NOTE: If you install mixed pairs of PC2-5300 (DDR2 667-MHz) and PC2-6400 (DDR2 800-MHz) memory modules, the modules function at the speed of the slowest module installed. NOTE: Ensure that you install a single memory module in DIMM connector 1, the connector closest to the processor, before you install modules in any other connector. I have a P35 MB we spots for DDr2 ram. 2 are color coded red and 2 are color coded yellow EmmaBug03 The general rule of thumb is that DDR and DDR2 DIMMs should be inserted in alternating slots.

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By Darril Gibson
12/15/2012

Contents×

In this chapter, you’ll learn about two important concepts for any A+ technician to understand: random access memory (RAM) and central processing units (CPUs). A CPU is the brain of the computer, performing most of the processing, and RAM is used to store applications and data being used by the CPU. Both continue to be steadily improved and include a significant amount of technical detail that can easily confuse a regular user. This chapter will help you understand many of the terms used when describing them.

Exam 220-801 objectives in this chapter:

1.2 Differentiate between motherboard components, their purposes, and properties.
- CPU sockets
1.3 Compare and contrast RAM types and features.
- Types
  - DDR
  - DDR2
  - DDR3
  - SDRAM
  - SODIMM
  - RAMBUS
  - DIMM
  - Parity vs. non-parity
  - ECC vs. non-ECC
  - RAM configurations
    - Single channel vs. dual channel vs. triple channel
  - Single sided vs. double sided
- RAM compatibility and speed
1.6 Differentiate among various CPU types and features and select the appropriate cooling method.
- Socket types
  - Intel: LGA, 775, 1155, 1156, 1366
  - AMD: 940, AM2, AM2+, AM3, AM3+, FM1, F
- Characteristics
  - Speeds
  - Cores
  - Cache size/type
  - Hyperthreading
  - Virtualization support
  - Architecture (32-bit vs. 64-bit)
  - Integrated GPU
- Cooling
  - Heat sink
  - Fans
  - Thermal paste
  - Liquid-based

Exam 220-802 objectives in this chapter:

4.2 Given a scenario, troubleshoot common problems related to motherboards, RAM, CPU and power with appropriate tools.
- Common symptoms
  - Unexpected shutdowns
  - System lockups
  - Overheating

RAM

When technicians are talking about a computer’s memory, they are primarily talking about random access memory (RAM). RAM is used for short-term storage of applications or data so that the processor can access and use this information. In contrast, computers use hard drives for long-term storage of data.

Most RAM is volatile. This doesn’t mean that it’s explosive; it means that data in RAM is lost when power is removed.

As an introduction, the following list identifies commonly used types of RAM. All of these types of RAM are volatile.

Dynamic RAM (DRAM). Dynamic refers to how bits are stored in an electrical component called a capacitor. The capacitor holds the bit as a charge, but the capacitor needs to be regularly refreshed to hold the charge. This configuration uses very few components per bit, keeping the cost low, but the constant refresh reduces the speed.
Synchronous DRAM (SDRAM). SDRAM is synchronized with a clock for faster speeds. Almost all primary DRAM used in computers today is SDRAM, but it’s often listed as DRAM to avoid confusion with SRAM.
Static RAM (SRAM). Static RAM uses switching circuitry instead of capacitors and can hold a charge without a constant refresh. It requires more components per bit so it is more expensive, but due to how the switching works, it is quicker than DRAM. Due to the speed, SRAM is commonly used for CPU cache (described later in this chapter) but is rarely used as the primary RAM because of its cost.

Flash memory is very popular, but not as the primary RAM used in a system. USB flash drives, solid-state drives (SSDs), and memory cards used in cameras and other mobile devices all use flash memory. Flash memory is used for BIOS in many motherboards. Unlike DRAM and SRAM, flash memory is not volatile and retains data without power.

Double Data Rate SDRAM

While the original SDRAM versions were quick and efficient for their time, manufacturers have steadily improved them. Double data rate (DDR) is one of the improvements and is used in almost all SDRAM. As a reminder, SDRAM is tied to a clock, and when the clock ticks, data is transferred.

SDRAM uses only the leading edge for the clock. However, each of the DDR SDRAM versions uses both the leading and trailing edge of the clock. This is often called double pumping. Figure 3-1 compares the two over two cycles of a clock. You can see that SDRAM has two clocks from these cycles and that DDR has four clocks from the same two cycles.

Figure 3-1. SDRAM compared with double-pumping DDR.

The following list provides an overview of the different DDR versions:

Double Data Rate (DDR) SDRAM. DDR uses double pumping to double the data rate of SDRAM.
DDR2. DDR2 doubles the data rate of DDR. In addition to double pumping, it modifies the way that data is processed and can transfer twice as much data as DDR SDRAM.
DDR3. DDR3 doubles the data rate of DDR2. It uses double pumping and further modifies the way that data is processed. It can transfer four times as much data as DDR and eight times as much data as SDRAM.

DDR4 isn’t included in the objectives, but it is on the horizon as a replacement for DDR3. It’s expected to double the speed of DDR3.

DIMMs and SODIMMs

RAM comes on cards plugged into the slots in the motherboard. They are smaller than expansion cards, and technicians commonly call memory cards sticks. The two most common types of memory sticks are:

Dual in-line memory module (DIMM). A DIMM is the circuit board that holds the memory chips.
Small outline dual in-line memory module (SODIMM). SODIMM chips are smaller and are used in smaller devices such as laptop computers and some printers.

Figure 3-2 shows a DIMM (top) and a SODIMM (bottom).

DIMMs and SODIMMs have a different number of pins depending on the type used.

DDR SDRAM DIMM: 184 pins
DDR2 SDRAM DIMM: 240 pins
DDR3 SDRAM DIMM: 240 pins
DDR SDRAM SODIMM: 200 pins
DDR2 SDRAM SODIMM: 144 or 200 pins
DDR3 SDRAM SODIMM: 204 pins

Single Channel, Dual Channel, and Triple Channel

Ddr2 Slot Coloring Pages

Many motherboards and CPUs support single-channel, dual-channel, and triple-channel memory architectures. Each single channel represents a separate 64-bit line of communication that can be accessed independently. With dual channel, the system can access 128 bits at a time; triple channel gives it access to 192 bits at a time.

Using dual and triple channels provides an additional performance enhancement to DDR, DDR2, and DDR3, in addition to double pumping and other enhancements provided by the DDR versions. If you use a dual-channel motherboard with DDR3, it doubles the throughput of DDR3, providing 16 times more data throughput than SDRAM.

If you are upgrading a computer’s memory, it’s important to understand these channels. You can purchase DIMMs in matched pairs. Where you install each DIMM determines how many channels your system will use and can affect the performance of RAM.

Single Channel vs. Dual Channel

Dual-channel motherboards are very common. If you look at a dual-channel motherboard, you see that it has four memory slots, two slots of one color and two slots of another color. Figure 3-3 shows a diagram of four memory slots labeled for a motherboard using an Intel-based CPU. Slots 1 and 3 are one color, and slots 2 and 4 are another color.