[ Silence ]
>> R.J. Aquino: Hi everyone.
Thanks for staying long or watching the video online.
If you watched the video online, I'm R.J. You may know me
from such videos as Taking Apart your Computer,
Crimping Your Ethernet Cable, among other great shorts.
But for this review session, the plan really is to sort of,
we have a lot of material prepared,
we want to just help you, sort of,
whatever you want to go over.
So we've sort of put up on the screen the recap summary list,
and if we can make a list of topics we're going to go over,
and then we'll just sort of go through them.
So, any sort of general topics in particular
that you remember being confusing or you sort
of don't quite have a full handle on?
Anything at all?
Starting over here.
>> Just one question.
Are we allowed to ask in terms of...I'm curious
about the format of the exam [inaudible]
>> R.J. Aquino: Oh, yeah, we have a slide or two about that.
So we'll definitely talk about that.
>> [Inaudible]
>> R.J. Aquino: Yep.
And the question was about the format of the exam,
so we will go over that.
Yeah, and if there aren't, sort of, broad general questions,
we can, sort of, pick a topic and jump in, but...yeah?
>> There's one on the, what is it?
HDD drives and then the SSD drives, the difference
between how like you access the information.
Like, I know that one is faster than the other,
but I didn't understand the process
in which your computer will fetch information on an SSD...
>> R.J. Aquino: Yep, so HDDs and SSDs.
We'll definitely go over those.
I'll just make a list, so we remember.
>> Ben Shryock: Anything else from other members of the class?
>> R.J. Aquino: Yep?
>> Um, well, I just need to remember SATA
and PATA, both of those.
>> R.J. Aquino: Okay.
Great.
>> And binary too.
>> Ben Shryock: Binary.
>> R.J. Aquino: Yep.
That's a good one.
>> Ben Shryock: In terms of binary, how do we feel about,
like, converting decimal to binary, converting binary
to decimal, or binary addition?
Sort of all of those things, or is one...
>> All of them.
For me, all of them.
>> Ben Shryock: Great.
>> R.J. Aquino: We have a prepared example for that.
Um, anything else?
And we can always sort of...yeah?
>> I was going to suggest the binary operators,
but I don't know if we want to go through that...
>> R.J. Aquino: Yeah, so the bitwise operators...
>> Bit...
>> R.J. Aquino: Yep, so those actually are technically not
going to be on the exam because there is a [inaudible]
of the video only.
But definitely, if you have any questions,
feel free to ask them.
But, yeah, so we can do the [inaudible],
the first few slides if you hit the three.
Three. Four?
Three or four.
>> Ben Shryock: Let's try three.
>> R.J. Aquino: Let's try three.
>> Ben Shryock: Let's try four.
>> R.J. Aquino: Let's try four.
Okay. So...
>> Ben Shryock: Go ahead.
>> R.J. Aquino: So, yeah, here is some administrivia.
Administrivia is a big word for...I don't know what
it means.
The exam is going to be next Monday, right here,
five-thirty to seven-thirty.
It will be two hours.
You will have two hours to complete the exam.
The [inaudible] all sorts of policies.
Tommy mentioned this in lecture.
But things about...if you're taking a distance,
you should follow those normal rules.
The exam will consist of questions.
The questions will be sort of, probably things like fill
in the blank, short answers, multiple choice, really similar
in spirit to the problem set questions
and lectures one through four.
So the first four weeks
of the course will be represented relatively equally,
so about a quarter from lecture one, two and three
and four, not and so on.
One, two, three, four.
No calculators, notes, or other aids.
And the section videos, while useful in helping you sort
of synthesize the information and remind yourself of things
from the lectures,
won't specifically be tested on the exam.
In terms of like studying, I know Tommy mentioned a lot
of this in his lecture component, but, you know,
the recaps are really helpful.
The recaps are what, you know, frankly we use
to prepare these review slides.
And they are a really good sort of way to review the material.
I would recommend not just sort of reading through them
and saying, oh, I understand that, I understand that,
but definitely take time to pause yourself, take a break,
and see if you remember what you read five minutes earlier
because it's pretty easy when you're reading it to say, oh,
that sentence makes sense, I understand it.
And then when you come to the exam,
realize you don't remember the things that you read.
So in terms of studying, I'd sort of read through a recap
and then try the practice problems at the end
or maybe read the recap, leave for half an hour,
maybe watch an episode of TV or, you know, eat a meal,
something like that, and then go back to the practice questions
after a break to see if you really remember the material.
Tommy's got a question.
>> Tommy: Since the recaps also have practice questions
that are not on the problem sets, so just kind
of some additional questions
that you might want to practice with.
And also, keep in mind, the recaps do have some information
that was not covered in lecture, just for time constraints
or because it was less interesting.
So if there's something in a recap that we did not mention
in lecture, then you know that's not going to be on the exam
because that's not fair.
If we covered it in lecture,
then that will be covered on the exam.
>> R.J. Aquino: Yeah, so what Tommy said was
that there are practice questions at the end
of the recaps that have questions that were not
on the problem sets, and those are very useful for practice
and that the recaps potentially have some more detail
than what was covered in lecture,
and that detail is useful for extra knowledge
and for really going over things that we didn't have time
for in lecture but aren't necessarily game for the exam.
So if it was in lecture, it can be on the exam.
If it was in a recap, but it wasn't in lecture,
then you don't need to know it.
It's just sort of fun.
Okay. And I would recommend going over your problems sets.
So the problem sets you submit have feedback online,
and marking the questions you got right, which are great,
and also the questions you got wrong.
