RAM Types and Features

RAM Types and Features

1. RAM is used for programs and data as well as by the operating system for disk caching (using RAM to hold recently accessed information). Thus, installing more RAM improves transfers between the CPU and both RAM and hard drives. If your computer runs short of RAM, the operating system can also use the hard drive as virtual memory, a slow substitute for RAM.

   • Memory Upgrade Considerations
     • Memory chip type used on the module (SDRAM, DDR SDRAM, and so on)
     • Memory module speed (PC3200, PC2-6400, PC3-12800, and so on
     • Memory module latency
     • Error checking (parity, non-parity, ECC)
     • Allowable module sizes and combinations
     • The number of modules needed per bank of memory
     • Whether the system requires or supports multi-channel memory (two or more identical memory modules accessed together instead of one at a time
     • The total number of modules that can be installed
     • Memory module form factor (240-pin DIMM, 184-pin DIMM, 168-pin DIMM, 204-pin SO-DIMM, and so on
   • SO-DIMM vs DIMM
     • In this section, you learn the differences between memory modules made for desktop and those made for laptop computers.
   • RAM Types
     • SRAM Static random-access memory (
     • SDRAM Synchronous DRAM
     • DDR SDRAM
     • DDR2 SDRAM
     • DDR3 SDRAM
   • Single-Sided vs Double-Sided
     • A single-sided (more properly known as single-ranked) module has a single 64-bit wide bank of memory chips. A double-sided (double-ranked) module has two 64-bit banks of memory stacked for higher capacity. Many, but not all, of these modules use both sides of the module for memory.
     • Some systems, primarily older systems using DDR2 or older memory technologies, have different maximum amounts of RAM based on whether single-sided or double-sided modules are used
   • RAM Configurations
     • Single-Channel Originally, all systems that used SDRAM were single-channel systems. Each 64-bit DIMM or SODIMM module was addressed individually.
     • Dual-Channel Some systems using DDR and most using DDR2 or newer memory technologies support dual-channel operation. .
     • Triple-Channel Some systems using Intel’s LGA 1366 chipset support triple-channel addressing. Most of these systems use two sets of three sockets.
     • Quad-Channel Some systems using Intel’s LGA 2011 chipset support quad-channel addressing. Most of these systems use two sets of four sockets. Populate one or both sets with identical memory.
   • RAM Compatibility
     • When it comes to memory, compatibility is important. The memory module type must fit the motherboard; speed must be compatible and the module storage size/combination must match your computer system as well.
     • However, to find out exactly which type of memory modules are compatible with your motherboard, visit a memory manufacturer’s website and check within its database. Be sure to have the model number of the motherboard or the model of the computer handy.
     • If you are installing memory in a system that uses single-sided modules (8 or 9 chips), don’t install double-sided modules (16 or 18 chips) as additional or replacement RAM unless you verify they will work in that system.
   • Installing Memory
     • Surprisingly, the CompTIA A+ 220-901 exam lists installing memory in laptops as an objective (220-901 objective 3.1), but it does not list installing memory in desktop computers.
     • Before working with any memory modules, turn the computer off 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.
     • Before actually handling any components, touch an unpainted portion of the case chassis in a further effort to ground yourself.