CertiGuide to A+ (Core Hardware)  9  Chapter 0011:  System Memory

DDR / PCxxxx 1 VIII  Chapter 00II: Summary

As we have discussed before, troubleshooting bad memory can be quite a challenge. If you're not using ECC RAM, you may have trouble finding the source of the error. Without the aid of any messages from the operating system, memory challenges can reveal themselves in many different ways. However, many common memory challenges are due in fact to the improper installation and configuration. The most common mistakes are:

• Improperly installed RAM
  
  
• Mismatched types of RAM
  
  
• Mismatch speeds of RAM
  
  
• Mismatch to manufacturers of RAM

Improperly installed RAM is simply not seating the RAM module all the way into its socket. It is quite uncommon with 168-pin SDRAM, and other modules where installing the module backwards is not possible. It is possible however, to install a SIMM module backwards.

The more common mistake is to try and install two different types of RAM on the motherboard. For example, when installing SIMMs, it is easy to install a standard DRAM in one socket, and EDO RAM in the other socket of the same bank. Another easy mistake to make is to install two different sizes modules of SIMMs in the same bank. You may also have challenges mixing ECC and non-parity memory units in a system. A possible workaround is to disable ECC mode in the BIOS, which may then allow you to use ECC modules as if they were standard DRAM.

Another common mistake is to buy RAM modules of similar size and type, yet mismatch speed of the RAM modules. Again sometimes with SIMM modules you can use RAM of one speed in one bank, and of a different speed in a separate bank. With the advent of higher performance SDRAM, an even more obscure challenge is that of mismatching the manufacturers of RAM. On more than one occasion I have seen two modules of RAM of the same type, size, and speed, not work together, and their only difference being who made them. As much as possible, you should always try to buy RAM of the same type, speed, and manufacturer. Following this simple guideline will prevent you from endlessly chasing your tail.

DDR / PCxxxx 1 VIII  Chapter 00II: Summary