CIS 1110A - Computer Operating Systems and Maintenance

Module 10

This chapter discusses several unrelated subjects. Objectives important to this lesson:

1. Virtual machines
2. Cloud computing services
3. Printers
4. Networking printers, managing features, and queues
5. Supporting printers
6. Troubleshooting
7. Current assignments
   
   

Concepts:

This was probably going to be three shorter chapters, but it covers two topics we have not covered in this curriculum before, then hits some familiar material about printers. The author's first topic is virtual machines (VMs). It is common practice, for instance, to learn about a different operating system by loading it into a controlled memory space. That space is called a virtual machine. Installing an operating system in that space will allow your computer to continue to run normally, but will also allow you to do things in that space as though you were running a different computer.

Dr. Andrews mentions that there is another kind of virtualization that is used for just for applications. She promises more about this later in the chapter.

A hypervisor is the control system for virtual machines. It comes in two types.

• Type 1 (bare metal) runs as the base software on a computer. There is no actual operating system on the computer that will host the virtual machines. This is a good idea for devices that are meant only to host virtual servers.
• Type 2 (hosted hypervisor) runs as an application on top of an operating system. This is the way most classrooms and analysts use VMs. You download and install a hosted hypervisor program such as VMware or VirtualBox.This is a better approach if running a virtual machine is not the main purpose of a computer.
• VMware is available in a free version that hosts one VM at a time. It is also available in a paid version that has more features. The free version may not be used by a commercial entity.
• VirtualBox (an Oracle product) is free, and can host multiple VMs. Its limits depend on the abilities of the computer on which you have loaded it. It is easy to use and is often preferred in classrooms. Dr. Andrews presents some screen shots of VirtualBox on page 509.

An advantage to running experimental software on a virtual machine is that you can save the state of the machine at any time, making it possible to return to that moment in time before everything went wrong. (Oh, God! You loaded the October patches??) That also means you can load the same machine on different computers by putting a copy of the VM image on the next computer.

Dr. Andrews offers some advice about choosing a computer that can run VMs well:

• a VM runs best if you can dedicate one or more cores of your processor to it, so multiple cores on the host machine are preferred, along with Hardware Assisted Virtualization (HAV), which is expected on current processors but may not exist on older ones.
• a motherboard that allows HAV to be enabled
• have enough RAM to run your computer without the amount you allocate to the VM
• have a large hard drive because the VM will use a portion of it as a simulated hard drive for itself
• every VM on a computer will require "its own" access to network assets and/or the Internet, so your shared network interface needs enough bandwidth to handle the increased traffic

If you install an operating system on a VM, it is a lot like doing so on a brand new computer. If you load a working copy of a VM, that is much faster. The vendors of VM manager software often have images of major OSs available for download on their websites. Alternatively, you may find images you need on the web. ONLY use images from reputable sources!

A fair question at this point might be what is it good for? Let's try a recent video that gives us some ideas:

Page 512 takes us to cloud computing. Let's start with a definition from NIST of cloud computing:

• a computing model
• for enabling ubiquitous, convenient, on-demand network access
• to a shared pool of configurable computer resources (e.g. networks, servers, storage applications, and services)
• that can be rapidly provisioned and released
• with minimal management effort or server provider interaction
  

The bottom line is that a vendor is selling/leasing services that are available as needed from devices that are owned or operated by that vendor. It should be obvious that such a model depends heavily on reliable, fast, error free data access, typically over an Internet connection. If your business does not have access to that kind of Internet connection, cloud computing is not for you. If you have that kind of connection available, you may want to use someone's cloud.

As usual, Linus Sebastian has another insight. I kind of like his spin on the label:

Features that make cloud services attractive to a business:

• no hardware cost for the client, except for client side machines
  
• no problems when you scale up such a service, and it may scale down automatically; shared infrastructure means the client does not have to build it
  
• web interfaces may mean little software cost for the clients

Clouds come in several types:

Cloud services come in several types as well:

Service models:

The author discusses application virtualization as another service available through cloud systems. She presents two versions:

• