Exam Preparation Tasks
RAM is used to hold programs and data as they are being used.
RAM’s contents are lost as soon as power is shut off or lost.
RAM upgrades are often needed during a system’s operational life to keep pace with the increasing requirements of operating systems and apps.
When specifying memory for a system, the memory module form factor, memory chip type, memory module speed, latency, error-checking features (or lack of same), and support for multi-channel memory must all be known to assure a compatible match.
SRAM (static RAM) is used for cache RAM to boost performance.
SDRAM (synchronous DRAM) was the first memory type to run in sync with the processor bus. All types of RAM in general use are based on SDRAM.
DDR SDRAM performs two transfers per clock cycle and has faster clock speeds than SDRAM.
DDR2 SDRAM can transfer data twice as fast as DDR.
DDR3 SDRAM has lower power consumption and can transfer data twice as fast as DDR2.
DDR4 SDRAM is an emerging standard with even lower power consumption and transfer rates twice the speed of DDR3.
Parity checking uses nine memory bits—eight for data and one for parity checking. It can detect memory errors but it cannot fix them.
ECC memory uses nine memory bits but is able to fix single-bit memory errors. It is common in servers.
Buffered (registered) memory is used in many servers and some workstations or desktops. The buffer chip helps maintain stability when large amounts of RAM are installed, but it slows down the system slightly.
SO-DIMM (SODIMM) modules are used primarily in laptops as a small form factor equivalent to full-size DIMM modules. They are available in the same memory types as regular DIMMs.
Single-channel systems address a single DIMM as a logical memory bank. Dual-channel, triple-channel, and quad-channel systems address two, three, or four identical modules (same size, speed, and latency) as a logical bank for faster memory access.
Single-sided modules actually have a single bank of 64-bit memory chips, while so-called “double-sided” modules have two banks of 64-bit memory, which might or might not use both sides of the module.
When installing memory modules, be sure to use ESD protection, to line up the module with the socket, and to push it into place until the locking tab or tabs swivel up into place.
On some systems, it might be necessary to relocate or temporarily disconnect power or data cables or even remove the cooling fan from the CPU heatsink to gain access to memory slots.
Review All the Key Topics
Review the most important topics in the chapter, noted with the key topics icon in the outer margin of the page. Table 4-2 lists a reference of these key topics and the page numbers on which each is found.
Table 4-2 Key Topics for Chapter 4
Key Topic Element
Desktop memory modules compared
DIMM and SO-DIMM modules compared
A DIMM partly inserted (top) and fully inserted (bottom)
DIMM sockets surrounded by cables
Complete the Tables and Lists from Memory
Print a copy of Appendix B, “Memory Tables” (found on the CD), or at least the section for this chapter, and complete the tables and lists from memory. Appendix C, “Answers to Memory Tables,” also on the CD, includes completed tables and lists to check your work.
Define Key Terms
Define the following key terms from this chapter, and check your answers in the glossary.
paging file (virtual memory)
Complete Hands-On Lab
Complete the hands-on lab, and then see the answers and explanations at the end of the chapter.
Lab 4-1: Select and Install the Correct RAM
Scenario: You are a technician working at a PC repair bench. You are required to install two sticks of DDR3 RAM into the first channel of the dual channel memory slots in a motherboard. When completed, this should form a “bank” of memory.
Procedure: Select the proper RAM memory modules from the figure and “place” them within the proper memory slots on the motherboard by checking off the correct RAM modules and memory slots in Figures 4-7 and 4-8.
Figure 4-7 Lab 4-1 memory modules.
Figure 4-8 Lab 4-1 memory sockets.
Answer Review Questions
Answer these review questions and then see the answers and explanations at the end of the chapter.
Which of the following loses its contents when you shut down the computer?
Hard disk drive
USB flash drive
Identify the type of RAM in the following figure.
A system that uses matched pairs of memory modules supports which of the following?
Which two methods are used to protect the reliability of memory? (Select the two best answers.)
ECC (error-correcting code)
Most types of desktop memory modules use which kind of memory?
Unbuffered non-ECC memory
Critical applications and network servers use a special type of memory. What is it called?
Identify the type of memory layout this module uses.
With ECC, with register (or buffer)
With ECC, no register (or buffer)
No ECC, with register (or buffer)
No ECC, no register (or buffer)
To correctly install a DIMM module, what should you do? (Choose all that apply.)
Line up the module connectors with the socket.
Verify that the locking tabs on the socket are swiveled to the outside (open) position.
Verify that the module is lined up correctly with the socket. Then push the module straight down until the locks on each end of the socket snap into place at the top corners of the module.
None of these options is correct.
You have a dual-channel motherboard. You have two identical 4GB DDR3 modules and two identical 2GB DDR3 modules. In the following diagram, one module of 4GB DDR3 is being installed in the first blue slot. Where should you install the second 4GB DDR3 module for best results?
Install the second 4GB DDR3 in the second blue slot.
Install the second 4GB DDR3 in the first black slot.
Install the second 4GB DDR3 in the second black slot.
It does not matter as long as all the modules are DDR3.
Which of the following types of RAM is also known as PC3-10600?
Answers and Explanations to Hands-On Labs
Lab 4-1: Select and Install the Correct RAM
The first set of RAM (DDR3) should have been selected. Note that DDR3’s center notch is to the left of the older DDR2 and DDR center notch. The memory modules should have been installed to the DIMM1 (blue) slot of Channel A and the DIMM2 (blue) slot of Channel B, collectively forming the first bank of RAM. (See Figures 4-12 and 4-13.)
Figure 4-12 Lab 4-1 solution.
Figure 4-13 Lab 4-1 solution.
The memory notch should be aligned with the slot’s corresponding notch, and then placed in the slot and pressed down until the ears lock into place. When installing RAM, try not to touch the chips or connectors. Handle the RAM from the sides and press down on the RAM with your thumbs after it has been placed in the slot.
Answers and Explanations to Review Questions
C. Random access memory (RAM) loses its contents when the computer shuts down. Hard disk drives, USB flash drives, and Read-Only Memory (ROM) are designed to retain their contents even when they are not receiving power.
C. DDR3. The label identifies this module as PC3, which indicates that it contains DDR3 type RAM.
B. Dual-channel support requires that both paired memory slots use memory with identical specifications.
A, C. Parity memory and ECC have an additional memory chip added for parity. They are both methods used to protect the reliability of memory.
A. Unbuffered, non-ECC memory is used in most common desktop computers sold in the market. This kind of memory is also used in some servers and workstations.
A. ECC memory enables the system to correct single-bit errors and notify you of larger errors.
A. With ECC, with register (buffer). The memory module in the diagram contains 18 memory chips (2 banks of 8 each, plus a parity or ECC chip) and an additional chip that contains the register (or buffer).
A, B, C. To correctly insert the memory modules, you should follow all the steps listed. You might also have to use a fair amount of pressure to securely lock these modules in place.
B. For best results, you should always install identical modules in the same channel. The two 4GB modules should be the same size, speed, latency, and so on, and should be installed in the same channel (in this case, in the two blue slots). The same is true for the two 2GB modules, which should be installed in the two black slots. The slots on this motherboard are color-coded to indicate the channels. Always check your documentation for the correct orientation of the channels and the type of RAM your motherboard will accept.
C. DDR3-800 is also known as PC3-6400 (6400MBps peak transfer rate). DDR3-1066 is also known as PC3-8500 (8500MBps peak transfer rate). DDR3-1333 is also known as PC3-10600 (10667MBps peak transfer rate). DDR3-1600 is also known as PC3-12800 (12800MBps peak transfer rate).
Answers to Review Questions:
A and C
A, B, and C