3.6 Memory Installation

5) You have an older computer that has four DDR2 memory slots. Currently, there are two 512-MB memory modules installed. You check the motherboard documentation and find that the system has a 4-GB memory limitation. You want to add more memory to this system. What is the maximum total amount of usable RAM you can have in this system by adding new memory modules (and without replacing the existing memory modules)? - 4.5 GB - 3.5 GB - 3 GB - 2 GB - 1.5 GB - 4 GB

- 3 GB

1) You want to build a new system that supports 16 GB of memory. Which of the following is the MOST important consideration when building the computer? - DDR3 memory - 64-bit processor - CAS latency - ECC memory

- 64-bit processor

2) You work as the IT administrator for a small corporate network. Sam, an employee in the support department, wants to run a virtual machine on his computer for troubleshooting customer issues, and he needs a very stable computer from which to work. You need to decide whether to install buffered or non-buffered RAM in his computer. Which of the following BEST describes the reason to choose buffered instead of unbuffered memory for this new computer? - Buffered memory reduces the load on the memory controller and allows the system to be more stable. - Buffered memory is faster and less expensive. - Buffered memory reduces the load on the memory controller, but due to the extra clock cycle, is less stable. - Buffered memory increases the load on the memory controller, but is faster and more stable.

- Buffered memory reduces the load on the memory controller and allows the system to be more stable.

3) With a memory module read request, there is a delay between the time of the data request and the time the data is available for output from the memory module. What is this delay called? - CAS latency - Capacity - Clock cycle parity - Frequency

- CAS latency

10) You have an existing system that has a single DDR3 memory module installed. You would like to add more memory to the three remaining empty memory slots. Which of the following steps should you take to make sure that you get the right memory for the system? (Select two.) - Update the BIOS and then purchase the newest memory modules available. - Purchase the slowest modules to ensure compatibility. - Purchase the fastest modules possible. - Check the motherboard documentation to find which modules are supported. - Purchase additional modules that are the same as what is currently installed.

- Check the motherboard documentation to find which modules are supported. - Purchase additional modules that are the same as what is currently installed.

7) You are in a carpeted office lighted by fluorescent bulbs. You are preparing to add memory modules to a user's computer. The user has already unpacked the memory modules and stacked them on top of an old, unused CRT monitor. What is the greatest threat to these memory modules in this environment? - The magnetic field around the CRT monitor. - High-voltage discharge from the CRT monitor. - Electrostatic discharge (ESD). - Electromagnetic interference (EMI) from the fluorescent lights.

- Electrostatic discharge (ESD).

8) Which of the following is the most common method for removing RAM from a motherboard? - Move the tabs holding the RAM out of the way; then pull straight up to remove the RAM. - Pull the RAM module up from one corner and then twist to release the other corner. - Remove the screw from the one side; then pull straight up to remove the RAM. - Tip the RAM module at a 45-degree angle while pulling on it.

- Move the tabs holding the RAM out of the way; then pull straight up to remove the RAM.

6) Which of the following statements is true regarding single- and double-sided memory? - Double-sided RAM always has modules on both sides of the circuit board. - Single-sided memory uses half the number of memory modules as double-sided memory of the same capacity. - Single-sided RAM can be organized into two banks. - Double-sided RAM allows the computer to access all of the memory.

- Single-sided memory uses half the number of memory modules as double-sided memory of the same capacity.

4) You have just upgraded the memory in one of your network servers by adding two 4-GB ECC memory cards. Before purchasing the new memory, you made sure that the modules fit in the memory slots (packaging) and the speed (memory frequency) was supported by the memory controller. What did you forget to check that would significantly impact the memory checking of your new ECC memory cards? - Whether or not the existing memory modules support ECC. - Whether or not the existing memory modules support parity RAM. - Whether or not the new memory modules are buffered. - Whether or not the new memory modules are single- or double-sided.

- Whether or not the existing memory modules support ECC.

9) You are trying to push a memory module into a memory slot, but it is not seating properly. What is the MOST likely issue? - You are trying to install a single-sided memory module in a double-sided slot. - You need to push down the slot tabs and move them back. - You need to clear debris from the memory slot. - You are trying to install the memory module backwards in the memory slot.

- You are trying to install the memory module backwards in the memory slot.

