C) Rambus
(D) DDR
3.You are assessing a system and trying to locate the cache memory. Where does the Level 1 (L1) cache reside?
(A) Motherboard
(B) Video card
(C) CPU
(D) BIOS
4.You are a technician for your company and you have been asked to upgrade the RAM on a salesperson’s laptop. What type of memory module will you install? (Select two.)
(A) DIMM
(B) SODIMM
(C) DRAM
(D) L1 cache
(E) MicroDIMM
5.Your manager is looking for memory that can protect against data corruption in the memory module. What feature is she looking for in her memory?
(A) ECC
(B) Parity
(C) Nonparity
(D) Dual channel
6.You are a technician for your company and have been asked by management to upgrade the RAM from 4GB to 8GB in all the desktop systems within the accounting department. You have purchased a number of DDR3 memory modules. Some of the desktops are currently running DDR2 and others are running DDR3. Which of the following represents the outcome of the upgrade?
(A) The DDR2 desktops can use the new DDR3 memory as long as the DDR3 modules are installed in the first slot.
(B) The DDR2 desktops can use the new DDR3 memory as long as the DDR3 modules are installed in the last slot.
(C) The DDR2 desktops can be upgraded as long as you alternate between the slots using DDR2 and DDR3 memory modules.
(D) The desktops using DDR3 are the only systems that can be upgraded.
7.How many pins does a DIMM have? (Select all that apply.)
(A) 64
(B) 128
(C) 168
(D) 32
(E) 184
(F) 196
(G) 240
8.You are upgrading the RAM on a desktop system and need to install RAM that is compatible with PC2-5300. Which of the following are compatible and would maintain the performance of the desktop?
(A) PC2-3200
(B) PC-2400
(C) PC3-6400
(D) PC2-6400
9.If memory data is corrupted, what type of error is created?
(A) File access error
(B) Parity error
(C) Disk error
(D) DRAM error
10.You are a service technician for your company. Your manager has asked you to install memory in the sales manager’s desktop. You notice that there are four memory slots in the desktop: Two slots are colored blue and two slots are colored black. In what configuration would you install memory in order to get the best performance?
(A) The slower memory should be installed in pairs within the black slots.
(B) Memory modules of the same size and speed should be installed in pairs in either the blue or the black slots.
(C) The slower memory should be installed in pairs within the blue slots.
(D) Alternate between the blue and the black slots as you install each memory module.
11.What type of memory is typically used for storing computer BIOS code?
(A) DRAM
(B) SRAM
(C) RAM
(D) ROM
12.You are installing two DDR2 memory modules: One is 800 MHz and the other is 600 MHz. Which of the following represents the speed at which both memory modules will run?
(A) 1400 MHz
(B) 800 MHz
(C) 600 MHz
(D) 200 MHz
13.How many DIMMs are used to fill a memory bank in an Intel i7 system?
(A) 1
(B) 2
(C) 3
(D) 4
Answers
A. SRAM is used for cache memory. DRAM — known as system memory — stores data and program code that are running. EDO and SDRAM are types of DRAM. See “SRAM.”
D. In order to take advantage of dual channel memory you must have a motherboard that supports it and be using DDR, DDR2, or DDR3 memory. Review “Multichannel Memory Architecture.”
C. L1 cache is cache memory integrated into the CPU, while L2 cache memory was originally external to the CPU and typically located on the motherboard. Check out “L1 cache.”
B and E. When installing memory in a laptop, you will use SODIMM or MicroDIMM memory modules as they are modules sized for laptops. Peruse “How Would You Like Your Chips Packaged?”
A. A feature of memory that allows it to fix data integrity and corruption is Error-Checking and Correction, or ECC memory. See “ECC versus non-ECC memory.”
D. Because you have purchased DDR3 memory you can only upgrade the RAM in systems that take DDR3, which would be the systems already using DDR3 memory. The systems using DDR2 memory are not compatible with DDR3 memory. Look over “RAM compatibility.”
C, E, G. DIMMs come in different flavors: 168-pin (for SDRAM), 184-pin (DDR), or 240-pin (DDR2 and DDR3) memory modules. The other choices for this question are just common numbers used in the computer field, but there are no memory modules that use those numbers of pins. Study “DIMMs.”
D. When upgrading RAM in a system, you need to ensure that the RAM is compatible with the existing memory. To be compatible, you must install the same type of memory of at least the same speed. You can install memory that is faster, but know that the memory will run at the lowest speed of the memory installed. Refer to “RAM compatibility.”
B. You’ll receive a parity error if there are any problems with data stored in memory. Examine “Parity versus nonparity.”
B. When installing memory in a system, try to install the memory into a dual-channel configuration to get the best performance possible. To do this, you must have two memory modules of the same speed and capacity and install those modules in slots that are paired for dual-channel configuration (either both blue slots, or both black slots). See “Multichannel Memory Architecture.”
D. A computer manufacturer’s BIOS/UEFI code is typically stored on read-only memory. Today’s version of the BIOS chip can be reprogrammed by running special software to update the BIOS. Check out “Read-only memory (ROM).”
C. The memory will run at the lowest common speed between the memory modules. This means that if using a 600 MHz and an 800 MHz memory module, the speed that both modules run at is 600 MHz. Peek at “RAM compatibility.”
A. Pentium 4s have 64-bit data paths, and a DIMM has a 64-bit data path as well. Thus, you need only one DIMM to fill a bank in a Pentium 4 system. Look over “DIMMs.”
Make sure you fully understand the different types of memory and their uses. You are sure to see a few questions on memory.
Software written to a ROM chip is firmware.
The lower the number of nanoseconds, the better the performance.
For a 100 MHz motherboard, purchase 100 MHz memory, which is typically labeled PC100. Be aware, however, that there is some flexibility when purchasing SDRAM. For example, if when upgrading memory on a 100 MHz motherboard you can’t find PC100 memory because PC133 (which is SDRAM that runs at 133 MHz) is the popular memory right now, you can run the faster memory (133 MHz) on your 100 MHz motherboard, but know that it will only run at the speed of the board.
Today’s preferred memory modules are gold-plated DIMM modules. Do not assume that you are using gold-plated DIMMs. Always ensure that you are installing the correct type of memory by checking the documentation for your system.
Lab 3-1 and Lab 3-2 can be downloaded from the book’s companion website: 
(A) DIMM