And so definitely look at your feedback and sort of go
over the ones you got right and make sure you still know how
to do them and then especially go over the ones you got wrong
to see, you know, what you did wrong and what, you know,
the right answer was, so you can get it, you know, right,
hopefully, on the exam.
But let's sort of just talk about topics now.
So, one question was about HDDs versus SSDs.
So I have a slide.
We've got...here we go.
So an HDD, in particular, has a lot of mechanical components.
And I know the question specifically asked about SSDs,
but we might as well go over HDDs as well.
So we have the magnetic platters, and the whole sort
of process is in a recap, but the platters are divided
into tracks and sectors, and so the magnetic head
of the read-write...I'll leave one for the video.
The magnetic head of the actuator arms reads
over the platters to read the magnetic bits off the drive,
and that's a very mechanical process,
whereas the SSDs have no moving parts and are sort
of flash memory, a lot like RAM.
So they're no moving parts involved, and the data is sort
of read off of those, like, much like you read off RAM.
That sort of...
>> Ben Shryock: I think to return your question,
if you're getting at what's covered in the recap,
which is a little more about NAND gates and transistors,
if we didn't cover it in lecture,
as Tommy was just saying,
then we will not cover in on the exam.
>> R.J. Aquino: And, correct me if I'm wrong,
but I don't think we talked about that level of detail.
Yeah, that level of detail for SSDs, while useful and fun,
isn't necessarily needed for the exam.
>> Ben Shryock: Yes.
Does that help?
>> R.J. Aquino: So what was the next thing on our list, which,
I'm realizing a short list?
SATA versus PATA, so if you could hit three,
[inaudible] slide.
Do you have the recap part here?
>> Ben Shryock: Sure.
Oh, this is a memory thing?
>> R.J. Aquino: Just...
[inaudible]
>> Ben Shryock: Because I was looking here.
>> R.J. Aquino: Yeah.
Let's use this one.
Do you have a slide for this?
>> Ben Shryock: This is fine.
>> R.J. Aquino: Okay.
>> Ben Shryock: So would you like to explain?
They're both...SATA and PATA.
PATA also can be referred to as an IDE connector or ways
of connecting the hard drive to the motherboard.
Tommy, are there specific differences
that we're expecting students to know?
>> Tommy: Probably, you know, there are different types
of cables, you know, SATA is kind of a newer version.
It's faster.
The cables could be longer, actually.
But just, you know, there are two different ways
of connecting the hard drive to the motherboard.
Most, pretty much all modern hard drives are SATA.
If you ever see that kind of ribbon cable, that's what it is.
>> R.J. Aquino: Yeah, so just to say it again for the camera,
the SATA and PATA are just both ways
of connecting your hard drive to your, sort of, motherboard,
but SATA is a newer type of connector,
and most hard drives these days are SATA.
But if you ever see some of those older, big ribbon cables,
that's a PATA connector potentially.
So, you know, the motherboard we looked at had both,
but these are...if you look at a computer these days,
there will be a [inaudible] and a SATA connector
and then plug into your hard drive.
>> Ben Shryock: Does that answer the question?
Feel free to ask followup questions as we talk,
or once we finish covering these three things,
we can answer some more.
Something else?
>> I was just wondering if we needed to know
like what SATA stands for because we use a lot of...
>> R.J. Aquino: Acronyms.
>> Acronyms, and what's important to know.
>> Ben Shryock: So the question was, if students are expected
to know things like SATA and what that acronym stands for.
And I think, in general, if we defined it in class,
then it would be good to know what it stands for.
But things like SATA or PATA,
which I don't believe we defined, then it's not
as important that you know the acronym.
It's just important that you know what they do.
>> Tommy: It's more important
that you know what the acronym is
than what the letters actually stand for.
So knowing, you know, that SSD has to do with,
it's a type of hard drive versus SMTP, which is a, you know,
we just looked at some email.
So just like knowing what they are, but, you know,
you don't have to reproduce like what the DHCP stands for.
>> R.J. Aquino: Yeah, and I was going to say the same thing,
and I'll say it again because camera.
It really is important.
If you know the letters,
you will likely then know what it means
and what the thing does.
But if you don't know the specific letters,
as long as you know that, oh, SMTP is a mail protocol.
You know, it's helpful that you remember that M and P are mail
and protocol, but if you don't remember whether it's secure
mail transfer protocol or simple mail transfer protocol
or super mail transfer protocol isn't super important.
But definitely, if it's easiest for you
to just memorize all the acronyms
and that's how you'll remember what each one does,
then great, do that.
But if it's easier for you just to remember, oh,
SATA and PATA are two types of connectors
and SMTP is an email thing, then that's really the level
that we want you to understand what these things do.
It's much better if you can describe, sort of,
in a couple sentences what SMTP is used for rather
than just telling us what the letters stand for.
And those will be the types of questions, you know.
I would highly doubt that we would put like a list
of acronyms and a list of things, have you match them,
because if you know anything right now,
that would be really easy
because it would have the letters.
But we would say, you know, SMTP,
describe what it's for, you know.
DHCP, potentially describe what it's for, but not just,
hey, give us the acronym.
That's not a useful use of our grading time really.
>> Ben Shryock: Or your brain power.
So shall we move on to binary?
>> R.J. Aquino: Yeah, so give an example...
>> Around thirty, slide thirty.
>> R.J. Aquino: Oh, well...
>> Ben Shryock: It's near the beginning.
>> R.J. Aquino: Yeah.
>> Ben Shryock: So I think we'll start with just some conversion,
like converting binary to decimal and decimal to binary.
