- When you press the power button on your computer to start it, the first thing that takes place is the power supply begins to supply power to all the different parts of your computer. Now, the trick here is that there's really no start button. We can turn the system on, but in order to get the brains, the CPU cooking, there is a wire that runs from the power supply to the CPU called power-good. When power-good reaches a certain voltage, suddenly, the CPU is started, and that's why your computer doesn't have a start button, you just turn it on and it starts.
So, when that takes place, the first thing the CPU, in turn does, is he begins a system called the power-on-self-test, or POST. In essence, the CPU goes out, all through the motherboard and makes a big announcement saying, "If you can hear me, check yourself out." And all the different peripherals go through a process, whatever that particular process that peripheral needs to do to verify that it's in good order and if it's in good shape, it reports back to the CPU, "Okay".
And if it's not in good shape, it reports back and says, "I have a problem", and that's what the POST is all about. So, the POST is taking place before anything shows up on your screen, and it's also the first thing that shows up on your screen as you boot your computer up. Now, I want you to think about this for a minute. One of the things that POST has to test is the video itself. What if there are things that are so low level that the system can't even show it on the video yet because the video hasn't been tested yet? Well, in that case, we end up having to do something called "beep codes".
So, what I wanna do is, basically, break POST into two pieces. Before the video is tested and after the video is tested. So, to begin this process, what I wanna do, and I wanna take advantage of this very, very powerful system here, this is a great system to teach about POST. To show you all that POST can do. So, let's start off with a couple of beeps. Now, to do this, what I've done is, I've set my computer up so that it has a little problem. Basically, I messed up with the video card a little bit. So, I'm gonna restart it, and I want you to listen.
This is gonna take a second, so hang on. All right, now, I wanna make this computer beep. Now, in order for it to beep, first, I need a speaker, right? So, what I have here, they call it a little piezoelectric speaker. And pretty much, every motherboard in existence has a place to plug one of these in. Interestingly enough, this particular case, which is a very modern case didn't come with a speaker, so I actually had to pull one out of another system and put it in here. POST beep codes have been around for many decades.
They were with the original IBM PC. The problem with beep codes is that you have different BIOS manufacturers out there, and even within the same BIOS manufacturer, you have alternatives to the beeps themselves. So, going back 30 years ago, there were these huge complicated series of beeps. Almost like Morse code for hundreds of different things that could possibly go wrong before your video was tested. Today, we're down to pretty much, "You don't have a "video card in" beep.
So, to make this beep code happen, I'm gonna take out my video card. And let's fire this guy up. (electrical beeps) And that is about the only true beep code that's left in your computer anymore.
By the way, that second beep that you heard, that single beep, most computers beep once, to let you know that they've booted up properly. So, if you've got a computer, and you always hear a little "chirp", that is your computer booting up properly. Also, keep in mind that this has nothing to do with your regular sound system speakers. This has nothing to do with those nice speakers and subwoofer that you have underneath your computer. This is a totally different animal, and this is something I always keep in my toolkit as well. So, anyway, that is a video card beep code, and obviously, if the video card isn't working, you can't put that out through the monitor, so you do it through a beep.
So, that is a very, very typical beep. There's only, really one more beep code that's common at all anymore, and that is, and it's not even really a beep code. It's when you don't have RAM properly installed. If you don't have any RAM in your system, in essence, your computer will make this very strange "Be-ee-ee-ee", and it will keep going forever and ever. Notice that this beep code stopped? But if you get that ongoing, almost siren-like sound coming out of this little speaker, it's because your computer doesn't see any RAM.
So, that's about all that's left in terms of beep codes. Beep codes are great, but sometimes, you fire up a computer and just, like, nothing happens. That could be pretty scary. Especially when it's on a new installation where the first time you've dropped in a new CPU and you've popped in some RAM and you plug in a power supply, and you just boot the system up to see what happens. When that takes place, you're gonna have to use something called a POST card, Power on self-test card. A POST card is something you can snap into your computer and it has two digit readouts and it's in hexidecimal.
What these actual readouts mean vary from one BIOS to the next, but when you've got a dead system, and I mean D-E-A-D, dead, no beeps, nothing showing up on the screen, the fan's turning, but nobody's home, kind of situation, POST card can be your best friend. Now, on this amazing system right here, I actually have what's becoming more and more popular on high-end motherboards, a built-in POST card. What I wanna do is, watch on the motherboard here. It's got this built-in POST card. I'm go ahead and start this system up.
