Types of RAM

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Time
12 hours 9 minutes
Difficulty
Beginner
CEU/CPE
12
Video Transcription
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>> Hi and welcome to the CompTia A+ 220-1001 Module 2.
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This is Lesson 3.2, Types of RAM.
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We're going to talk about the types of RAM
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used in common motherboards.
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I'm your instructor Bill Price.
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Let's look at our lesson objectives.
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First we're going to talk about, what is RAM?
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Random Access Memory.
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Then we're going to talk about DIMM,
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Dual Inline Memory Modules,
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SO-DIMM, Small Outline Dual Inline Memory Modules.
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What is DRAM or DRAM?
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Dynamic Random Access Memory.
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What is SDRAM?
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Synchronous Dynamic Random Access Memory.
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Finally, we're going to talk about what is DDR?
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Double Data Rate. DDR2,
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DDR3, and DDR4.
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You may remember this from an earlier lesson,
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but we're going to go into more detail.
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Let's go and get started. What is RAM?
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Random Access Memory.
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Think of memory or RAM as
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your system's short-term data storage.
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In a very early lesson,
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we learned that your system at
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its basic level outputs information that was put into it.
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That data or information is retrieved from
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your hard drive storage or wherever it's
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stored for long-term storage and loaded into RAM
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while you're working on it then
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returned once you're done with it.
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While that data is being processed or
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used it's temporarily stored in RAM.
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RAM or Random Access Memory is the place where data
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resides while you're working on
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it or when your program is using it.
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Again, we talked about briefly,
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when you're working on
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a spreadsheet or a document or something like that,
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while it's active and you're working on it,
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all of that is being done in your RAM.
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When you're done with it and you save
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it and you close it up,
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that goes right back to your permanent storage
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or your long-term storage,
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which may be your hard drive or whatever type
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of storage device that you have to
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store things for long term.
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The process of transferring all the data back and
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forth from memory happens all the time in your system.
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The faster your system can perform these transactions,
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the better the overall experience is.
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When asked about how much memory does your system have,
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this is the memory that is being referred to,
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it's not how large your storage or hard drive device is,
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it's how much memory you have in your system.
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If your system has low memory,
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applications will take longer
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to retrieve and be processed,
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and put back in memory.
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We've all experienced that
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before when you have low memory,
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it's a long wait while things are
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being processed and being retrieved.
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Let's first start talking about DIMM,
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the Dual Inline Memory Module
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since these were the older modules.
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A DIMM, Dual Inline Memory Module is
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a model that contains
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one or several Random Access Memory,
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RAM chips on a small circuit board with
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pins that connect it to the computer motherboard.
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Each side of the DIMM has
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modules on it that are connected together.
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They are separate though.
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DIMMs have a 64-bit data width
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which gives them the capability to transfer
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data from these memory modules
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in the 64-bit data blocks at a time.
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Moving on to SO-DIMM,
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Small Outline Dual Inline Memory Module.
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Standard DIMM is in the form of a rectangular stake,
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approximately 5.5 inches in length.
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The small outline Dual Inline Memory Module
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or the SO-DIMM is about the half the size of that.
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It's about 2.7 inches long.
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Both types of DIMMs are most commonly
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at most 1.2 inches tall.
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SO-DIMMs are mainly used in
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portable computing devices such as laptops and tablets.
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This is your smaller modules
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that will be in those portable devices.
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Let's look at the DIMM,
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Small Outline Dual Inline Memory Modules
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, the SO-DIMMs.
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As you just see, we have them
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laid out here and you can see
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the various characteristics
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>> of these different versions.
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>> There is one characteristic
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that you can see straight off from looking at these,
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is that the notches are in
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different places depending on
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>> the version of the SO-DIMM.
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>> If we first look at the DDR 200 pins SO-DIMM module,
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you can see that the notch at the bottom along
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the line of pins are
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towards the right-hand side of the module.