>> R.J. Aquino: Pull up one of those.
>> Ben Shryock: Oh, nailed it.
All right.
To start with...
>> R.J. Aquino: ...with the screen to move the slide.
>> Ben Shryock: I do what to who?
Yeah, thank you.
Okay. So if we have a number like this, 10101,
does anyone remember what the general process we might use
to convert this to decimal is?
Going back to binary.
That's kind of a long time ago.
Yeah?
>> [Inaudible]
>> Ben Shryock: Oh, yeah.
Right here.
No?
>> Was it two to the zero power, two to the one power,
two to the second power?
>> Ben Shryock: Exactly.
So the first bit, this one
on the very right-hand side is like the one's place.
It's two to the zero.
And the next one is like a two's place and then a four's place
and then an eight's place.
Each one increasing by two.
So if we sort of write on the board, maybe if we were actually
to do this problem on an exam, we could just take this
and make our like...can people see the chalkboard
if I write over here?
Write like our five dashes, and this is the one's place,
this is the two's place, this is the four's place,
eight, and sixteen.
>> R.J. Aquino: And if I can jump in for a second.
It's very, very common, especially in a test situation,
that you'll make a little mistake
and say the zero's place instead of the one's place.
So definitely...and that happened a lot, you know,
on the problem sets, so definitely keep track and go,
one, two, four, eight, sixteen, not zero,
two, four, eight, sixteen.
>> Ben Shryock: Yes.
Great reminder.
So then if we look at our number, we have five numbers.
So the first one goes here in the one's place.
We have a zero in the two's place.
One here, zero here, and one here.
Any questions about how we got to this point?
And so then just like we were adding up numbers
in the decimal system, we can say, oh, a one in a one's place,
that has a value of one.
Zero in the two's place, that has a value of zero.
We're just going to sum these up.
One in the four's place is a four.
Zero in the eight's place is zero.
And a one in the sixteenth place is sixteen.
So when we add those up, it looks like we get twenty-one.
And if we look at the slide,
it's the same process outlined that I did here.
Do you have any questions about this?
Yeah?
>> So it goes right to left instead of left to right?
>> Ben Shryock: You could think of it as either way.
I think it's easiest to start from the right because you know
that this is always going to be the one's place,
whereas if you have like maybe a,
if we give you a longer binary number, the farthest
to the left might not be the sixteenth place.
It might be the thirty-second or the sixty-fourth.
Yeah?
>> This might be stupid, but instead of writing one, two,
four, eight, sixteen, can you write two to the zero,
two to the one, two...
>> Ben Shryock: Yes, and that's almost even better
because that's where these numbers are coming from.
So the question was, instead of writing one, two,
four for the places, could you write two to the zero,
two to the one, two to the two, two to the three,
and the answer is, yes, that's completely correct.
>> R.J. Aquino: And I will just say it one more time.
I see that all the time, and the people that wrote two
to the zero, very, very, very often, accidentally said, oh,
two to the zero is zero.
So as long...it's actually...it definitely is sort of easier
and faster to write two to the zero, two to the one,
two to the two, but just make sure you keep track of, well,
two to the zero is actually one, and so you're not,
you don't put twenty instead of twenty-one.
But, yeah, no, it's...and that's particularly useful if you want
to do something other than binary.
Like if we said, oh, it's base three or it's base seven,
then it's three to the zero, three to the one,
three to the two, or...am I even on camera?
Am I just standing off screen on voice?
Or seven to the zero, seven to the one, seven to the two.
>> Ben Shryock: I want to do this again if you are.
>> R.J. Aquino: So that definitely makes it clear
that you know exactly what's going on with the base system.
>> Ben Shryock: Anymore questions on this example?
So this was a pretty simple example, but it's [inaudible]
that you can follow anytime you need
to convert some binary number to a decimal number.
So, if it would be helpful, we'll now go onto a decimal
to binary conversion example.
R.J., do you want to take this one away?
>> R.J. Aquino: It's your slide.
I do it wrong, I'm sure.
>> Ben Shryock: All right.
I'm quite confident that R.J. can convert twelve
to a binary number, but he's going to let me do it.
So does anyone remember the process we might use
when we're going from decimal to binary?
Yeah?
>> [Inaudible] how many times does twelve go into two
to the four or two to the three...
>> Ben Shryock: Perfect.
Yeah. So what I have here is
like the five blanks, bases, on the slide.
Do you want to do the writing?
>> R.J. Aquino: Sure.
>> Ben Shryock: Nice.
All right.
And so we can think of it as pretty much the same way.
We have our five spaces, each corresponding
to like the one's place, two's place, four's place.
And what we can do is just start on the left this time and say,
how many times does twelve go into sixteen?
Let's hear from one of you.
>> Zero.
>> Ben Shryock: Zero times.
So twelve into sixteen.
>> R.J. Aquino: So...
>> Ben Shryock: Did I misspeak?
>> R.J. Aquino: Yeah.
Sixteen into twelve.
>> Ben Shryock: I did misspeak.
You're correct.
But they just knew what I was trying
to say even though I was wrong.
So sixteen into twelve zero times.
But then eight, how many times can that fit
into whichever way it goes?
One. So we can just progressively move further
down this binary number.
And so now...
>> R.J. Aquino: So if I put an eight...
>> Ben Shryock: Yes.
It's important to sort of subtract that total
from our previous total.
Does everyone understand why we would do that?
>> R.J. Aquino: Now, we put in this eight.
