CompTIA A+ Training Kit: Understanding RAM and CPUs

Chapter Summary

• Systems use synchronous dynamic RAM (SDRAM) for primary memory. Static RAM (SRAM) is used for L1, L2, and L3 cache. Common versions of SDRAM are DDR, DDR2, and DDR3.

• Memory comes on circuit cards called DIMMs for desktop computers and SODIMMs for laptops. DIMMs and SODIMMs come in different sizes for different DDR versions.

• Dual-channel and triple-channel RAM provide additional 64-bit paths for transferring data to and from RAM. When installing multichannel DIMMs, install matched sets in the same bank. Banks are normally the same color. On an Intel dual-channel motherboard, Bank 0 includes slots 1 and 3.

• A triple-channel motherboard has six slots for RAM, and RAM should be purchased in matched sets of three DIMMs.

• The speed of RAM is tied directly to the clock. The formula to calculate DDR3 RAM speed is: Clk x 4 x 2 x 64 / 8. For a 200-MHz clock, the speed is 200 x 4 x 2 x 64 / 8, or 12,800 MB/s.

• The DDR3 standard name is derived from the clock x 8. For a 200-MHz clock, the DDR3 standard name is DDR3-1600. The module name is derived from the overall speed. The DDR3 module name with a 200-MHz clock is PC3-12800.

• If matched DIMMs are not used and a bank includes different speed DIMMs, the bank will default to the slowest speed.

• CPUs come in 32-bit and 64-bit versions, referring to how many bits they use to address memory. If you want to use more than 4 GB of RAM, you need a 64-bit CPU and a 64-bit operating system.

• Multiple-core CPUs include more than one fully functioning processor, and the operating system views each core as a separate CPU. Intel uses hyper-threading, which allows each core to process two threads at a time, and each core using hyper-threading is treated as a separate CPU by the operating system.

• CPUs use fast static RAM (SRAM) as cache to improve processing. They commonly include L1, L2, and sometimes L3 cache. L1 is fastest and closest to the CPU, and L3 is slowest and farthest away. L1 is smallest, and L3 is the largest. When the CPU needs data, it looks in L1, then L2, and then L3.

• The speed of the CPU is based on the speed of the clock and a multiplier. It is usually listed as the multiplied speed, such as 3.4 GHz. Intel uses Turbo Boost and AMD uses Turbo Core to modify these speeds during operation.

• Most CPUs support virtualization. Intel refers to its support as VT-x, and AMD calls its support AMD-V. These settings can be enabled in BIOS on most systems.

• An integrated GPU refers to a graphics processor embedded within a CPU. AMD calls some of its integrated GPU chips APUs.

• Common Intel CPUs are Core i3, Core i5, and Core i7 series. Most Intel CPUs use LGA sockets. Common Intel sockets are: LGA 775 (Socket T), LGA 1366 (Socket B), LGA 2011 (Socket R), LGA 1156 (Socket H or H1), and LGA 1155 (Socket H2).

• Common AMD CPUs are Sempron, Athlon, and Phenom. Most AMD CPUs use PGA sockets, and common sockets are: Socket 940, AM2, AM2+, AM3, AM3+, FM1, and Socket F.

• CPUs are commonly kept cool with heat sinks and fans. When replacing a CPU, use thermal paste between the CPU and the heat sink. Liquid cooling is an advanced cooling practice.

• Hardware problems that can cause unexpected shutdowns and intermittent fails include overheating due to failed fans or inadequate ventilation, faulty power supply, or faulty RAM.

• Use a software memory tester to test RAM.