Cache in your chips and get a bus!

Written by Seamus Dolly

Computer related terminology could sometimes be daunting to newcomers. These are relatively new words or hybrids of words, already in existence. Someone with a degree in English, for example, could not necessarily guess,repparttar function of a particular devise, by its name. This is because such a devise never existed in history or inrepparttar 107775 history ofrepparttar 107776 English language. Tolerance and patience is required. If you work inrepparttar 107777 field of computers, these "new" words must be learned. However, P.C.'s are designed for use by ordinary people, andrepparttar 107778 gritty details regarding their construction, can be largely ignored. A journalist, typist, builder or bookkeeper doesn't need to know what an EIDE or SCSI is, or indeed isn't. Hard drive description is not relevant torepparttar 107779 majority, as long asrepparttar 107780 devise is functional. A "BUS", though, could be guessed by some, as it carries something, not unlike a conventional bus. In this case, it carries current/electrons/data, and is simply a conductor. A bus conductor, if you like. For now, buses are made of copper with experiments underway to utilise other materials. I read recently that "prions", which are a type of protein, are been considered as conductors. Will some of our computers' components be organic? We shall have to see! Fibre optics, which are, basically speaking, glass pipes around four thousands of an inch (0.1 mms.), in diameter, employrepparttar 107781 speed of light, for signal/data transfer. A light (diode), is on or off, at one end, and a photo-resistor atrepparttar 107782 other end registers its state. Now, wasn't that simply put! These glass pipes are coated to reflectrepparttar 107783 light inwards, meaning that light can be "bent" around corners, while within its container/pipe. Heat generation is minimal and electrical resistance is redundant. It is heat generation and resistance that brings your "fan" into play, keeping everything cool, and electron transfer at a controlled level. Low resistance= high current. Your starter motor for your car has really thick cables allowing electrons fromrepparttar 107784 twelve volt power source (battery) to do their job in turning over you engine, which is a considerably difficult task. A smaller cable would have a higher electrical resistance, causing it to overheat, and eventually, melt. Keep listening for that "fan". It is your computers first line of defence. In fact, it isrepparttar 107785 principle of electrical resistance that is employed by electrical heaters.

In Computer Memory what is CAS Latency?

Written by Ron Merts

This isrepparttar question we are asked more than any other question. So, I figured I'd put together a bulletin containing my $0.02 worth!

First of all, what is CAS?

"CAS" is short for "Column Address Strobe". A DRAM memory can be thought of as a matrix, kind of like a spreadsheet with memory cells instead of numbers and formulas. Likerepparttar 107774 spreadsheet, each cell has a row address and a column address (like "AA57" or "R23C34" inrepparttar 107775 spreadsheet). As you might have guessed, there is also a RAS signal, which is shorthand for "Row Address Strobe".

And, what do you mean by "latency"?

Latency refers torepparttar 107776 time that you are waiting to get what you need. Merriam-Webster dictionary defines it as "the interval between stimulus and response".

Now, how does CAS work?

To understand this let's walk through a simplified version of howrepparttar 107777 memory controller actually readsrepparttar 107778 memory. First,repparttar 107779 chip set accessesrepparttar 107780 ROW ofrepparttar 107781 memory matrix by putting an address onrepparttar 107782 memory's address pins and activatingrepparttar 107783 RAS signal. Then, we have to wait a few clock cycles (known as RAS-to-CAS Delay). Then,repparttar 107784 column address is put onrepparttar 107785 address pins, andrepparttar 107786 CAS signal is activated, to accessrepparttar 107787 correct COLUMN ofrepparttar 107788 memory matrix. Then, we wait a few clock cycles -- THIS IS KNOWN AS CAS LATENCY! -- and thenrepparttar 107789 data appears onrepparttar 107790 pins ofrepparttar 107791 RAM. So, for CAS-2 you wait 2 clock cycles and for CAS-3 you wait 3 clock cycles? Bingo!

So, CAS-2 is 33% faster than CAS-3?

Whoa, not so fast! There are a LOT of other factors inrepparttar 107792 memory performance. Here are a few ofrepparttar 107793 main ones: ·Sometimes you have to move to a different row in memory. This means activating RAS, waiting RAS-to-CAS delay, then doingrepparttar 107794 CAS latency thing. ·Other times, you do a "burst" read, when you pull in a lot of data in one big block. In that case, CAS is only activated ONCE, atrepparttar 107795 beginning ofrepparttar 107796 burst. ·Also, don't forgetrepparttar 107797 most important thing: processors have big caches! The cache is whererepparttar 107798 processor stores recently accessed instructions and data. The cache "hit rate", i.e.,repparttar 107799 percentage of timesrepparttar 107800 processor findsrepparttar 107801 information it needs in its own cache, is typically greater than 95%!

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