Time
5 hours 54 minutes
Difficulty
Intermediate
CEU/CPE
6

Video Description

This lesson discusses memory and covers the following types: • Random-access memory (RAM) o Dynamic/static o Cache • Read-only memory (ROM) • Programmable Read-Only memory (PROM) • Erasable Programmable Read-Only Memory (EPROM) • Electronically Erasable Programmable Read Only Memory (EEPROM)

Video Transcription

00:04
all right, so let's talk a little bit about memory now.
00:08
Two main types of memory that we generally think about. We think about RAM and we think about Rahm Ram is random access memory and the idea of random access. His memory doesn't have to be access sequentially, you know. Think about if you had a favorite song back in the days of eight track tapes or regular cassettes
00:27
and you wanted to play track number three, well, there was no way, really to jump straight to track number three.
00:33
You'd have to fast forward than you'd still being tracked to the *** Fast Fords. More now your track floor, you have to kind of back and forth. There was no easy way to go to a specific line of a song, for instance. Well, with random access, you can access any address, any piece of information that's in RAM.
00:52
So obviously that's very beneficial for us.
00:54
Now, when people talk about system memory, they're talking about RAM, and specifically they're usually talking about your dynamic ram, your D Graham system. Ram is dynamic in nature and with dynamic in nature, it means it's frequently changing
01:11
the contents of Ram have to constantly be refreshed. They don't hold their contents very long.
01:17
We talk about Rand being very, very volatile because if there's a loss of power to Graham, all the contents of RAM are immediately a race. So when we talk about volatile versus non volatile, it's all about Do they require that constant source of power and with dynamic ram? Yes, that system memory.
01:38
But there's also a type of much more expensive RAM called static RAM
01:42
that holds its contents holds its charge much longer does not have to constantly be refreshed.
01:49
This type of memory is used for cash,
01:53
and any time we talk about cash, cash is always gonna have the same purpose. Cash is always gonna be about,
02:00
um,
02:01
a location for things that are requested frequently
02:06
to speed up that requests the next time. That way they happen. I mentioned the CPU registers a little bit earlier. That's high speed cache. There's also cash built onto the processor. There's cash built onto the motherboard. There's all types of virtual cash written into applications,
02:23
so cash is always about the idea of let's have a place to store things
02:29
that we anticipate needing to use. So cash is gonna be static ram, and it speeds things up tremendously. As a matter of fact,
02:39
uh, the way cash works because it's able to hold those contents were before so much longer without having to be refreshed. It's because of the fact that they're just millions of transistors involved with static cash.
02:55
Because of that, static cash is really expensive. And to give you an idea of how expensive is if you go back several years ago and I used to build my own computers, and I used to be a lot more involved with hardware than I am now. And one of the things that I used to remember is in building a system and choosing processors.
03:14
There were two choices from it and from Intel.
03:17
You had the Pentium chip and you had the Celeron ship.
03:21
Now, many people were confused with the difference because you'd see a penny, um, 9 33 system and you'd see in a Celeron 9 33 system. They both had the same speed at which they operated, but the Celeron processor
03:37
would be 100 $125 less than the pinion chip.
03:42
Why
03:43
the difference between the Celeron chip in the Pentium chip was simply the difference between ah 128 megs of onboard cash and 512 megs of onboard cash that came with the pinning him.
03:57
So the Celeron had less onboard cash, but only by 384 megs. That's not a lot by today's standards. Just those 384 megs of cash justified increasing the cost of the system over $100. So static
04:15
cash or static ram, which is cash,
04:17
is very, very expensive. That's why we don't use it for system memory. All right, so that's RAM. And we could go into all sorts of different types of Ram, DDR, RAM and all those things were not going to get that specific lots of different flavors of Ram today.
04:38
What we are gonna look at now, though, is read only memory wrong and ideally, with redoubling memory. This is memory that can be written to one time on Lee. So, of course, with your CD ROM's that it's written to, and then you can read the contents of the CD room, but you can't write to it
04:57
well, chips on the motherboard. At one point in time. We're Rama's well, and you might have very, very basic instructions on the board through these chips. And those instructions couldn't be modified.
05:08
Maybe the system BIOS was written to RAM and would not be modified.
05:14
Well, the problem with that is, as the architecture of the system changes and as we may want to upgrade the system, we need a BIOS that's flexible.
05:24
So originally we went from Rahm, read only to something called prom
05:30
programmable read only that still wasn't flexible enough. So the next move we made was erase herbal programmable read only memory. And what this allows us to do is on the the little chip for Rahm for your system bios, for instance,
05:48
there was a little sticky tape, almost that you could pull back,
05:54
and you could expose the bio ship to UV light. And you could actually rewrite elements of the bios using that technique. And that technique was referred to his flashing the bias because you were exposing it to UV light.
06:08
So now, today, when people talk about flashing the bios, that's what they mean. They mean upgrading the processor, but what you'll see is because again, that was so very cumbersome. We found an easier way to upgrade the BIOS, and that's through electronically. Erase. A ble program will read only memory
06:27
e crop, and that's almost assuredly what most devices air using today,
06:31
which simply means we can use software. We can run a program off of a thumb driver off of a disc that allows us to flash the BIOS or to upgrade the Brian the BIOS using software. That's a great news. We can update the virus using software. That's bad news.
06:49
The bad guys can update our bias using side software.
06:53
So we have to be very thoughtful about that, because once our bios becomes corrupted that our system is corrupted. So we always want to be very mindful about how improvements for performance and cost, and and all those other ways we look to improve. Our system can also be used by the bad guys
07:12
to further jumper minds.
07:14
All right, so that's a look. A memory within a system

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