CompTIA A+ Core Certification: The Basics of IT Hardware Part 2 - Installing RAM Types

220-1101: Objective 3.2: Given a scenario, install the appropriate RAM.

RAM is like a work table, in that it holds every project that the CPU is working on. The operating system, open applications, and all kinds of hidden processes use the RAM workspace when the device is running. If you get too many projects piled up onto a small work table, things get awkward and inefficient; the work will not go as smoothly as it could with more workspace. For a computer, adding more RAM is like getting a bigger table for sorting everything and spreading out for smoother working. Installing more RAM improves transfers between the CPU and both the RAM and hard drives.
The contents of RAM are temporary, and RAM is much faster than magnetic or SSD storage: RAM speed is measured in nanoseconds (billionths of a second), while magnetic and SSD storage is measured in milliseconds (thousandths of a second).
Ever-increasing amounts of RAM are needed as operating systems and applications get more powerful and add more features. Because RAM is one of the most popular upgrades to add to any laptop or desktop system during its lifespan, you need to understand how RAM works, which types of RAM exist, and how to add RAM to provide the biggest performance boost to the systems you maintain.
RAM is in a continual state of evolution, and it is no surprise that the list of RAM types has grown to be quite complicated—not just because there are so many developments, but because RAM is so often described in acronyms that do not define the differences of the types.

Table provides a review of RAM development.

Table: RAM Review

When you upgrade a computer, you need to know a few important details:
Form factor: Most computers in service use DDR3, DDR4, or DDR5. Laptops use SODIMMs of each DDR type.
Memory speed: If you plan to add a module, make sure it is the same speed as the existing module. If you plan to replace the modules, buy a matched set of modules in the fastest speed supported by the system.
Memory timing: The most common way to refer to memory timing is by its column address strobe (CAS) value. It is usually marked on the label with a CL value. If you install memory modules that use different CAS values, the computer could become unstable and crash or lock up.
Memory modules of the same type with memory chips of the same speed can have different CAS latency (CL) values. CL refers to how quickly memory column addresses can be accessed. A lower CL value provides faster access than a higher CL value. CL values increase when comparing different types of memory.
Most, but not all, memory module labels indicate the CL value. For modules that are not labeled, look up the part number for details.
Use the interactive memory upgrade tools available from major third-party memory vendors’ websites: These tools list the memory modules suitable for particular laptops, and some can be used to detect the currently installed memory. Crucial System Scanner is a useful tool for showing what is currently installed and what is compatible. For more information, visit www.crucial.com/usa/en/systemscanner.
Check the vendor’s memory specifications: You can determine part numbers by using this method, but it works best if memory must be purchased from the laptop vendor instead of from a memory vendor.
Synchronous DRAM (SDRAM) and DDR (double data rate) SDRAM were the first two generations of RAM in sync with the processor bus (the connection between the processor, or CPU, and other components on the motherboard). They used 168-pin and 184-pin DIMMs to attach to the motherboard. These are legacy versions and are mentioned here for perspective on the evolution of RAM. The following section discusses the types of RAM that are important to know.

Virtual RAM
Virtual RAM, or virtual memory (also known as the paging file), uses part of the hard drive to expand the RAM. This allows users to run more apps than the RAM could otherwise handle. To make adjustments to the virtual memory on a Windows 10/11 device, launch the search menu (Windows+S on the keyboard), type View Advanced System Settings, and press Enter. A System Property box appears with the Advanced tab active. Click the Settings button under Performance; then select the Advanced tab. From here, the virtual memory size can be changed by clicking the Change button under Virtual Memory (see Figure 3-24).



Adjusting Virtual Memory on a Windows Device


SODIMM Memory
As mentioned, laptops have a more compressed form factor than desktops; therefore, RAM for laptops needs to be smaller to fit the form factor. Laptops use small outline DIMMs (SODIMMs), which are reduced-size versions of DIMM modules. Figure 3-25 compares a typical DDR3 SODIMM with a DDR3 DIMM.



