What is the difference between cache and ram?



Posted by captain-kirk (183) on 07/03/99 at 05:13:08 PDT

RAM is general purpose memory, used to store programs, data, graphics, etc. You want 64meg or so these days.

Cache is specialized memory used by the CPU to speed up access to the RAM. It acts as a buffer, "looking ahead" and trying to anticipate the next item needed from RAM. When it guesses right, the CPU keeps on running, full speed ahead. When it guesses wrong, then the whole machine stops and waits while the right data is found and brought to the CPU. 512K is a decent amount of cache these days; avoid machines with zero cache (e.g., the early Celerons).

One twist on the cache front is that the CPUs also have cache embedded right on the chip itself; these cache amounts are generally in the 16K - 64K range. This cache is called L1 (Level 1) cache, as opposed to the cache mentioned above (L2). Hope this helps...the cache issue, in particular, can be tricky... When talking about browsers and cache, the cache here is actually harddisk space used by the browser to store recently-used web pages. The idea is similar to the CPU cache in my last post; the idea being when you surf, you are more likely to use a web page that you've looked at in the past than you are to find a new page, so it stores them on disk, which is a lot faster to retrieve from than constantly resending the page over the net.

The tricky thing about this kind of cache is that the web page might have changed. Your browser preferences determine how often the browser checks to see if it has changed. Mine is set to "once per session"; I assume in the typical 30 minutes that I'm on that the web page has not changed. If you are using volatile pages, or stay on for hours and hours, you may want a different setting.

Pushing the 'reload' button, by the way, forces a refresh of the web page, so that if you are watching an auction, say, if you use this button, you will always get the latest page.

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