Join Steve Fullmer for an in-depth discussion in this video Operating systems, part of CompTIA A+ Exam Prep (220-802).
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As we break into the material for the 802 exam, compTIA A+ 802 exam, when we break into the first section, one third of the exam, remember, is related to operating systems, so let's get a basic overview. Remember, when we look at hardware, hardware has dramatically evolved since the very first of our computer motherboards and/or systems. We started with chips, like this erasable, programmable, read-only memory, where we actually burned into it the binary code for the operating system. Over time, as the motherboard evolved, we went from just having a simple CPU and a real simple bios, to now having a more complicated infrastructure that includes the north bridge chip set that helps us to integrate input and output to memory, advanced graphic adapters, PCI ports, and the CPU, effectively grabbing and preloading content for the CPU's calculation.
We also have the south bridge chip set that's talking to the north bridge chip set and to our other PCI communication or PCI e-communication expanse and slots. Bios is typically fed through the south bridge, through the north bridge, and CPU. Remember the layout, the bus structure of the motherboard, allows the electronic signal to be pushed through, that allows us to use binary code in our mother motherboards. Well, just like the evolution of the motherboard, the operating system has evolved as well.
The earliest operating systems on personal computers were the disc operating systems, and most of those PCs had a total of only one megabyte, not gigabyte, but one megabyte of RAM. And so we would load DOS, the disc operating system, and that first 640kb, thousand bits, of information, and the space between 640 and one megabyte was called upper RAM, and it's where you would install bios in some of your specific hardware settings. Remember when the bios was loaded, it required specific memory locations.
What we would talk about loading is, we're actually going to load the bios, and we're going to load essentially areas, one specific memory address or location, that I would use to store content that I would use for IO back and forth between each of the devices, and so this is kind of a way to look at the way the memory is loaded. Well, taking this to the operating system level, essentially the operating system is loaded into a part of memory, but a portion of memory has to be reserved for the hardware drivers, or those interrupt areas in memory, where essentially I'm doing content back and forth.
As we expand the capability of motherboards to have more RAM, and we expand to have the north bridge and south bridge chip sets, what we end up doing is moving the locations in RAM where I'm going to store content. Clearly we've got well beyond one megabyte. 512 megabytes has been really common since the XP days for operating systems, and we're now into the multiple gigabyte ranges would go up here. A 32 bit processor can address up to four gigabytes of RAM, and so much, much larger.
As we also expand the system, there's a tendency for the bios to be rewritten or redesigned to accommodate the facilities that the south bridge and north bridge chip set provides. So if you go out and you wikipedia different layouts or boot processes and where content is stored in RAM, you'll see that it tends to, to some degree, shift around. We tend to put bios and a lot of our hardware abstraction layer, that's this, right here, this hal, hardware abstraction layer addresses in specific areas of RAM that do not move.
In that way, the north bridge and south bridge chip set know exactly where content's to be placed and retrieved, and as opposed to it being programmed, it's hard coded into the chip set that's on the mother board. And so once that design's been placed into the north bridge and south bridge chip set for particular memory locations, we don't change it without significant evolution of the hardware or the firmware that's actually designed in there by the manufacturers. So, we effectively have this low order part of the memory that's now stored for what we call page tables, and we'll describe that in another couple of slides.
We then have a specific area of memory, typically your direct memory access memory, that's at the upper end of that 640kb, and we go back to taking a look at that memory we're talking about. Remember direct memory accesses our ability for like AGP and PCI to talk to the memory directly, and those are the memory addresses that are stored in there. Bios is typically stored right up here to this boundary of one megabyte, and so it's stored from the top kind of down from there. We might also have video RAM allocated on some devices, laptops and other portables, where they need an area that's dedicated specifically to the RAM capability for the video, at least the early RAM video on smaller devices.
One megabyte. Not gigabyte. One megabyte. That's a small amount of RAM. And so, as we move to more and more RAM as that default on our operating systems and a requirement for operating systems, a lot of these addresses get pushed up as fixed locations on RAM, but after we've loaded our memory addresses and our bios, we load the kernel. The kernel is the core of the operating system. It helps us to understand, what are the components, whether they're other drivers, other services the operating system loads, we'll go into detail what a service is, and/or the applications that we're going to load on top of it in the interface to that.