Column address strobe or signal (CAS) latency

Another factor that affects the performance of memory is the latency associated with accessing data in RAM. With a read request, the CAS latency (CL) is a delay between the time the data is requested and the time that the data is available on the module's output pins. Older memory expressed the delay in nanoseconds, but DRAM uses a ratio based on the clock frequency to describe the delay. For memory modules of the same type and frequency, a lower CAS number indicates less delay (i.e., faster RAM). Because CL is related to the frequency, you cannot directly compare the CL between modules with different frequencies. For example, a DDR2 module operating at 533 MHz with a CL of six has more delay than a DDR3 module at 667 MHz with a CL of seven. In addition to CL, memory timings collectively refers to other memory characteristics that describe the delay for performing other types of operations. For stable operations, the bus takes into account these latencies to keep the bus and the memory synchronized. Manufacturers test memory modules and rate them based on the operating frequency and the timing characteristics. - Settings that produce stable performance are encoded into the SPD module on the memory. - The BIOS reads this information to know how to configure memory settings on the motherboard. For many systems, you can manually modify the memory timings and frequency. - Running RAM at a lower clock speed enables you to decrease the CAS latency setting. - Increasing the frequency must usually be compensated for by increasing the CL (and other) settings.

Buffered (registered)

Buffered RAM holds memory addresses or data in a buffer before it is transferred to the memory controller. Buffered RAM improves stability on systems with a lot of RAM (over 1 GB). Buffered RAM might slow system performance. ECC modules are typically buffered. Buffered RAM must be supported by the motherboard. Some motherboards require buffered memory. Unbuffered memory does not have a buffer to hold memory addresses or data before it is transferred to the memory controller. Common workstations and laptops use unbuffered memory. Servers and high-end workstations use buffered memory.

Error correcting code

Error correcting code (ECC) memory is a type of memory that detects and corrects the common kinds of internal data corruption. ECC memory is also called parity memory. With ECC, a value is appended to the end of each byte so that the value of the data can be compared and recalculated if an error occurs. ECC is an improvement on parity techniques because errors in more than one bit can be detected and corrected. Keep in mind the following facts about error correcting memory: - Memory modules with ECC have extra memory chips on the module (typically 9 modules instead of 8). If the number of chips is divisible by 3 or 5, the module is ECC memory. - ECC or parity memory must be supported by the motherboard. - Because it is more expensive than non-ECC, ECC memory is typically used only in servers. - ECC memory is slower than non-ECC memory. - Do not mix ECC and non-ECC memory in a system. Mixing ECC and non-ECC memory disables the error correction function. You might hear the terms parity and ECC used interchangeably. However, parity RAM checks only for errors; ECC RAM checks and corrects errors.

Frequency

For optimal performance, you should match the memory frequency (sometimes called the speed) with the frequency supported by the system bus/memory controller. You can install slower memory in the motherboard, but this will degrade performance. You can install faster memory in the motherboard, but it will operate only up to the maximum supported by the motherboard. When you mix memory with different frequencies, all memory will operate at the lowest frequency. Most memory modules include an EEPROM chip that identifies its frequency. The BIOS uses the information in this chip to set the frequency automatically. On many systems, you can edit the BIOS manually to change the frequency. If the BIOS does not configure memory to run at its highest rated speed, then do the following: - Verify that the motherboard supports that speed. You might be able to update the BIOS to support faster memory. - The serial presence detect (SPD) on the memory is often set below the maximum rating for the memory. To use the maximum speed settings, you can manually configure the speed and timing settings for the memory (if the motherboard allows you to do this).

Parity RAM

Parity memory is a type of memory that checks for common kinds of internal data corruption. It does not correct internal data corruption. Non-parity memory does not perform error checking. Parity RAM is no longer used. Today, PC systems use ECC for error detection and correction.

Single-sided/double-sided RAM

Single-sided RAM has memory modules that are organized into a single logical bank; double-sided RAM has modules organized into two banks. The computer can access data in only one bank at a time. Therefore, single-sided RAM allows access to all the memory; double-sided RAM requires the computer to switch between banks. Originally, double-sided RAM had modules on both sides of the circuit board, and single-sided RAM had modules on only one side. However, you can also have double-sided RAM with modules on only one side. The memory is divided into separate banks internally. Single-sided memory of the same capacity as double-sided memory uses half the number of memory modules. The modules are denser, with a higher individual capacity. Most motherboards support both single-sided and double-sided memory. However, verify compatibility before purchasing. The use of single-sided and double-sided RAM varies among motherboards. You might find older motherboards: - Are unable to use double-sided memory. - Allow double-sided memory but can use only up to half the total memory when all memory slots are filled. - Do not allow mixing single-sided and double-sided together.

Capacity

The capacity (sometimes called the size) refers to the storage capacity of the memory module (e.g., 256 MB, 512 MB, 1 GB). The total capacity of memory that you can install in a system is limited by: - The number of memory slots on the motherboard. - The maximum total capacity that can be installed. For example, most systems will have a maximum capacity of between 3 GB and 16 GB of RAM. - The maximum module capacity. For example, the motherboard might be able to accept only up to 2 GB or 4 GB modules. - The maximum amount of memory that can be addressed (used) by the operating system. A 32-bit operating system can use between 3 GB and 4 GB of memory, while a 64-bit operating system can use much more. ---You can install more than 4 GB of memory in a system that uses a 32-bit operating system; however, the operating system can use only between 3 GB and 4 GB of that memory.