DDR3 SODIMM Module Compared to a DDR3 DIMM Module

Table: RAM Comparison (DIMM and SODIMM form factors and their uses)

DDR SODIMM keying is closer to the middle of the motherboard than with SDRAM SODIMMs.

†The keying on DDR3 is offset to one side, compared to DDR2.
‡The keying on DDR4 is different from the keying on DDR3, and they are not interchangeable.

DDR3 SDRAM
Compared to earlier RAM types, Double Data Rate 3 SDRAM (DDR3 SDRAM) runs at lower voltages, has twice the internal banks, and (with most versions) runs at faster speeds. DDR3 also has an 8-bit prefetch bus. DDR3 has greater latency. Typical latency values for mainstream DDR3 memory are CL7 or CL9, compared to CL5 or CL6 for earlier versions. Although DDR3 modules also use 240 pins, their layout and keying are different from previous types, and they cannot be interchanged.
DDR3 SDRAM memory can be referred to by the effective memory speed of the memory chips on the module (the memory clock speed x4 or the I/O bus clock speed x2)—for example, DDR3-1333 (333MHz memory clock x4 or 666MHz I/O bus clock x2) = 1333MHz). It also can be referred to by module throughput (DDR3-1333 is used in PC3-10600 modules, which have a throughput of more than 10,600MB/s, or 10.6GB/s). PC3 indicates that the module uses DDR3 memory.
Other common speeds for DDR3 SDRAM modules include PC3-8500 (DDR3-1066; 8500MB/s throughput), PC3-12800 (DDR3-1600), and PC3-17000 (DDR3-2133).
compares DDR, DDR2, DDR3, and DDR4 memory modules.



DDR, DDR2, DDR3, and DDR4 DIMM Desktop Memory Modules with Different Notch Locations


DDR4 SDRAM
DDR4 SDRAM, introduced alongside Intel’s X99 chipset for Haswell-E Core i-series processors in 2014, is the fourth generation of DDR memory. Compared to its predecessor, DDR3, DDR4 runs at lower voltage (1.2V) than either DDR3 or the lower-voltage DDR3L. DDR4 supports densities up to 16GB per chip (twice the density of DDR3) and twice the memory banks, and it uses bank groups to speed up burst accesses to memory; however, it uses the same 8-bit prefetch as DDR3. Data rates range from 1600Mb/s to 3200Mb/s, compared to 800Mb/s to 2133Mb/s for DDR3. To improve memory reliability, DDR4 includes built-in support for CRC and parity error checking instead of requiring the memory controller to support error checking (ECC) with parity memory, as in DDR3 and earlier designs.

DDR5 SDRAM: The Current Standard
DDR5 SDRAM was released in 2020 and is the fifth generation of DDR memory. Although DDR5 DIMMs has the same number of pins as DDR4 (288 pins), they are not compatible because the alignment key is located in an area on the RAM stick. In comparison to DDR4, DDR5 reduces power consumption (1.1V vs. 1.2V), offers twice the data transfer rate (6.4Gb/s vs. 3.2Gb/s) and has four times the memory density per chip (64GB vs. 16GB). DDR5 can include an onboard voltage regulator to gain higher speeds. In addition, the burst length in DDR5 is increased from DDR4’s 8 to 16. Burst length refers to the amount of data that is read/written after a single read/write command in SDRAM. The increase of burst length in DDR5 results in increased read/write efficiency.

Single Channel
Originally, all systems that used SDRAM were single-channel systems. Each 64-bit DIMM or SODIMM module was addressed individually.
Because RAM services the CPU, it is best to have RAM with enough speed to match the processing that the CPU performs. Dual-channel (and, later, triple-channel and quad-channel) RAM represents efforts to increase RAM speed for more efficient performance.

Dual Channel
Some systems that use DDR and most systems that use DDR2 or newer memory technologies support dual-channel operation. When two identical (same size, speed, and latency) modules are installed in the proper sockets, the memory controller accesses them in interleaved mode for faster access. This is why almost all RAM upgrades are done in pairs of chips.
Most systems with two pairs of sockets marked in contrasting colors implement dual-channel operation in this way: Install the matching modules in sockets of the same color (see Figure). See the instructions for the system or motherboard for exceptions.



