- [Instructor] Let's talk about Magnetic Hard Drives.
The hard disk drive implies a magnetic disc.
HDD or hard disk drive when we hear these terms,
we're talking about magnetic disks
and standard magnetic hard disks
are three and a half inches wide,
they go in a standard bay in your desktop computer
and they use multiple platters to store data.
So here's an example of a hard drive,
this is an illustration of a hard drive
with the top taken off and here we have the platters,
they rotate around a spindle, which keeps them in place
and we have read/write heads for each of the platters
on the end of an actuator arm
which moves across the platter to read the information
from the appropriate sector and track.
So we have some moving parts here
and the moving parts can fail over time,
so that's one of the reasons
for the move to solid state drives.
And over here, we have our power and data connectors
and optional jumper block which will show
on a real hard drive in just a little bit.
So that's some of the parts there of the hard drive,
the internal workings of the hard drive.
Are you ever gonna fix these?
No, does the A+ exam expect you to fix these?
No, but it's good to know how the hard drive works
so you have an idea of what could possibly fail,
the read/write head might fail, or the arm might fail
and you might hear some noise in the hard drive,
excessive noise which means
that the hard drive's about to go so,
you know, you wanna watch for that.
These drives are usually SATA, so serial ATA
and they make use of a 15-pin power connector
and the 15-pin power connector has a vertical tab
on the right usually and it makes it easier
for orientation when you're connecting that power cable,
and the power supply sends 3.3 volts, five volts,
and 12 volts to that SATA drive
and those are the orange and red
and yellow wires respectively.
And you also have your data cable here,
the data cable is a seven-pin connector
and that connects here.
And let's go ahead and show that on a real drive right now.
Here we have a Western Digital 500 gigabyte drive,
it's standing on its ends
and here are the connectors that we spoke of.
This is the SATA power connector
and that port has 15 pins you can even count them here.
And here is the seven-pin data connector,
again, you can actually count these pins
so you know which are which.
That power connector, as we mentioned,
has a little tab here on the right
and that helps you to orient the power connector,
the data connector has a little tab on the left,
so that's just for orientation.
And here we have the jumper block,
and that's really only used if you're gonna use this drive
in conjunction with older IDE drives,
which I don't really recommend
and some other special circumstances,
but you're rarely gonna use that or see it
on today's SATA drives.
Here we have a circuit board
and that contains the controller chip
and the cache memory for the hard drive
and it has a flex circuit which connects
to the spindle here, which the platters rotate around
so we can have this communication for the hard drive.
So remember, there's moving parts in here,
and we have a lot of things going on that SSDs
or solid state drives pretty much alleviate
any of these problems that you'll have
in a hard disk drive such as this.
So remember that magnetic hard disk drives,
they're still out there, you'll still find 'em,
but they're quickly being overshadowed
and overtaken by the solid state drive.
Let's talk a little bit about hard disk specifications.
There's a couple you need to know or several really,
and the first is capacity.
The capacity is the amount of data
that the hard drive can hold.
And so, for example, you might have a 500 gigabyte drive
or you might have a one terabyte drive.
And the capacity is important,
you want to know, you know,
how much data are you gonna be storing?
You wanna understand how much data your drive can hold,
and, you know, keep in mind,
you may need a bigger drive later on,
or an array of drives or a good backup system or something.
So, keep in mind the capacity,
also, when you're dealing with hard drives,
when you look at the manufacturer's website,
say Western Digital or Seagate,
you'll see the drive marketed as say, 500 gigabytes,
but when you look at that drive in, say Windows 7,
you'll see it as 465 gigabytes
and you're not losing any data,
you're not losing any capacity.
The reason for that is because the hard drive manufacturer
uses the base-10 system
and Windows uses the base-2 system
where a kilobyte is 1,024 bites instead of 1000
and a megabyte is 1,024 kilobytes and so on
and so in total, a 500 gigabyte drive will be read
by say Windows 7 as 465 gigabytes, so that's capacity.
Next is cache.
Cache is a buffer of memory
and the cache on most hard drives is on-board DRAM,
it's right on the circuit board to the drive.
And you can compare this with CPUs,
CPUs have cache memory which we've spoken of,
and they use SRAM and that's significantly faster than DRAM,
but, like the CPUs, the hard drives cache
helps to access frequently used information
faster than if it were to get it from the magnetic disc,
in fact, a lot faster, you know, your on-board
DRAM's gonna be much faster than the magnetic disk.
So there's capacity and cache,
let's look at our hard drive again and show those
on the label of the drive and show what they mean.
Okay, here we're looking at the top of the drive
and we're looking at the label,
we see this as a Western Digital 500 gigabyte
Caviar Blue drive, just the basic drive
for holding basic data.
