WEBVTT

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 One of the things that the Cisco Certified
 Technician Exam expects you

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 to understand is the terminology used
 to explain the different kinds of

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 memory that's common in
 routers and switches.

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 And that's what I'm going
 to discuss in this video.

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 I am Keith Bogart and I will be
 your instructor for this video.

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 So this video as far as terminology is
 concerned because that's what we're

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 looking for. I'm going to make sure
 that by the time we're done here you

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 understand the terminology of four
 different kinds of memory.

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 Specifically I'm going to talk about
 ROM, DRAM, NV RAM, and FLASH.

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 So let's start with ROM.

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 The word ROM is an acronym which
 stands for read only memory.

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 It's also sometimes called EEPROM which
 is electrically programmable read

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 only memory. So ROM is most often
 on its own separate ship.

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 Like for example here we see an image
 of a Cisco 7200 series router, the

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 motherboard or the control board and
 we can see that the boot ROM is its

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 own separate ship here in
 the upper right corner.

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 So what's the ROM used for?

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 Well for one thing it contains the ROM
 monitor which is a software diagnostic

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 program you can do problems with the
 router or switch if it has problems

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 loading up when it
 first turned on.

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 It also has the boot loader or helper
 which is a small program used to

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 help load the Cisco iOS image.

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 It also contains some small software
 programs for the post, the power

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 on self diagnostic programs which do things
 like check other memory locations,

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 checks to see what line cards or modules
 are in the system and if they're

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 operating and plugged
 in correctly.

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 And sometimes depending on the system
 you're on the ROM might actually

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 contain the full iOS
 image as well.

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 Another type of memory you need to
 be familiar with is dynamic random

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 access memory. This is typically contained
 on DIMMs or dual inline memory

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 modules. So one of the things that makes
 DRAM memory unique is that based

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 on the structure of this contents while
 the router or switch is actually

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 powered on while it's turned on.

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 Now there's two different kinds of
 DRAM memory and I want to make sure

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 you're familiar with this.

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 I should say DRAM memory itself is divided
 into two different purposes.

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 The memory itself is still physically
 the same kind of chip but DRAM memory

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 can be used for either primary memory
 which is also sometimes called main

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 or processor memory as well as shared
 memory which is also called packet

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 or input output memory.

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 What's the difference?

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 Well if a section of my DRAM chip, my
 DIMM is being used for my primary

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 memory, this is where things
 like your tables are stored.

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 For example your OSPF database, your
 ARP table, all the tables that the

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 CPU would need to access, all the memory
 where the CPU would load is various

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 software functions and software programs
 would go into primary memory.

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 Now there's another section of DRAM memory
 which is used to actually hold

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 the packets or the frames and this is
 our shared memory also called our

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 packet or input output memory.

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 So if we talk about our interface queues,
 our interface buffers, that

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 goes in the section of DRAM memory
 which is our shared memory.

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 So what is DRAM actually used for?


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 Well it's used for a lot of critical
 things in your router switch.

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 So anytime you can think of a section of
 memory that's going to hold something

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 that's going to change on a fairly frequent
 basis, that is typically your

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 DRAM memory that's being
 used for that.

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 So for example your routing tables,
 your ARP tables, your MAC address

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 tables on your switches is going to
 be used, DRAM memory is going to be

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 used for that. Your interface buffers
 and queues, those are changing all

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 the time, DRAM memory is
 being used for that.

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 As well as your device configuration
 information that's used at runtime,

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 your running configuration
 is stored in DRAM memory.

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 As well as your iOS software, now this
 might be a little misleading but

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 think about this, when the device, the
 router switch is powered off, is

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 turned off, your iOS software is not in
 DRAM because remember when something's

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 turned off, DRAM memory
 is not in use.

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 DRAM memory is emptied when the device
 is in a powered off state.

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 So something else, some other kind
 of memory that we're going to look

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 at in just a moment is being used for
 long term storage of your software,

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 of your iOS image.

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 And that's typically storing that iOS
 image in a compressed or zipped

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 state. Now once you power on or turn
 on your router or your switch, then

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 that iOS software is taken out of that memory
 that we'll talk about uncompressed

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 or decompressed and loaded
 into DRAM memory.

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 Now the type of software we should be
 familiar with is something called

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 nonvolatile random access memory.

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 Now DRAM was dynamic random access
 memory because it was dynamic, that

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 meant it lost its contents
 if you turn the device off.

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 If power wasn't consistently supplied
 to it, DRAM memory was erased.

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 NV RAM is battery backed static RAM
 which means its contents are saved

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 even upon the loss of power.

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 So what's stored in NV RAM?

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 Well that's where your permanent configuration,
 your saved configuration

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 otherwise known as your startup
 configuration file is located.

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 It's also a permanent storage place of your
 hardware revision and identification

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 information as well as your
 configuration register.

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 I'll talk more about the configuration
 register and what you can do with

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 that in a subsequent video.

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 And the last piece of memory that you
 need to be familiar with as far

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 as its terminology is something
 called flash memory.

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 This is also like ROM in the fact that
 flash memory retains its contents

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 even upon a loss of power.

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 But unlike ROM, flash memory is erasable
 and reprogrammable up to about

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 a hundred thousand times or so.

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 And no battery backup is required.


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 So flash memory is typically where you
 would have your long term storage

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 of your Cisco iOS software.

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 And flash memory can either be on an
 internal chip or an internal SIM

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 or dim within the device
 or like we see here.

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 It could also come in the flavor of
 something called a compact flashcard

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 which you could remove
 and then take with you.