We've accounted for the eight, but there's still four left
over that we're going to want to include, and so you just have
to make sure that you start big enough that, you know,
you've accounted for everything.
So we kept going until we found a number bigger than twelve.
So one isn't bigger, two isn't bigger, four, eight.
Sixteen is bigger, so we know that's as far as we need to go.
Zero sixteens and then one eight and now...
we started with twelve.
We've accounted for eight of those twelve,
and there's still four left over.
And now keep going.
>> Ben Shryock: Great.
Perfect way to explain it.
So now that we move back to the four's place, do we need a four?
Yes. And so once we include that four,
have we represented all of the number?
Yes. So then we can just kind of see, there's nothing left,
so the rest of our places are going to be filled with zeros.
>> R.J. Aquino: And so one other little detail of binary.
You know, here we have written up zero, one, one, zero, zero.
I could have said, zero, zero, zero,
zero, one, one, zero, zero.
The zeros to the far left just don't matter.
>> Ben Shryock: Yes.
>> R.J. Aquino: The zeros on the right are important.
The zeros on the right say that this first one is going
to be a four as opposed to an eight or a one or a two.
So you need these two zeros to make sure that you're sort
of lined up correctly, but then the other zeros don't matter.
>> Ben Shryock: Question.
>> So does that mean that you can just call it one,
one, zero, zero?
>> R.J. Aquino: Yes.
>> Ben Shryock: Yes.
>> Okay.
>> R.J. Aquino: We're talking about, sort of, computers
and how they represent information, things are,
you know, sort of just bytes, which are eight bits long.
So typically you'll see these numbers, sort of,
padded out to eight numbers.
And in some cases, you know, a number might be two bytes,
so we say, okay, every number is going to be two bytes.
So you're going to have, you know, maybe fourteen extra zeros
or twelve extra zeros or something But, yeah,
this number...if I said, in binary one, one, zero, zero,
that's twelve, and so on.
>> Ben Shryock: Yep.
And so if we see the slide, kind of the same process.
Would it be helpful to do...well, first,
do we have anymore questions on that conversion?
>> R.J. Aquino: So any other topics now
that we've sort of warmed up a bit?
>> Ben Shryock: Yeah?
>> I was kind of wondering about CNAME and ANAME or [inaudible]
>> R.J. Aquino: Are those your internet slides or...
>> Ben Shryock: No.
Oh, yes. They are.
>> R.J. Aquino: Okay.
>> Ben Shryock: So what level it's controlled.
>> [Inaudible] I think I'm a little confused with the CNAME.
>> Ben Shryock: Sure.
>> In terms of which one to use first
or which one is more [inaudible]
>> Are they subdomains or...
>> R.J. Aquino: Let's find this slide.
Here we go.
[Background discussion]
>> Ben Shryock: Are you good?
>> R.J. Aquino: Your slide, unfortunately.
So if we, actually, can quote from one
of the recaps here, I think.
You happened to pick a slide that Ben prepared,
so Ben is going to talk for a bit.
>> Ben Shryock: Okay.
So you're just sort of asking about the DNS records and sort
of these different fields that we see in those things?
Is that correct?
>> Yeah.
>> Ben Shryock: And CNAME and ANAME is part of that?
Okay. So I think this is the exact slide, actually,
that Tommy showed in lecture.
So we see that...were you wondering specifically
about the CNAME and the...
>> Well, when you say like a domain alias,
I don't really get it, like, is it another domain
that redirects from the original?
>> Ben Shryock: Exactly, yes.
So the question was, when we say that it's a domain alias,
does that mean that it's a separate domain
that aliases to the same domain?
And, yes, that's exactly the correct way
of thinking about it.
>> R.J. Aquino: So if you had a CNAME for, let's say,
is there an example you could give?
>> Ben Shryock: Let me...yes.
In the recap, there's a display, which I just pulled up of,
which, I believe, we looked at in lecture,
which is like a DNS record
that you might actually see on your internets.
So here at the very bottom, we see these CNAME records,
and we have some hostname mail, which aliases
to this GHS.google.com address.
>> R.J. Aquino: So is that mail.cse1.net, Tommy?
>> Ben Shryock: Yes.
>> R.J. Aquino: So if we go to mail.cse1.net,
it sort of aliases to Google's mail servers,
and we actually end up at, sort of, a Gmail, like, interface.
So in this case, even though Tommy owns cse1.net,
and he has connected it to one of his, sort of,
servers that's serving all this content, like the recaps
and the lectures and things, when he goes to mail.cse1.net,
the requests are actually sent to Google
and you get a Gmail like...because Google is
preparing that Gmail page, not Tommy.
>> Is that reflexive at all?
I mean, is there any way, would Google also [inaudible] cse1?
>> R.J. Aquino: I know for, in this particular example,
Google let's you do, or mail.google.com/a/cse1.net,
I don't know if that's always the case.
>> Okay.
>> R.J. Aquino: Is there always a way to...
>> [Inaudible]
>> R.J. Aquino: So it's not necessarily the case
that if you have a CNAME to a particular web server,
you can actually get there another way.
You may only be able to get there through the CNAME.
>> Ben Shryock: Question over here first, and then we'll...
>> [Inaudible]
>> Ben Shryock: Do you know this?
>> R.J. Aquino: I think I do.
>> Ben Shryock: Go ahead.
>> R.J. Aquino: So my understanding,
and I'm sure someone will jump in if I'm wrong,
is that when you go to mail.cse1.net,
you're sending a request through cse1.net, which is sort
of configured to today...well hold on.
The mail host, that's actually this Google address,
so go there instead.