Adding an Identical Module to the Light-Colored Memory Socket to Use Dual-Channel Operation on a Motherboard


Triple Channel
Triple-channel RAM is designed to triple the speed of the RAM bandwidth. Some systems that use the Intel LGA series chipsets support triple-channel addressing. Most of these systems use two sets of three sockets. Populate at least one set with three chips that have identical memory. Some triple-channel motherboards use four sockets, but for best performance, the last socket should not be used on these systems.

Quad Channel
Some systems that use the Intel LGA series chipset support quad-channel addressing. Most of these systems use two sets of four sockets. As in dual- and triple-channel systems, with quad-channel operation, you populate one or both sets with four chips of identical memory.
One point to remember about dual, triple, and quad memory is that the chips are not different for each; the difference is in the way the motherboard accesses the chips. Thus, it is technically possible (although not technically resourceful) to use only two of the same RAM chips in a quad system.

Parity vs. Nonparity
Two methods have been used to protect the reliability of memory:

1. Parity checking
2. ECC (error-correcting code or error correction code)

Both methods depend on the presence of an additional memory chip over the chips required for the data bus of the module. For example, a module that uses eight chips for data would use a ninth chip to support parity or ECC. If the module uses 16 chips for data (two banks of 8 chips each), it would use the 17th and 18th chips for parity. Parity checking, which goes back to the original IBM PC, works like this: Whenever memory is accessed, each data bit has a value of 0 or 1. When these values are added to the value in the parity bit, the resulting checksum should be an odd number. This is called odd parity. A memory problem typically causes the data bit values plus the parity bit value to total to an even number. This triggers a parity error, and the system halts with a parity error message. Note that parity checking requires parity-enabled memory and support in the motherboard. On modules that support parity checking, a parity bit exists for each group of 8 bits.
The method used to fix this type of error varies, depending on the system. On museum-piece systems that use individual memory chips, you must open the system, push all memory chips back into place, and test the memory thoroughly if you have no spares (using memory-testing software). If you have spare memory chips, you must replace the memory. If the computer uses memory modules, replace one module at a time and test the memory (or at least run the computer for a while), to determine whether the problem has disappeared. If the problem recurs, replace the original module, swap out the second module, and repeat.
Some system error messages tell you the logical location of the error so that you can refer to the system documentation to determine which module or modules to replace.
Parity checking has always been expensive because of the extra chips involved and the additional features required in the motherboard and chipset. It fell out of fashion for PCs starting in the mid-1990s. Systems that lack parity checking freeze up when a memory problem occurs and do not display any message onscreen.
Because parity checking “protects” you from bad memory by shutting down the computer (which can cause you to lose data), vendors created a better way to use the parity bits to solve memory errors: using a method called ECC.

Error Correction: ECC vs. non-ECC Memory
For critical applications, network servers have long used a special type of memory called >error correction code (ECC). This memory enables the system to correct single-bit errors and notify you of larger errors.
Although most desktops do not support ECC, some workstations and most servers do offer ECC support. On systems that offer ECC support, ECC support might be enabled or disabled through the system BIOS/UEFI, or it might be a standard feature. The ECC feature uses the parity bit in parity memory to determine when the content of memory is corrupt and to fix single-bit errors. Unlike parity checking, which only warns you of memory errors, ECC memory actually corrects errors.
ECC is recommended for maximum data safety, although parity and ECC do incur a small slowdown in performance in return for the extra safety. ECC memory modules use the same types of memory chips that standard modules use, but they also use more chips and might have a different internal design to support ECC operation. As with parity-checked modules, ECC modules have an extra bit for each group of 8 data bits.

To determine whether a system supports parity-checked or ECC memory, check the system BIOS/UEFI memory configuration (typically on the Advanced or Chipset screens). Systems that support parity or ECC memory can use non-parity-checked memory when parity checking and ECC are disabled. Another name for ECC is EDAC (error detection and correction).

