Linux – Running Linux OS in ram only

Here is a eHow page on How to Dump Linux Memory

Linux provides two virtual devices for this purpose, '/dev/mem' and '/dev/kmem', though many distributions disable them by default for security reasons. '/dev/mem' is linked to the physical system memory, whereas '/dev/kmem' maps to the entire virtual memory space, including any swap. Both devices work as regular files, and can be used with dd or any other file manipulation tool.

That leads to the ForensicsWiki page on Memory Imaging Tools with the Linux/Unix section,

1. dd On Unix systems, the program dd can be used to capture the contents of physical memory using a device file (e.g. /dev/mem and /dev/kmem). In recent Linux kernels, /dev/kmem is no longer available. In even more recent kernels, /dev/mem has additional restrictions. And in the most recent, /dev/mem is no longer available by default, either. Throughout the 2.6 kernel series the trend has been to reduce direct access to memory via pseudo-device files. See, for example, the message accompanying this patch: http://lwn.net/Articles/267427/. On Red Hat systems (and derived distros such as CentOS), the crash driver can be loaded to create a pseudo-device for memory access ("modprobe crash").
2. Second Look This commercial memory analysis product has the ability to acquire memory from Linux systems, either locally or from a remote target via DMA or over the network. It comes with pre-compiled Physical Memory Access Driver (PMAD) modules for hundreds of kernels from the most commonly used Linux distributions.
3. Idetect (Linux)
4. fmem (Linux)
   fmem is kernel module, that creates device /dev/fmem, similar to /dev/mem but without limitations. This device (physical RAM) can be copied using dd or other tool. Works on 2.6 Linux kernels. Under GNU GPL.
5. Goldfish
   Goldfish is a Mac OS X live forensic tool for use only by law enforcement. Its main purpose is to provide an easy to use interface to dump the system RAM of a target machine via a Firewire connection. It then automatically extracts the current user login password and any open AOL Instant Messenger conversation fragments that may be available. Law Enforcement may contact goldfish.ae for download information.

See Also: Linux Memory Analysis.
There is also GDB commonly available on most Linuxes.
And, you are always advised to avoid writing over unknown memory -- it can lead to system corruption.

To begin with, to use that amount of memory, you need to have a 64-bit Operating system.

Next, I would check the chipset of your laptop's motherboard (can usually be seen at startup, usually one letter and two numbers. Then look up the specification. I can't comment for certain, but a lot of laptops of Core 2 age don't support more than 4GB of memory.

edit -- update

Sorry, your laptop will NOT be able to support 8GBs, I saw the model number you wrote above and tracked it down as a Satellite A300-1J1, this has a GM965 Chipset, and from Intel's specifications, it states that the maximum amount of supported memory is 4GBs