>> [Inaudible]
>> Ben Shryock: Let me pull up.
>> R.J. Aquino: Do you have it?
>> Ben Shryock: Yep.
Sure. So I think this...
>> R.J. Aquino: That's not it.
Wrong one.
>> Ben Shryock: Delightful.
Take your time.
So I think this slide is kind of getting at more of your point,
which is a little different than CNAME, but related.
So this is talking about, sort of, the order that we go
in when we're trying to make a request, correct?
So, first, you would go to the cache DNS server if it's not in,
sort of, your personal host, right?
And then if you search a few nearby DNS servers
and don't find anything, that's when you move
onto the root DNS server.
>> R.J. Aquino: When you say you,
you don't mean actually one of us, but...
>> Ben Shryock: But a client making a request.
>> R.J. Aquino: Yes.
So some process that you sort of kicked off that you're no longer
in charge of goes off and does all this?
>> Ben Shryock: Correct.
>> [Inaudible]
>> Ben Shryock: Exactly, yeah.
So it's going...
>> R.J. Aquino: Repeat.
You can't say exactly.
>> Ben Shryock: Oh.
>> R.J. Aquino: Exactly what?
>> Ben Shryock: Yes.
No, I understand.
So she asked, if you go to sort of a different server
or a different router, and that's exactly what happens.
First, it checks the cache DNS server,
then it checks other nearby.
Nearby, in terms of things that that server maps to,
and then if after a few of those don't yield the IP address
that you're looking for, then you move
onto this root DNS server.
Does that help answer your question?
>> Yes.
>> Ben Shryock: Great.
And you had a question over here?
>> Going back to the CNAME.
>> Ben Shryock: Yeah.
>> What does the alias mean [inaudible]
>> Ben Shryock: Oh, sure.
So alias is just...to say two things are alias means they do
the same thing.
So typing in mail...do you want to switch?
>> R.J. Aquino: Yeah.
>> Ben Shryock: Switch back.
>> R.J. Aquino: Oh, what did I just hit?
>> Ben Shryock: All right.
Technical difficulties.
>> R.J. Aquino: Found it.
>> Ben Shryock: Typing
in mail.cse1.net does the same thing as this ghs.google.com.
>> R.J. Aquino: Yeah.
>> Ben Shryock: So that's essentially two names
for the same thing.
>> R.J. Aquino: Yeah, the word alias just means a name
for the same thing.
>> Ben Shryock: Yes.
>> R.J. Aquino: So, in this case,
an alias is to...or mail.cse1.net is an alias
for this ghs.google.com.
So it's just a name for ghs.google.com.
>> Ben Shryock: Question.
>> Is there or is there not an IP associated with the CNAME?
>> Ben Shryock: So the question is, is there
or is there not an IP address associated with the CNAME?
>> R.J. Aquino: So my understanding is
that there will eventually be an IP address because there has
to be to send a request and receive a request,
but we are not in charge of it anymore.
We've sort of handed off control to Google and said, hey,
in this case, you know, ghs.google.com is going to sort
of have its own entry and its own, you know, its own server,
and it's going to have its own IP address.
So, as far as we're concerned, if you're looking
for mail.cse1.net, you know, we're just going to hand it off
to the next, sort of, guy.
Yeah?
>> [Inaudible] A records,
you would be handling all [inaudible]
>> R.J. Aquino: Right.
So if we scroll up here to these A records, you know,
our DNS [inaudible] in this case, sort of,
we're in charge of that.
It's our site and...
>> Ben Shryock: So we are completely in charge
of the IP address whether that's an A record,
which would be an IPv4 or a quadruple A,
which would be the IPv6.
More questions on this topic or other topics?
We can put up the list of recaps again.
>> R.J. Aquino: Really, anything at all.
>> Ben Shryock: Yeah?
>> Just back to the binary real quick.
Are we going to have the octal system on the exam?
>> Ben Shryock: Quite possibly since it's been covered on...oh,
the question was...I apologize.
The question was whether the octal system could be covered
on the exam.
And since it was covered on a problem set,
I think it's completely fair.
And I think it would also be fair of us, just like we kind
of threw the octal system at you, to maybe give you something
that was not binary nor octal nor decimal and hope
that you kind of figure it out, more general process each
for how you might work in different bases.
>> R.J. Aquino: That being said,
don't be worried about massive...
>> Ben Shryock: Yes.
>> R.J. Aquino: ...large mass.
Obviously, no calculators on the exam, so numbers...
>> Ben Shryock: Yes.
>> R.J. Aquino: ...will be small and workable as long as,
you know, in sort of this realm as opposed
to the multiply a thousand and fifty by six hundred and twelve.
>> Ben Shryock: Now, I realize we never did a binary
addition problem.
Is that something people would find helpful?
Do you remember how to add binary numbers together?
Let's raise hands if we would like to see a binary addition.
All right.
Let's do binary addition.
>> R.J. Aquino: Okay.
Do you have a slide?
>> Ben Shryock: I do not have a slide for this.
>> R.J. Aquino: Okay.
>> Ben Shryock: But we have a chalkboard.
>> R.J. Aquino: Great.
>> Ben Shryock: Do you want to talk and I'll write?
Do you want me to write?
>> R.J. Aquino: Sure, I'll talk.
Do a binary...okay.
I'll talk.
>> Ben Shryock: What are your favorite numbers?
>> R.J. Aquino: In binary?
>> Ben Shryock: Yeah, in binary.
>> R.J. Aquino: One zero one one and zero one one zero.
Would that turn out good?
