Ep 20 RAM
18th July 2008
What is RAM?
RAM or Random Access Memory is the “scratch pad” of the computer. It is the middleman for the slower components of the computer (like the hard drive) and the CPU. Data is loaded into the RAM that the CPU will use. It also provides a place for information to be stored from the CPU. It is like a personal assistant for the CEO/CPU.
What is the job of RAM?
Memory stores three basic things:
- The Operating System (OS) and other system software the computer needs to work
- Applications programs that are working on specific tasks (Word Processing, Solitaire)
- The Data that is being processed by the application
Random vs. Serial
RAM is an abbreviation for Random Access Memory, but what does the Random mean?
Imagine if you wanted to play your favorite song; it was song 3 on side A on a tape. You would have to fast forward or rewind through the other songs before you could get to that song. This type of data accessing is called Serial. Step 1, Step 2, Step 3, Step 4, etc….
Zooming to the modern age were tapes and tape decks have become ancient technology, we have the MP3 player. If you want to access a song or podcast on your iPod or other MP3 player you can directly access it. Being able to go to any spot without having to go through step 1, step 2 step 3, etc… Random access means that any individual byte of memory can be accessed at any time. All parts of memory are equally accessible.
Classes of RAM
When we start to get into the types of RAM, the aspiring tech can get a little confused. We are going to start with the two families of RAM:
- Static
- Dynamic
Static RAM (SRAM)
This type of RAM is incredibly fast. It is fast because it uses several transistors to hold each bit of data in memory. More importantly then that is that the data stored in this type of RAM will not decay for as long as the power is on. The more geeky explanation is that SRAM does not need to be refreshed.
Quick word about refreshing- Refreshing means the data must be re-energized. Data in Dynamic RAM will decay, fade away, disappear, or what ever you want to call it. The data must therefore be re-zapped in order to keep if there. While the computer is refreshing this data it cannot be used. For those of you who like hockey, think when the ice has to be refreshed by the Zamboni, for those of you who do not like hockey, sorry. While the Zamboni is on the ice the hockey players cannot play. They have to wait till the ice is done being refreshed.
Static RAM is supper fast because it does not need to be refreshed, therefor it does not have to wait to be used. This might sound great, but there is a prices pay for this constant state of freshness. Static RAM is boo koo expensive. Because of how expensive SRAM is, you can only find it as part of the CPU cache.
Dynamic RAM (DRAM)
This is the type of RAM that you can install and upgrade in computer. There are many different variations of DRAM but they all share a common characteristic, they must be refreshed.
To quickly recap. There are two main categories of RAM. Static and Dynamic.
DRAM a Closer Look
Dynamic RAM has two children. Each child grew up and had families of their own. Lets take a look at DRAM
Asynchronous DRAM
This was the very first type of RAM used in computers. It is not on the A+ exam or relevant in today’s world. Know this one thing about Asynchronous DRAM: it was asynchronous. It did not keep up with the CPU. RAM would receive operating instructions, work on it, then reply when it was ready.
So if Asynchronous RAM was a type of communication it would be a discussion board. Post your thought, idea, flame, and then wait for someone to reply back to it.
Some names used in the old days were (if you see any of these as an answer choice on the A+ exam, you can gaurnetee it is NOT the right answer):
- Fast Page Mode (FPM)
- Extended Data Out (EDO)
- Burst Extended Data Out (BEDO).
Synchronous DRAM (SDRAM)
This is the second child born to DRAM. This child was smarter, more hansom and just plane better. Say hello to Synchronous RAM. If Asynchronous was posting to a discussion board, then Synchronous was like talking on Skype. Two way, real time communication.
Types of SDRAM
The first types of SDRAM were named after their bus speed.
Older Types of SDRAM
This RAM is named accordingly to the bus speed, PC66, PC100, PC133. They all used a 168-pin DIMM connection. DIMM stands for Dual Inline Memory Module, it means that each side sends different information then the other side.
- JEDEC SDRAM
- Ordinary SDRAM
- Also known as JEDEC SDRAM, PC66
- PC 100 SDRAM
- Rated to use 100 MHz FSB
- PC 133 SDRAM
- Rated to use 133 MHz FSB
- Should be compatible for machine that need PC66 and PC 100
New SDRAM Technology
- DDR SDRAM
- DDR stands for Double Data Rate.
- The old SDRAM could only read/write once a cycle, the double data rate could read/write twice per cycle.
- SDRAM used to be measured by their bus speed the newer DDR was measured by the Bandwidth/Throughput.
- DDR can give 64 bits/8 bytes of information in one shot.
- Take the 64 bits times the amount of information that can be access per second. This lets us know how fast the RAM is.
- For example: DDR200 chips can transfer 8 bytes of information 200 million times per second, so it is called PC 1600. 8 x 200 = 1600
- For the A+ exam you must understand and be able to take one piece of information like the PC speed rating and covert it to the DDR Speed rating. Or vice versa. Do not memorize the chart but understand how they get the numbers.
- DDR stands for Double Data Rate.
- DDR II SDRAM
- Has the following befits over DDR:
- Increased Performance
- Increased Bandwidth
- Reduced Cost
- Lower Power Consuming (Good for laptops)
- Improved packaging
- 240-pins Connection
- DDR uses 184-pins
- Notches are slightly different
- Prevents the installation of DDR2 in a DDR machine
- 240-pins Connection
- Has the following befits over DDR:
- DDR3 SDRAM
- 30% reduction in power consumption compared to DDR2
- Higher bandwidth
- Uses 240-pins (like DDR2)
- DDR2 and DDR3 are the same size but have different notch location (prevents putting the wrong stick in the computer)
- Rambus DRAM
- Got its name from its creator Rambus Inc.
- Uses a proprietary dual-channel technology
- Very good performance but typical more expensive
- Found in Pentium 3 and early Pentium 4 computers
- Never found in AMD systems!
- Rambus Sticks
- A stick of Rambus is called a RIMM
- RIMM does not officially stand for anything
- Comes in 84pin, 168pin, & 242pin
- A stick of Rambus is called a RIMM
Find the Right RAM
What you do not know can really, really cost you money. Not that long ago I was looking for a memory upgrade for my MacBook Pro. Through the Apple store it was going to cost me about $1,000 to max out my laptop. I went looking else were and found the memory I needed for about $100. Wow, that is just a slight difference.
There are three places I recommend to get your RAM. None of them sponsor me. Crucial.com, and Kingston.com have great website that will walk you through the process of finding the type of RAM you need. Both manufactures are trusted names in RAM. I also like to use Newegg.com. Some of Newegg’s RAM is brands I have never heard about, but they have a great customer rating tool that can really help you choose the right RAM for you.
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