When we load the windows XP operating system, we load the component called the NT executive. When we load unix operating system, vista, or windows 7, we load other components that are referred to as shells, and they get a certain area of memory, and at that higher order memory, and the upper memory, as it's available, we will load applications, and so it's a layered concept in terms of how all of our operating systems work. So, we're going to preload the system in a particular process. We're then going to assign specific areas of RAM to contain the code for various parts of the operating system, applications, drivers, et cetera, and so it's this layered concept that occurs to us.
We also cannot fit everything into RAM, whether we have four gigabytes or in a 64 bit system maybe, up to 192 gigabytes of RAM. We don't have the ability to store all of the applications and leave them in RAM the entire time. While our bios stays put and our hardware abstraction layer, hardware device drivers stay put in RAM, for the most part. Alright. Our applications of the shells that we're using, and some of the components of the operating system, are going to get swapped in and out.
We call that paging. That's the way that we can use various aspects of RAM for different purposes through different uses of the system, different boot processes, or different functionality. And so, we'll talk about a page file, or the operating system. This is the more typical way that you might see a drawing, where we're just talking specifically about the load of the content, CPU memory and devices that get loaded from our post, power on self test, and then our boot loaded, or bios processes.
That's going to load information about the CPU, memory and devices that are hardware based into the system. We then have the ability to load the kernel of one or more operating systems, not simultaneously, but several different operating systems could be loaded onto a single work station, to a single PC, so that I might boot, on some PCs and to XP, I could multi or dual boot then into windows vista or even windows 7 or maybe even a unix system, depending on how I set up the bootstrap and the hardware of that particular device.
So remember, CPU, memory and devices are very hardware based on a particular system unit that I've got, but the kernel, or the operating system is different, and then above the kernel or the operating system, we load applications, or application interfaces. So this is what we'll talk about when we talk generally about loading operating systems, the operating system model of load, for the compTIA exam. We talked about this concept of paging, so let me give you a quick overview of this concept of paging.
Well, parts of the kernel, or parts of the services associated with the kernel, or parts of the applications, won't resolve, I'm sorry, won't stay resonant in memory all of the time. As I need to use one application, and then I switch to a window from another application, then my CPU is doing other processing in the background, I'm limited to the amount of RAM installed on the motherboard, and so I essentially swap content out, that content is being swapped in and out by the design or architecture of my operating system.
That includes the north bridge, south bridge chip and the CPU, and we refer to that as paging, and so we're going to take a specific area of memory, a specific address out of memory of a particular size, and we're going to essentially swap that application that's running, but I need the RAM to be used for another application, I'm going to temporarily swap it out to an area of the hard drive that we call virtual memory or a page file, and it's actually a file that's called page file dot cis in the windows operating system.
It's a fixed, continuous component of the hard drive that's locked in place so that it's always present in one location for your system to swap in and out content from RAM as it needs it, and so we are IO bound in terms of our performance from the perspective that when I need more room in RAM for a particular application or a service to run, I will swap some content that's in RAM to this virtual memory or page file, and then as I need to use that code, I'll swap something else out of RAM into the page file, and I will swap the other content back into the space.
So this is how we use RAM when we are limited or constrained by the amount of RAM in our system, and how the operating system works. All of the operating systems that we're talking about currently today, windows XP, windows vista, windows 7, and the unix flavors the operating system you'll support on a typical personal computer, use this concept paging, or page files, to swap content in and out. As we move through the modules, talking about the operating system and the differences between them and the load, this will start to become important because you have to have a page file size that sufficient to handle swaps in and out of RAM and having enough room for the kernel to operate as well so that the kernel and applications can swap in and out efficiently as the software the operating system is designed.
It also has to do with the boot process we follow and the locations in RAM that are used by the various boot processes so that we have sufficient RAM in our operating system, in our system unit, to support a particular operating system so that we can load hardware drivers on the right sequence with sufficient space and RAM for those, load the kernel, which will change in size as we add additional functionality, and then add either the NT executive of XP, shells that are typical of vista or windows 7, or applications on top of those shells in the various operating systems.
So there's an overview of some of the terminology and the layout and the load process, in a generic sense, of operating systems for the 802 exam.
- Install and configure Microsoft Windows XP, Windows Vista, and Windows 7
- Manage and optimize Windows using command-line tools and administrative consoles
- Configure and manage users, groups, and shared resources in a typical small home/small office (SOHO) network
- Use antivirus tools to prevent and recover from malware infections
- Configure access control measures, such as authentication, security policy, encryption, and firewalls
- Diagnose and resolve Windows, PC hardware, network, and printer problems
- Configure mobile devices, such as smartphones and tablet
By the end of the course, you'll be better prepared to take the A+ Practical Application exam.
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