>> Ben Shryock: I have no idea.
>> R.J. Aquino: It will turn out fine.
>> Ben Shryock: Yeah.
>> R.J. Aquino: Okay.
So if we asked you to, say, add one zero one one
and zero one one zero, one thing you could do is just take both
of those numbers, convert them to decimal, add them,
and then convert it back to binary, which would work
and you'd probably get the right answer,
but it would take you presumably a lot longer
because if you do two conversions to decimal,
one conversion back to binary,
and it will just take a long time.
So we can actually do the entire addition
if you put a plus sign for addition.
We can actually do the entire addition in the binary here.
And is this something we covered in lecture, I'm thinking about?
>> Ben Shryock: Hm mm.
>> R.J. Aquino: Okay.
Then let's definitely go along and keep doing this.
So like, sort of, our standard decimal addition,
we'll start on the far right, and we'll add one and zero.
And what's one plus zero?
>> One.
>> Ben Shryock: All right.
>> R.J. Aquino: And that's probably a level
of math...it's one.
That's the level of math we're talking about in this.
>> Ben Shryock: You'll have to go up to two, actually,
and then maybe bring it back down to zero.
That's what we're about to see.
>> R.J. Aquino: So, here,
on this next one, we have one plus one.
And one plus one is two, which is great and awesome, but,
unfortunately, not one of our options in binary.
We only have one and zero to play with.
So like when you get above ten when adding, if you were adding,
if we had six and five there, you'd get eleven,
and there's no way to write eleven.
So you have to sort of carry.
In this case, one plus one is two,
which is one zero in binary.
So if Ben could put a zero below and a one to the top left,
we sort of carried the one, as it were.
Does that step make sense?
That's really the only tricky thing with binary addition.
Other than that, it's like regular addition.
So are we following where that carry came from?
Yeah? Great.
Great. We keep going, and we get one plus one plus...well,
one plus zero plus one, which is, again, two.
>> Ben Shryock: So we'll make this zero.
>> R.J. Aquino: So we have
to do the whole one zero carry thing again.
>> Ben Shryock: Carry the one.
>> R.J. Aquino: And we're going to do it one more time,
but this time, again, one plus one plus zero.
This time, we can't quite carry anywhere,
so we'll just tack the one on the end.
Kind of like if you were adding...you know,
if you do a decimal example,
you'll see that it's actually exactly the same way.
And so we get one, zero, zero, zero...we get one,
zero, zero, zero, one.
And just to confirm,
let's actually do the long process, I mentioned earlier.
This is one plus two plus eight is eleven.
And this is two plus four is six.
And this is one plus sixteen is seventeen.
And eleven plus six is, indeed, seventeen.
>> Ben Shryock: So you can see that either way works,
although if we set up something on the test that was
in this format, we would kind of like you
to do the actual binary addition and show your work
with the carries as opposed
to just convert them both to decimal.
>> R.J. Aquino: Yeah, and I happened to do that one
in my head because I got lucky.
Normally, when I do math in my head,
it goes horribly, horribly wrong.
So I would definitely recommend doing it, sort of, the right way
with the carries and writing all your work
down so you're less likely to make a mistake.
Plus, in the off chance you do make a mistake, if we see work
that is sort of on the way to the right answer,
we can give you partial credit, whereas if you just write
down a wrong answer with no indication
of what you were doing, there's really no credit we can give you
for work that wasn't shown.
So when in doubt sort of show your steps.
>> Ben Shryock: Any questions on this process?
>> R.J. Aquino: Yeah, so binary addition, actually,
it's weird the first few times you do it.
It's uncomfortable because you're carrying, you know,
lots of ones and zeros floating around,
but it's actually very similar to decimal addition.
>> Ben Shryock: Should we do some binary subtraction,
multiplication, long division?
I'm just kidding.
>> R.J. Aquino: Please.
Long division, I...
>> Ben Shryock: So other topics from the recaps
that are on this list?
>> R.J. Aquino: Yeah?
Was there a hand, or...no?
So, I mean, things that we could, sort of, toss at you.
If we threw up one of these pictures
with just the yellow lines and no...oh.
>> Do you know if today's lecture...
>> Ben Shryock: Today's lecture is completely fair game.
>> R.J. Aquino: Fair game.
We were here.
We were listening.
>> The whole, like, manual email
and like can you go over that [inaudible]
>> R.J. Aquino: Yeah.
>> [Inaudible]
>> R.J. Aquino: So I imagine
that the technical details probably aren't super important,
but...oh, the question.
So the question was about today's lecture.
We went over a bunch of protocols
and whether we could talk about, sort of, the manual sending
of email, for example because we showed an SMTP example.
So...oops.
Oh, but my slide wasn't very helpful because it's telling us
to go to the recap, which we will do.
So we'll pull it up in a second.
But just to go over SMTP,
it's the simple mail transfer protocol, and when we go onto,
sort of, Gmail.com and we say, we type in a message
and hit send, it, on our behalf, does a number of steps.
It connects to an SMTP server of the recipient,
and it prepares the header, saying who the message is from
and where the message is going, and it prepares the message
and prepares a bunch of other information that we'll see,
and it sort of sends that request.
It forms a connection, sets something up, you know,
sends data, types in all the things it needs to say,
and sends it on its way.
So we can actually manually do that process,
but Gmail does it for us.
So if we pull up the recap, which I had it all typed up,
but I didn't want to squeeze it onto a slide.
>> Ben Shryock: Oh, I was...
>> R.J. Aquino: You were [inaudible]
>> Ben Shryock: I sure was.
