Ram Memory or Random Access Memory is physically a Card that has a combination of chips soldered onto it to achieve the resultant amount of ram designated on the chip (128 Mb, 256 Mb, 512 Mb or 1024 Mb - 1Gb in total ram). When you turn off your computer all the stuff (programs and data) gets "flushed" or emptied out of the chip and when you restart your computer things are reloaded again. Ram is for running programs when the computer is running. The things you need to know about ram as a computer user or consumer is that each computer new or old has Ram. Over the years there were and still are quite a variety of types of ram.
Briefly, RAM memory is used by the system to store data in the form of files for processing by a computer's central processing unit (CPU), also known as the processor. The processors used in most PCs are made by Intel and AMD. The processor runs the program and data files according to instructions given to it by the operating system, which, on PCs, is usually a version of Windows, or, to a much lesser extent, a version of Linux.
The amount of RAM memory used in modern computers is expressed in megabytes (MB) and gigabytes (GB). A gigabyte (1GB) is 1024MB. Most new desktop and laptop computers that come with Windows Vista preinstalled should have a minimum of 2GB or RAM memory.
The RAM memory used in current PCs comes in the form of DDR and DDR2 and DDR3 memory modules.
Unless all of the memory slots on a computer's motherboard are already fitted with memory modules, the RAM memory in most desktop and laptops computers can be increased by installing more memory (upgrading the memory). Installing one or more additional memory modules in a desktop or a laptop computer is a simple process of undoing the clips on the sockets that hold the chips.
Most of the current (July 2008) desktop PCs and laptop PCs have motherboards that use DDR or DDR2 memory. However, DDR3 memory is now available, so, as time goes on, more motherboards will be using it.
Generally speaking running 512 Mb ram is sufficient for most of what people are running at home (except games and certain desktop publishing programs which require more).
Hard drive is the permanent storage device that always keeps your programs and data. It is the device that the document goes to when you save it or your program goes to when you install it. For most people using the internet and creating documents and things 40 Gb hard drive is enough. If you are manipulating dvds or cds or photos or a lot of music the larger drives are required. If your hard drive starts to get full (running out of storage room) it tends to get slower. This is partly a function of two things. Fragmented files get worse the more full your hard drive is and it takes longer to load files and programs. Second the operating system creates a file called a swap file which is used when the operating system runs out of Ram. It "swaps" something in ram to the hard drive so that it can read something else. If you have no room there for this swap file to expand and contract (windows) or to accomodate the preset amount your system tends to crash or get very very slow.
The problem is to determine which is which without being a technician. If You open My Computer (windows) and right click on the C: drive it will show you a pie chart of how full your drive is (ps note that a 40 gb hard drive will not say exactly 40 Gb some will say slightly more but most will say slightly less depending on brand) and divide it into used space (usually blue) and free or unused space (usually Pink). If your pie chart is mostly blue you need a larger hard drive. If it is mostly pink you don't. Chances are yours is mostly blue. The company you are dealing with seems (by your question) to be reputable and most shops reputable or not would be foolish to lie about something as easily checked as that. If it was an issue of how your hard drive is working then you have to rely on the shop's judgement or get a second, third or fourth opiinion and if all agree take it back to the first place. The next question is how big? I'm not sure you need a 120 Gb hard drive but it may be cheaper than a new smaller size hard drive. Notebook hard drives are usually made in a smaller variety than desktop hard drives because they must be smaller and are relatively expensive to manufacture as compared to desktop drives. 120 Gb is a good size, but if you are doing a lot of video, music and pictures it too can fill fast.
Because a computer is a "system" you may and probably will gain speed when you upgrade ram or when you get a bigger hard drive. Unless you are pushing the limits of your system (full hard drive and maximum ram) you probably won't gain a lot of speed..
What they are saying is probably true and as I say it can be checked easily. With the disk duplication programs like Norton Ghost they can copy or "clone" your disk. Just make sure they Clear your old disk before you leave.
Hope this helps.
Tekkiefrst