Installing Memory
As mentioned earlier, upgrading RAM is one of the most (if not the most) common tasks a technician performs to improve a computer’s performance. When upgrading RAM, note that not all different types are compatible or interchangeable. For instance, a DDR3 RAM stick cannot be used in a DDR4 slot, and vice versa. A DDR3 DIMM has 240 pins, and a DDR4 DIMM has 288 pins. In addition, DDR4 DIMM and DDR5 DIMM are not compatible even though they have the same number of pins; the notches on both RAM sticks are in different locations, preventing installation into an incompatible slot. Different SODIMM types are also not compatible because they all have a different number of pins. This is an essential skill to learn and understand, so it is covered here. This section largely applies to both desktops and laptops.
Installing Memory Safely
When you install memory, be sure to follow the important safety procedures listed in Objective 4.4 of the 220-1102 Core 2 exam (see Chapter 9).

Preparations for Installing DIMM Memory
Before working with any memory modules, turn off the computer and unplug it from the AC outlet. Be sure to employ electrostatic discharge (ESD) protection in the form of an ESD strap and ESD mat. Use an antistatic bag to hold the memory modules while you are not working with them. Before actually handling any components, touch an unpainted portion of the case chassis, in a further effort to ground yourself. Try not to touch any of the chips, connectors, or circuitry of the memory module; hold them from the sides.

To install a DIMM module, follow these steps:
Step 1. Line up the modules’ connectors with the socket. DIMM modules have connections with different widths to prevent backward insertion of the module.
Step 2. Verify that the locking tabs on the socket are swiveled to the outside (open) position. Some motherboards use a locking tab on only one side of the socket.
Step 3. After you verify that the module is lined up correctly with the socket, push the module straight down into the socket until the swivel locks on each end of the socket snap into place at the top corners of the module (see Figure 3-27). A fair amount of force is required to engage the locks. Do not touch the metal-plated connectors on the bottom of the module; doing so can cause corrosion or ESD.
For clarity, the memory module installation pictured in Figure 3-28 was photographed with the motherboard out of the case. However, the tangle of cables and components around and over the DIMM sockets in Figure 3-29 provides a much more realistic view of the challenges you face when you install memory in a working system.



A DIMM Partly Inserted (Top) and Fully Inserted (Bottom)




DIMM Sockets Surrounded and Covered Up by Power and Data Cables or Aftermarket CPU Fans and Heat Sinks, Making It Difficult to Properly Install Additional Memory

When you install memory on a motherboard inside a working system, use the following tips to help your upgrade go smoothly and get the module to work properly:
If the system is a tower system, consider placing the system on its side to make the upgrade easier. Doing this also helps keep the system from accidentally tipping over when you push on the memory to lock it into the socket.
Use a digital camera or smartphone set for close-up focusing so that you can document the system’s interior before you start the upgrade process.
Move the locking tab on the DIMM sockets to the open position before you try to insert the module (refer to Figure 3-28). The memory module must be pressed firmly into place before the locking tab (left) will engage. The sockets shown in Figure 3-29 have closed tabs.
If an aftermarket heat sink blocks access to memory sockets, try to remove its fan by unscrewing it from the radiator fin assembly. This is normally easier to do than removing the heat sink from the CPU.
Move power and drive cables away from the memory sockets so that you can access the sockets. Disconnect the cables, if necessary.
Use a flashlight to shine light into the interior of the system so that you can see the memory sockets and locking tabs clearly; this enables you to determine the proper orientation of the module and to make sure the sockets’ locking mechanisms are open.
Use a flashlight to double-check your memory installation, to make sure the module is completely inserted into the slot and locked into place.
Replace any cables that you moved or disconnected during the process before you close the case and restart the system.
Note the positions of any cables before you remove them to perform an internal upgrade. You can use self-stick colored dots on a drive and its matching data and power cables. Marking masking tape with matching symbols works as well.