>> R.J. Aquino: So this, you know,
an example of what is actually sent, and it's...here, hold.
We can zoom.
This is the headers
of an email...not what we're looking for.
So here...what?
Oh. It's not it either?
Well, that's the connection...yep.
Log in. Log in.
[Background voices] I'm looking at it.
>> Ben Shryock: Look.
There it is.
>> R.J. Aquino: Oh, it's the whole record.
Oh, because Tommy was nice.
He walked us through it step by step,
but here's the entire thing.
So we formed a connection.
We logged in with our username and password in Base64,
which is magic for letters and numbers
and a couple of other characters.
It's the uppercase letters, lowercase letters,
some punctuation involved there.
But once you've logged in, we say, mail from,
and we type in who it's from.
We say, rcpt to, and, again, the details of the command is mail
and the rcpt aren't probably super important to, you know,
memorize but definitely recognize what they're
doing here.
We type in data, which is just a sign to the SMTP server
that my message is about to start.
It tells us to go ahead, and it pre-populates this from
and to, or we type that?
>> Ben Shryock: You type it.
>> R.J. Aquino: Okay.
So we typed in...after data, we typed in from,
and who it's from, and to, and who it's to.
>> Ben Shryock: Just like how we want to pretend
to be barackobama@whitehouse.gov,
we can do that here.
>> R.J. Aquino: And we type in a subject, like, I love cats,
and then the body of our message.
So here it's just a sentence.
It could have been paragraphs and paragraphs and paragraphs,
could have been up to some limit,
could have had [inaudible] involved.
And then when we're done, we hit a dot, hit enter.
And at that point, the SMTP server kind
of sends it on its way.
Yeah?
>> So which part [inaudible]
>> R.J. Aquino: So it's important
to understand the steps that are going on.
I mean, I would, sort of, in this case,
there are only a few commands, so mail, rcpt,
data might be useful to sort of memorize,
although I don't know the test, so it's hard to say for sure.
But the understanding that there are these sorts of steps going
on under the scenes or under the hood, behind the scenes,
when you sort of hit send in Gmail.
>> So basically, like, look for understanding
like that there is this kind of two-way communication going on.
Like, first you would say, who's the email from,
then you would say, receipt to, [inaudible] the actual like,
the letters you must type for it to develop.
It's kind of like on a conceptual level.
You're having a conversation with the server,
you're seeing messages that include information
like who it's going to, where it's coming from.
You know, you're not going to be asked too specifically
to say that, like, RETR, it's not [inaudible] it's just
like there is a message you can send that would [inaudible]
>> R.J. Aquino: So just, again, for the camera,
we have confirmation that we're really looking
for a conceptual understanding that here is what is possible,
here is the way in which it works, you know,
it's a two-way communication, in some cases;
it's a one-way communication in others.
But, you know, we're not really looking for, you know,
could you on command say RETR to get a message from a pop server.
Just understand that pop is how you get a message from a server,
and there is a command for getting a message,
but that it's RETR is not the level of detail we're hoping
that you memorize, just the overall picture.
>> Ben Shryock: Another question.
>> When you do like the mail from at the top
and then you put the username, when you go into the data
and then say mail from or from the username,
does it have to be the same?
Like, is that a way that you can fish
or like change the email address you see,
or does it need to be the same?
>> R.J. Aquino: So in the Barack Obama spoof,
was it just the second one, or was it both?
>> Ben Shryock: [Inaudible]
>> R.J. Aquino: Yeah, so when you say mail from,
the very first one, that's actually where it's coming from.
Yes, no, maybe?
Yeah.
>> [Inaudible]
>> R.J. Aquino: Right.
And the second one is the one that sort of displayed,
and it's the one that Gmail uses to sort of pre-populate
and show you where it's coming from.
And so that's how you would spoof.
They don't have to match is the short answer.
The Barack Obama spoof being an example of that.
Another question?
>> How do you blow up the screen [inaudible]
>> R.J. Aquino: Right.
So this, actually, we went into...on a Mac,
you go to the terminal.
On a Windows computer, you can go to, sort of, a command prompt
or another program like a terminal.
>> [Inaudible]
>> R.J. Aquino: Yeah, so...so the question was,
how do you get to the terminal.
The terminal is just a program on Macs in particular
that allow you to enter, sort of, commands and interface
with the computer a little more directly.
So if you...
>> Ben Shryock: I'll pull it up.
>> R.J. Aquino: If you zoom out and pull it up, yeah.
Are you going to zoom?
>> Ben Shryock: Control...cool.
>> R.J. Aquino: So if we just search for terminal
on the Mac, it will show up.
Otherwise, we can go to the applications menu.
And here we've got a full-screen terminal.
If I make it smaller...oops.
This is what you'd probably see the first time you open it,
something sort of small and with much smaller font.
And then this is for interfacing, you know,
typing commands to your computer a little more directly.
>> Ben Shryock: So when you've seen this interface in lecture,
like when Tommy did traceroute or some of the things today,
you can do the same thing if you have a Mac or a Linux just
by pulling up a terminal and running those same commands.
>> R.J. Aquino: Just to make it super clear, you wouldn't use,
sort of, Google Chrome or Safari.
Those are like the web browser
that allow you to go to Gmail.com.
If you want to do some of these more technical,
under-the-hood things, you would be in a terminal here.
Yeah?
>> Is there any way [inaudible]
>> R.J. Aquino: Yeah, so Windows PCs typically have something
called the command prompt.
>> Or DOS prompt or...