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If we go down to the next DIMM,
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the DDR2 240 pins,
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the notch is pretty much almost relativity
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same area down to
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the DDR3 200 pin
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that notch has moved totally over to the left-hand side.
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Finally, the DDR4 260 pin is
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back over more almost
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on the center but towards the right again.
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This basically shows you that
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these memory modules are not backwards compatible.
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You will not be able to take
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a DDR 20 pin memory module and put that into
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a newer mobile device
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that's requiring a DDR4 260 pin module.
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The pins would not line up,
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the modules will not line up, therefore,
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you will not be able to fit the RAM.
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What is DRAM?
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Dynamic Random Access Memory.
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In Dynamic Random Access Memory,
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random means that the information in memory can be
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accessed anytime in the memory module at any place.
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Data is not retrieved in a sequential process.
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It can be retrieved randomly.
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Any address of data is used to get the data.
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The word dynamic means that memory has to be refreshed.
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While your system is powered on and running,
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thousands of refreshes happen to
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your DRAM to retain the data that it's holding.
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Once the power is removed and turned off,
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data is released back to memory.
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That shows you or you probably
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have that experience before where if you're
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working on something and
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the computer randomly shuts down or turns off,
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that's returned back to
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memory and your information is lost.
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What is SDRAM?
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Synchronous Dynamic Random Access Memory.
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DRAM is asynchronous.
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This was a problem with gathering
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data as it came in so it
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could be queued for process that it was working with.
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Because DRAM was asynchronous,
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it was not going to work with fast processors.
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As technologies got faster and faster,
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this was a bottleneck more or less,
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trying to gather this data
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when it was an asynchronous process.
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Then we came along with SDRAM or
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Synchronous Dynamic Random Access Memory.
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It's the type of DRAM that is synchronized with
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the processor system bus for speed advantage.
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Since DRAM is synchronous and therefore relies
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on a clock to synchronize signals,
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creating predictable orderly cycles
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of data fetches and writes.
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However, SDRAM transfers data on the edge of the clock,
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and we're going to look at that a little bit further,
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give you further more understanding.
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In this diagram, we have the clock cycle,
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and you can see at the top in blue we have the SDRAM.
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That's where it syncs
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the gathering of the data on the top of the clock cycle.
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Now, DDR SDRAM means that this type of
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SDRAM fetches on both the leading
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and the falling edge of
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the clock symbol that it regulates.
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That's going to lead us into
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another discussion talking about DDR.
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What is DDR?
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DDR is the Double Data Rate,
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transfers of data on both the rising and
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the falling of the clock cycles or twice per cycle.
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Again, if we go back to the previous slide,
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if you look at the SDRAM,
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it cycles the data just on
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the upside or the one side of the clock at the top.
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But the DDR,
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it cycles it both on the up and the bottom.
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The DDR, the Double Data Rate transfers
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data on both the rising and
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the falling of the clock signal of twice per cycle.
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Makes higher transfer rates possible due to
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its efficient and strict control of
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data timing and clock signals.
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It's not backward compatible or forward compatible.
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DDR3 will not fit in a motherboard rated for DDR2.
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We have some of the transfer rates listed here below,
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the DDR transfer rate is 1,600 million bits per second,
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DDR2 2,133, DDR3 2,666, and DDR4 3,200.
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We've covered a lot of information about RAM.
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We talked about what is RAM?
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Random Access Memory.
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We followed that,
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went into the DIMM,
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the D-I-M-M, the Dual Inline Memory Modules.
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Then we talked a little bit more in
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detail about this SO-DIMMs,
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the Small Outline Dual Inline Memory Modules.
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Then we had a discussion on the DRAM,
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the Dynamic Random Access Memory,
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followed by SDRAM,
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Synchronous Dynamic Random Access Memory,
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and we finished that off with the DDR,
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the Double Data Rate, DDR2,
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DDR3, and DDR4.
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That is it for this lesson.
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We're going to be talking about
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RAM in our future lessons.
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Until then, we will see you in the next lesson.
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