Now, you can actually see it going through the POST. Each two-digit code is a step in the POST itself. So, let's see if we can get an error to pop here. (electronic beep) Okay. (electronic repeating beeps) There we go, A2, and then it's going to go ahead and try to boot up anyway. So, then it goes to AE. I think it's really cool that this motherboard has a built-in POST card, but don't panic if you don't have one.
They're inexpensive to buy, they're under 100 bucks, and you can get them at any good computer supply store, or you can find them online. I do wanna warn you one thing about POST cards. There are companies out there who will sell you, basically, a POST card with a couple of little probes on it for, like, $700, they're a waste of money. If you spend more than, maybe about 100 bucks tops, for a POST card, you're spending too much. So, keep it under 100 bucks, find a good POST card, you'll be happy. The trick with the POST cards is knowing what all of these different codes mean, because it varies from one BIOS maker to another.
There are three BIOS makers out there, there is Phoenix, there's Award, and there's American Megatrends. And actually, Award was bought by Phoenix like 15 years ago. Although, they still carry both names. Within that, there are individual versions of BIOS. You can actually tell what version of BIOS you have during the POST process, when it comes up on screen. You can use that information, go online and you can find the beep codes, as well as the POST error codes for that particular BIOS.
Otherwise, you're gonna have to try to reference the motherboard book, call the manufacturer, do whatever you need to do, but when it comes to POST codes in particular, they vary dramatically, not only between brands of BIOS, but even between individual versions. So, you're gonna have to take your time with that. Okay, well, what I'm gonna do now is, we're gonna go ahead and get everything running pretty well and we're gonna have something pop up on screen now, and let's show you the last part of POST, and that is the on-screen errors.
Okay, so what I've done here is, I've booted up the system and I've actually frozen the boot process, and I wanted you to see the POST on screen. Now, if you don't see something like this on your screen, don't be afraid. A lot of newer BIOSes will put up a big, pretty splash screen, it might say something like Dell, or Asus, or something like that. And you can actually make that splash screen go away by hitting tab or escape, it depends on your particular BIOS, but you can see this screen. Now, there's a lot of stuff going on in here, and I want you to see it.
Well, first of all, we can see the manufacturer, so we know what brand of BIOS we have. Notice that we've got a RAM count, it shows that I've got 16 gigabytes of RAM. And we also see the exact model of BIOS. So, that string of letters and numbers, and all that goobity-gag right there, tells us exactly what version of BIOS we have. So, there's a lot of good information here, but what I want you to concentrate on right now is, the fact that it looks like I've got some kind of problem with my CPU.
And that's the last type of POST error, and these are the ones that literally just pop up on the screen. Now, you've got a choice. When you get errors like this, one of two things can happen. And you can actually go into your system set up and configure this. You can do a halt on all errors, or may press F1 to continue or you can just have them go right through it. This particular error is showing up on my system because I've installed a liquid cooling system that this motherboard doesn't like, and I haven't quite figured out how to take care of all this.
The bottom line is, my CPU fan is running find, so I've gone in and I just go ahead and let it boot up right past this. POST is your best friend in the entire universe when it comes to diagnosing computers. Number one, you've got your beep codes, number two, you've got POST cards, and number three, you've got on-screen stuff. Remember, nothing's gonna show up on screen until the video's been tested. So, if your video card isn't working, you haven't missed anything that's gonna be showing up on the screen, because it's gonna be manifesting through beep codes, or you're gonna have to be pulling out a POST card.
By the way, get yourself a POST card. It's, like, nerd requirement number 223. (upbeat music)
The CompTIA A+ 220-901 exam is comprised of six key parts. The first, core processing, is covered by this course. Instructor Mike Meyers explains the fundamentals of PCs, microprocessors, RAM, and BIOS. He also shows you how to set up, connect, maintain, and troubleshoot the main components of a computer.
Note: The six courses designed for the CompTIA A+ (220-901) exam preparation include core processing, core hardware, peripherals and building a PC, displays and printers, networking, and laptops and mobile devices.
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- How do personal computers (PCs) work?
- What is a central processing unit (CPU)?
- When is random access memory (RAM) used?
- What is a basic input/output system (BIOS)?
- Installing a CPU
- Working with extensions and sockets
- Troubleshooting RAM
- Setting up a BIOS