You can think of the RAM in the computer as working memory. The programs and any data that is required to be kept permanently (that best selling novel, etc) is stored on disk. Stuff is read from disk into RAM as needed
(the processor can only directly access RAM).
Pretty much the way I pictured things. Can you explain this processor access? Which processor?
DRAM is used for large amounts of memory - the gigabytes of memory in your PC - because it is cheap. It is cheap because each memory cell (1 bit) only requires a single transistor. Therefore, you can get more bytes on a given silicon area. It has the disadvantage, as danhanegan notes, of needing to be continually refreshed (every few milliseconds) which means it always consumes power, even if you are not accessing it.
So, power is not constantly used to maintain dRAM memory, just has to be made available rather frequently (refreshed?), to keep data from "dying out"?
There isn't really a way of deleting the content of RAM while the computer is running - because the code the computer is running is in RAM (the operating system, any applications and data) you would crash the machine if you tried to change it. But the data will disappear within milliseconds of power being removed.
This, the, accounts for the time used after turning PC "on", as the operating program is drawn from H.D. and placed in RAM?
SRAM will store data without it being refreshed as long as power is supplied (sorry danhanegan

). However, it can do this because it uses 4 or 6 transistors for each bit which makes it much more expensive. (Silicon chip pricing is primarily determined by (a) chip size and (b) number of units sold.) However, it has the advantages of being faster to access and only using (significant) power when it is accessed. It is therefore used for on-chip memory, caches, etc.
Seen frequently, "cache", "cached", what exactly is meant? The traditional meaning, such as something stored away, or "hidden"?
Then there is non-volatile memory (such as flash). This will retain data even when the power is turned off. It is used for mobile devices and increasingly, again as danhanegan said, for solid state "disk drives" (with no disk!). These also only use 1 transistor per bit (nowadays, they might store 2 or 4 bits per transistor). But the transistors are slightly larger then DRAM and the market is not so big so they are still more expensive. But they are becoming more and more widely used.
Again, by what physical means are these things able to retain memory without back-up power? As I understand it, the H.D. still requires back-up power, either from being plugged in, or a back-up battery in the box somewhere? When I studied digital computers in their infancy, the state of the art was supposedly a new development called "bubble memory", which I believe required no back-up power, could be wrong, though. Over the years, I have never heard the term bubble memory again. Probably was a fluke.
Temporary Internet files are a temporary (really?) store of stuff you have accessed from the web - copies of web pages, images, etc. They are stored on disk when you access a web site so that when you go back to that web site, you computer can access these local copies instead of downloading it all from the web again (it checks the date of the web site against the files to see if it needs to download a new version of the page). This speeds up your browser.
Does this imply that every page accessed is stored forever on H.D.? Seems impossible, given the amount of data. If so, are settings available to allow user to use RAM exclusively for storage of browsed info?