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- [Instructor] Let's talk
about Magnetic Hard Drives.

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The hard disk drive
implies a magnetic disc.

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HDD or hard disk drive
when we hear these terms,

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we're talking about magnetic disks

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and standard magnetic hard disks

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are three and a half inches wide,

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they go in a standard bay
in your desktop computer

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and they use multiple
platters to store data.

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So here's an example of a hard drive,

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this is an illustration of a hard drive

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with the top taken off and
here we have the platters,

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they rotate around a spindle,
which keeps them in place

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and we have read/write heads
for each of the platters

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on the end of an actuator arm

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which moves across the platter
to read the information

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from the appropriate sector and track.

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So we have some moving parts here

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and the moving parts can fail over time,

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so that's one of the reasons

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for the move to solid state drives.

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And over here, we have our
power and data connectors

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and optional jumper block which will show

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on a real hard drive in just a little bit.

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So that's some of the parts
there of the hard drive,

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the internal workings of the hard drive.

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Are you ever gonna fix these?

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No, does the A+ exam
expect you to fix these?

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No, but it's good to know
how the hard drive works

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so you have an idea of
what could possibly fail,

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the read/write head might
fail, or the arm might fail

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and you might hear some
noise in the hard drive,

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excessive noise which means

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that the hard drive's about to go so,

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you know, you wanna watch for that.

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These drives are usually
SATA, so serial ATA

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and they make use of a
15-pin power connector

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and the 15-pin power
connector has a vertical tab

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on the right usually
and it makes it easier

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for orientation when you're
connecting that power cable,

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and the power supply sends
3.3 volts, five volts,

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and 12 volts to that SATA drive

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and those are the orange and red

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and yellow wires respectively.

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And you also have your data cable here,

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the data cable is a seven-pin connector

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and that connects here.

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And let's go ahead and show
that on a real drive right now.

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Here we have a Western
Digital 500 gigabyte drive,

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it's standing on its ends

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and here are the connectors
that we spoke of.

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This is the SATA power connector

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and that port has 15 pins
you can even count them here.

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And here is the seven-pin data connector,

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again, you can actually count these pins

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so you know which are which.

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That power connector, as we mentioned,

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has a little tab here on the right

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and that helps you to
orient the power connector,

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the data connector has a
little tab on the left,

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so that's just for orientation.

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And here we have the jumper block,

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and that's really only used
if you're gonna use this drive

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in conjunction with older IDE drives,

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which I don't really recommend

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and some other special circumstances,

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but you're rarely gonna use that or see it

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on today's SATA drives.

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Here we have a circuit board

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and that contains the controller chip

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and the cache memory for the hard drive

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and it has a flex circuit which connects

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to the spindle here, which
the platters rotate around

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so we can have this
communication for the hard drive.

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So remember, there's moving parts in here,

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and we have a lot of
things going on that SSDs

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or solid state drives
pretty much alleviate

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any of these problems that you'll have

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in a hard disk drive such as this.

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So remember that magnetic
hard disk drives,

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they're still out there,
you'll still find 'em,

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but they're quickly being overshadowed

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and overtaken by the solid state drive.

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Let's talk a little bit about
hard disk specifications.

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There's a couple you need
to know or several really,

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and the first is capacity.

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The capacity is the amount of data

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that the hard drive can hold.

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And so, for example, you might
have a 500 gigabyte drive

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or you might have a one terabyte drive.

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And the capacity is important,

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you want to know, you know,

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how much data are you gonna be storing?

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You wanna understand how much
data your drive can hold,

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and, you know, keep in mind,

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you may need a bigger drive later on,

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or an array of drives or a good
backup system or something.

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So, keep in mind the capacity,

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also, when you're
dealing with hard drives,

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when you look at the
manufacturer's website,

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say Western Digital or Seagate,

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you'll see the drive marketed
as say, 500 gigabytes,

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but when you look at that
drive in, say Windows 7,

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you'll see it as 465 gigabytes

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and you're not losing any data,

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you're not losing any capacity.

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The reason for that is because
the hard drive manufacturer

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uses the base-10 system

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and Windows uses the base-2 system

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where a kilobyte is 1,024
bites instead of 1000

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and a megabyte is 1,024
kilobytes and so on

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and so in total, a 500
gigabyte drive will be read

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by say Windows 7 as 465
gigabytes, so that's capacity.

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Next is cache.

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Cache is a buffer of memory

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and the cache on most hard
drives is on-board DRAM,

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it's right on the circuit
board to the drive.

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And you can compare this with CPUs,

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CPUs have cache memory
which we've spoken of,

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and they use SRAM and that's
significantly faster than DRAM,

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but, like the CPUs, the hard drives cache

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helps to access frequently
used information

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faster than if it were to get
it from the magnetic disc,

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in fact, a lot faster,
you know, your on-board

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DRAM's gonna be much faster
than the magnetic disk.

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So there's capacity and cache,

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let's look at our hard
drive again and show those

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on the label of the drive
and show what they mean.

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Okay, here we're looking
at the top of the drive

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and we're looking at the label,

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we see this as a Western
Digital 500 gigabyte

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Caviar Blue drive, just the basic drive

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for holding basic data.

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But we also see here that it says SATA

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so we know the type of drive,
and it says 16 megabytes

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of cache, so we know how much
cache memory this drive has.

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Newer drives today have a lot
more cache and faster cache.

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We also see here the
model number, WD5000AAKS.

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Now it's important to know the cache

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and the model number, and perhaps even

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the serial number here, whenever
you are replacing a drive

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because you should replace the drive

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with the same drive usually
unless you're upgrading,

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but also if you're gonna
create an array of drives

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say a RAID 1 or a RAID 5
array, or any type of array.

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You wanna use the same type of drive

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for all the drives in the array

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and you really wanna
go by this model number

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when you do that.

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So make sure that all the
drives are WD5000AAKS,

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because the model names
can be slightly different,

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like AAVS or WD5000ABKS, or what have you.

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So you wanna be real careful
with that and check that

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make sure that you're
using the correct drive,

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using the same drives for
all of them within the array.

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We also have a schematic
of the connections

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showing you where to connect
the power and the data

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and so on and if you
have to make any changes

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to the jumper settings,

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it gives you that information there.

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So always look at the label,
the drive it can give you a lot

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of information that you need
to know as far as connecting it

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or compatibility or exactly
what type of drive it is

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if you can't find this
information within your bios

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or within your analysis software.

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Okay, getting back to
hard disk specifications,

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let's talk about data transfer rate.

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The data transfer rate of a hard drive

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is the maximum amount of bytes
that can be sent or received.

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But it's a theoretical maximum
and the theoretical numbers

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are never really actually achieved,

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generally, you'll get a
data throughput amount

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that you actually are using,

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but, you should know the
data transfer rate maximums

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for SATA and you can see
those are listed here.

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First, we have SATA Revision 1.0

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and we see that it's
measured in bits and bytes,

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so 1.5 gigabits per second will basically

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come down to being 150 megabytes

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of data being written
to the drive per second.

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Now you may say, well, why
didn't we just divide by eight?

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And the reason that it's
only a 10th of the data

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sent serially is because of encoding.

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You have some additional encoding data

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that has to be removed
after it gets to the drive

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before that data can be
written to the drive.

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So you lose a little bit there,

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so 1.5 gigabit serial connections

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will actually store 150
megabytes of data per second

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on the drive.

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Then we have SATA Revision 2

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and you'll see a lot of
these drives out there,

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there are three gigabytes per second

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and they can write a maximum
of 300 megabytes per second

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to the drive.

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Now, our drive is an
SATA Revision 2.0 drive,

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so it has this theoretical
maximum of 300 megabytes

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per second, but this particular drive

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can only sustain in the
neighborhood of say 120,

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130 megabytes per second

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and this is also referred
to as data throughput,

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the actual amount of data
that you can send back

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and forth in your computer,
in your environment.

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So, in my environment, in my
lab, that's about what I get

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on this magnetic disk,
120 megabytes per second,

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the theoretical maximum is
300 megabytes per second.

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So, some food for thought there.

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Next, we have SATA Revision 3

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and we have one of those
drives going into our AV editor

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also and that's six gigabytes per second

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or 600 megabytes per second.

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And now we have SATA Revision 3.2

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as of the recording of this
video, that's the latest one

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and that goes at 16 gigabytes per second

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and has less encoding data,

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so we actually get a better ratio

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and it's upwards of 1,969
megabytes per second

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or two gigabytes of data per second,

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so that's a big jump, and
that is data transfer rate.

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Couple other things you should know

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for hard disk specifications;

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the first is rotational speed.

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This only deals with magnetic hard drives

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and some examples are
5400, 7200, or 10,000 RPMs

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or rotations per minute.

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The rotational speed is
something that you might look at

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when you're interested in how
fast the data can be accessed.

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If you need really fast data
access, you wanna higher speed.

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If you don't really care that much,

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if you just have a
computer that's connecting

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to the internet, you might
wanna just go with 5,400 RPM.

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Why?

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'Cause there's a cost factor involved,

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the drives with the higher
RPMs are gonna cost more money.

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But again, the drives with the higher RPMs

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have faster access times

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because there's less seek
time to get the information

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from the particular sector
and track on the drive.

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Now this is tied into
another term called latency.

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After a track has been reached
by the read/write head,

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latency is the delay in time
before a particular sector

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on that platter can be read.

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So that's how long it takes
for the platter to spin around

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for the read/write head
to actually get that data,

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and it's directly related
to that rotational speed.

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It's usually half the time it takes

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for the disk to rotate once.

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So for a very common 7,200 RPM drive,

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the average latency will
be 4.2 milliseconds,

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00:12:54,390 --> 00:12:58,260
but, for a faster drive
that runs a 10,000 RPMs,

250
00:12:58,260 --> 00:13:02,253
it'll be a lower latency, say
around three milliseconds.

251
00:13:03,240 --> 00:13:05,400
So those are some of the
hard dis specifications

252
00:13:05,400 --> 00:13:10,400
you should know, capacity,
cache, data transfer rate,

253
00:13:11,070 --> 00:13:14,130
rotational speed, and latency.

254
00:13:14,130 --> 00:13:17,670
And if you get a chance, get
yourself a magnetic hard disk

255
00:13:17,670 --> 00:13:21,240
and take a look at it,
look at all the ports,

256
00:13:21,240 --> 00:13:23,880
look at the information on the label

257
00:13:23,880 --> 00:13:27,000
and see how it works, connect
it into your computer,

258
00:13:27,000 --> 00:13:29,370
see how the actual drive functions.

259
00:13:29,370 --> 00:13:31,353
So that's about it for this sub lesson.