>> R.J. Aquino: Yeah, or the DOS prompt, which allows you to sort
of have a similar interface with the computer, although some
of the commands may be slightly different.
Is there a question over here?
>> [Inaudible]
>> R.J. Aquino: But in particular in the case
of this email example, we...the very first thing we did
in the terminal was ran a command like this
which the technical details don't really matter,
but we're saying is, you see in there, connect Gmail.com SMTP,
all right, among other things, so this command
to the terminal says, hey, open up a connection
to SMTP.gmail.com, and then it replies with a bunch of things,
like we went through the whole log in process.
But this is how you would,
from the terminal, start a connection.
>> Ben Shryock: Do we have any other questions
on today's material now that we know that that's fair game
for the review session?
[Background discussion]
>> R.J. Aquino: I think the most important thing we covered today
was probably memes.
[Laughter] I would study those.
They're great for procrastinating.
But in terms of other topics, we did, you know,
we prepared slides for all the things we thought you might ask
about, so we'll definitely post those.
They're useful.
They're sort of a skimmed down version of the lecture slides
so that you don't have to go through, you know,
four hundred lecture slides while trying to study.
Although you definitely, I would recommend
that you reference them.
If you're going through a recap or one of our review slides
and you find something you don't, sort of,
fully understand, you know, you can pull
up Tommy's lecture slides and dive into those.
But we'll also be posting our full review slides,
which have a section for each lecture.
We just thought it was a more useful use of time to go
over what you wanted to talk about other
than what we wanted to talk about.
Yeah?
>> Is there anything specific
with the sections you want us to know?
>> R.J. Aquino: The sections are really designed to just sort of,
you know, get more familiar with the material and also, sort of,
to explore some potential applications of material.
In terms of the exam, only lecture content, although,
feel free to watch the sections if you find them sort of useful
for synthesizing concepts and seeing a real-world example of,
you know, well, you know, what are [inaudible]
or what a motherboard is or things like that.
But the lectures in particular are the...if it's in a lecture,
it could be on the exam.
If it's in a section, it may or may not be.
Only if it was in lecture, I should say.
So...
>> Do we have any problem set
for today's lecture due next week?
>> R.J. Aquino: So did you talk about it at all?
>> So I'll send out an email on how that's going to work.
[inaudible]
>> R.J. Aquino: I can...see, I'm on mike, so...yeah,
so basically there will be...
>> Ben Shryock: Do you want a mike?
>> [Inaudible]
>> R.J. Aquino: Yeah, so they'll be a problem set released.
It won't be due until the next Monday we have lecture,
which is actually a few from now because of spring break.
But if you submit a version of it before...was is Friday?
Before Friday, we can promise qualitative, not quantitative,
but qualitative feedback for Monday,
just so that you have seen, sort of, the right
or wrong answers for the exam.
And they can resubmit before the real deadline if you so choose.
So if you happen to be able to get it in by Friday, we'll,
you know, take them in Friday, Saturday and grade them
over the weekend, so you actually can receive
that qualitative feedback because the material
on this release problem set is fair game for the exam.
So that's an offer we're making.
But the actual due date of the problem set will be the Monday
of the fifth lecture, which is March 25th, I believe,
which is reminding me how, you know,
quickly this semester has been going.
But, yeah, we have an exam this Monday,
spring break the following Monday,
and then the problem set will be due, lecture five, after that.
>> Ben Shryock: Any questions on that process?
>> R.J. Aquino: And Tommy's going
to send an email detailing all that, so don't worry
about remembering any of it, but just so you guys know.
Any other topics, things like these?
>> Just to be clear, this isn't going to be
like a problem set designed to take you three weeks.
It will still be like the same problem set that you're used to.
>> R.J. Aquino: Yeah, so Tommy said...there will be an email
anyway, but the problem set is not a three-week mega problem
set, you know, stay up all night for weeks at a time.
It's going to be a regular problem set designed
to take one week.
It's just that week happens to be a few weeks from now
as opposed to this week because we like spring break too.
Anything else?
Any other topics at all?
Any questions?
Questions for us?
Questions about...yeah?
>> I just have a question about problem set three for,
I forget what [inaudible] I couldn't figure
out why it wasn't, you know, going anywhere.
>> R.J. Aquino: So that was a question about a problem set?
>> I don't remember off the top of my head.
>> R.J. Aquino: Yeah,
Tommy doesn't remember the answer either.
It was something about where's mlb.com, sort of go to.
We can actually give it a try because we talked about that.
[Inaudible] Quick link?
Oh, it won't work here, will it, Tommy?
[Multiple background voices]
So if that's indeed the case, we'll...
[multiple background voices]
>> Ben Shryock: So for the camera,
when everyone was doing the problem set,
they got stuck in Frankfurt.
>> R.J. Aquino: That's what I'm hearing.
When I saw the problem set,
there was only cse1 and McDonalds.
>> [Inaudible]
>> R.J. Aquino: If it didn't work for the first two,
I would sort of use that as your sort
of conceptual guidance for the exam.
In terms of the third one, if something weird happened, we'll,
you know, just ignore it.
>> You had to wait for like thirty seconds
or a minute or so.
[Multiple background voices]
>> R.J. Aquino: Yeah, no, when I travel,
I tend to wait a long time in Frankfurt as well.
[Laughter]
>> Ben Shryock: All right.
So we'll stick around in case there are anymore questions.
You're welcome to come up and talk with either one of us,
but I think our formal review session is now over.
Good luck on the exam next week.
>> R.J. Aquino: Yeah, we'll see you Monday.
[ Silence ]