But we also see here that it says SATA
so we know the type of drive, and it says 16 megabytes
of cache, so we know how much cache memory this drive has.
Newer drives today have a lot more cache and faster cache.
We also see here the model number, WD5000AAKS.
Now it's important to know the cache
and the model number, and perhaps even
the serial number here, whenever you are replacing a drive
because you should replace the drive
with the same drive usually unless you're upgrading,
but also if you're gonna create an array of drives
say a RAID 1 or a RAID 5 array, or any type of array.
You wanna use the same type of drive
for all the drives in the array
and you really wanna go by this model number
when you do that.
So make sure that all the drives are WD5000AAKS,
because the model names can be slightly different,
like AAVS or WD5000ABKS, or what have you.
So you wanna be real careful with that and check that
make sure that you're using the correct drive,
using the same drives for all of them within the array.
We also have a schematic of the connections
showing you where to connect the power and the data
and so on and if you have to make any changes
to the jumper settings,
it gives you that information there.
So always look at the label, the drive it can give you a lot
of information that you need to know as far as connecting it
or compatibility or exactly what type of drive it is
if you can't find this information within your bios
or within your analysis software.
Okay, getting back to hard disk specifications,
let's talk about data transfer rate.
The data transfer rate of a hard drive
is the maximum amount of bytes that can be sent or received.
But it's a theoretical maximum and the theoretical numbers
are never really actually achieved,
generally, you'll get a data throughput amount
that you actually are using,
but, you should know the data transfer rate maximums
for SATA and you can see those are listed here.
First, we have SATA Revision 1.0
and we see that it's measured in bits and bytes,
so 1.5 gigabits per second will basically
come down to being 150 megabytes
of data being written to the drive per second.
Now you may say, well, why didn't we just divide by eight?
And the reason that it's only a 10th of the data
sent serially is because of encoding.
You have some additional encoding data
that has to be removed after it gets to the drive
before that data can be written to the drive.
So you lose a little bit there,
so 1.5 gigabit serial connections
will actually store 150 megabytes of data per second
on the drive.
Then we have SATA Revision 2
and you'll see a lot of these drives out there,
there are three gigabytes per second
and they can write a maximum of 300 megabytes per second
to the drive.
Now, our drive is an SATA Revision 2.0 drive,
so it has this theoretical maximum of 300 megabytes
per second, but this particular drive
can only sustain in the neighborhood of say 120,
130 megabytes per second
and this is also referred to as data throughput,
the actual amount of data that you can send back
and forth in your computer, in your environment.
So, in my environment, in my lab, that's about what I get
on this magnetic disk, 120 megabytes per second,
the theoretical maximum is 300 megabytes per second.
So, some food for thought there.
Next, we have SATA Revision 3
and we have one of those drives going into our AV editor
also and that's six gigabytes per second
or 600 megabytes per second.
And now we have SATA Revision 3.2
as of the recording of this video, that's the latest one
and that goes at 16 gigabytes per second
and has less encoding data,
so we actually get a better ratio
and it's upwards of 1,969 megabytes per second
or two gigabytes of data per second,
so that's a big jump, and that is data transfer rate.
Couple other things you should know
for hard disk specifications;
the first is rotational speed.
This only deals with magnetic hard drives
and some examples are 5400, 7200, or 10,000 RPMs
or rotations per minute.
The rotational speed is something that you might look at
when you're interested in how fast the data can be accessed.
If you need really fast data access, you wanna higher speed.
If you don't really care that much,
if you just have a computer that's connecting
to the internet, you might wanna just go with 5,400 RPM.
Why?
'Cause there's a cost factor involved,
the drives with the higher RPMs are gonna cost more money.
But again, the drives with the higher RPMs
have faster access times
because there's less seek time to get the information
from the particular sector and track on the drive.
Now this is tied into another term called latency.
After a track has been reached by the read/write head,
latency is the delay in time before a particular sector
on that platter can be read.
So that's how long it takes for the platter to spin around
for the read/write head to actually get that data,
and it's directly related to that rotational speed.
It's usually half the time it takes
for the disk to rotate once.
So for a very common 7,200 RPM drive,
the average latency will be 4.2 milliseconds,
but, for a faster drive that runs a 10,000 RPMs,
it'll be a lower latency, say around three milliseconds.
So those are some of the hard dis specifications
you should know, capacity, cache, data transfer rate,
rotational speed, and latency.
And if you get a chance, get yourself a magnetic hard disk
and take a look at it, look at all the ports,
look at the information on the label
and see how it works, connect it into your computer,
see how the actual drive functions.
So that's about it for this sub lesson.