Computers 101: RAM

RAM or Random Access Memory, is one form of data storage in a computer.  In fact it is the most common memory found in computer as well as other devices such as printers and fax machines.  The random part comes from the fact that the memory can be accessed randomly, meaning that each individual byte can be accessed without having to go through the bytes before it.

There are two basic types of RAM.  You have the common DRAM (Dynamic RAM) and the less common SRAM (Static RAM).  Both are volatile, and if you've been reading the previous posts, we know what volatile means when the power goes out, the memory is cleared.  SRAM is much less volatile than DRAM due to the fact that it doesn't need to be refreshed as often but does use much more power.  Other than that, the major differences between the two types is speed and price.  SRAM is much faster than DRAM in terms of how quickly it can be accessed.  With that increased speed comes an increased price that has priced itself out of the market in the common PC, at least in terms of being the main memory of the computer.  SRAM is used as the cache memory in the processor and motherboard due to it's faster access times.  SRAM is also seen routers, printers, CD and DVD players, and digital cameras.  You'll also find SRAM on hard drives as the disk cache.  We'll delve into this more when covering hard drives next week. 

The type of RAM that we'll spend the largest about of time covering here is DRAM.  The reason why is because it is the most common found inside our computers, being the main memory.  What the main memory means is that it is accessed by computer programs to run their operations.  The reason why DRAM costs less than SRAM to make is because it is much simpler in it's design.  While SRAM uses 6 transistors per bit, DRAM only uses 1 transistor and capacitor per bit.  This allows DRAM to be very high density and fit millions of these transistors and capacitors on a chip. 

RAM is mounted on a blank memory module for it to be used in a motherboard.   If you look at the first picture in this post, you'll see the black boxes on the green board.  The black boxes are the actual RAM themselves.  They are then put onto the blank memory module or printed circuit board (same stuff as the motherboard if you remember). 

There are and have been many different types of DRAM.  You have FPM (fast page mode dram), EDO (extended data output), BEDO (burst EDO), SDRAM (synchronous DRAM), SLDRAM (synchronous link DRAM), ESDRAM (enhanced SDRAM), and DDR (double data rate SDRAM) to name a few.

Likewise, there are many types of memory modules for the different types of DRAM to be mounted on.  You have SIPP (Single In-line Pin Package), dual in-line package, TransFlash Memory Module, SIMM (single inline memory module), and DIMM (dual inline memory module).  We'll focus on the DIMM memory module.

Lastly, there are many different types of DIMMs, each with different pin counts.  Everything ranging from 72-pin SO-DIMM to the 240 pin DIMM used for DDR2 and DDR3 SDRAM.  The later is the current standard for RAM being used in PCs today. 

DDR SDRAM (Double Data Rate synchronous dynamic random access memory) was a big break through in the world of RAM.  DDR was able to offer twice the amount of data transferred compared to the older SDRAM.  Since then we've been able to have DDR2 SDRAM and DDR3 SDRAM, each of them offering faster speeds with lower power consumption. 

Prior to SDRAM, RAM speed was measured in nanoseconds.  The faster the RAM, the less time it would take to fetch data.  With DDR-SDRAM, the speed is measured in megahertz (Mhz).  While the higher the Mhz = the faster the RAM, your FSB (front side bus) also factors into the speed of the RAM and how it affects your computer.  I'm not going to get into the specifics here about RAM timings and speeds here as this post is already getting too long for a general overview but look for some more info on it in future posts.

There are some new technologies coming around that may supplant the DRAM technology that currently sets our standard for RAM.  As nanotechnology gets more and more advanced, breakthroughs are expected to push our computing standards.  This is a good thing so that we don't hit a memory wall in computing.  The memory wall is the growing difference between CPU speeds and memory speeds.  A quote from Intel on the mater.

  "“First of all, as chip geometries shrink and clock frequencies rise, the transistor leakage current increases, leading to excess power consumption and heat... Secondly, the advantages of higher clock speeds are in part negated by memory latency, since memory access times have not been able to keep pace with increasing clock frequencies. Third, for certain applications, traditional serial architectures are becoming less efficient as processors get faster (due to the so-called Von Neumann bottleneck), further undercutting any gains that frequency increases might otherwise buy. In addition, partly due to limitations in the means of producing inductance within solid state devices, resistance-capacitance (RC) delays in signal transmission are growing as feature sizes shrink, imposing an additional bottleneck that frequency increases don't address.”

CPUs will be useless as the RAM can't keep up.  Hopefully the powers that be will remedy this for us in the near future.

Well that basically wraps up the RAM basics so far.  I'll offer this disclaimer on each of the posts in this Computers 101 session, that there is much more information out there on RAM that can be covered and we may get there eventually in this blog.  If you do have further questions, feel free to message me and I'll get back to you ASAP.  Thank for reading and hope to hear from you.