Question : Problem: Memory / Motherboard Installation Question

I work with a guy who is part of the help desk team at the company I work for.  He is taking IT related classes at a local community college.  He was having problems answering two memory related questions so he asked me for help.  I work with Cisco equipment not PC's so I didn't have an answer for him.  To help him out I figured I'd post the questions here to see if any of you have answers.  The questions are very vague.  They don't mention what type of memory is used or what type of motherboard the memory is being installed on.  Here are the questions exactly as my co-worker sent to me.  If you have any decent answers for these please post them.  I'm sure he would appreciate it.  I'd kinda like to know the anwsers too.  :)

What is the disadvantage of using two 64MB modules instead of a single 128MB module in a system with three slots for memory modules?

What are two disadvantages of using one 256MB modules rather then two 128MB modules?
 

Answer : Problem: Memory / Motherboard Installation Question

As you expand system memory, using smaller modules will limit the maximum memory available in a system.  For example, a Motherboard has a limit of 1.5gb of Ram and can take a maximum of 512mb in each slot.  If you use 2 64mb modules, the maximum memory you could put in the system is by adding 1 512 in the empty slot for a total memory onboard of 640mb.   If though you use 1 128mb module, you could add 2 512's to the empty slots giving you a total onboard memory of over 1gb.

2 Disadvantages,

Failure of the single 256 module will bring down the system, whereas failure of 1 128mb module will still leave the PC with 128mb Ram.  Secondly, if the memory is installed in a newer board and is capable, multiple modules can have greater performance over single modules, depending on the motherboard.
Third, Typically the larger the memory module the greater the cost, usually OVER double the cost of 2 singles.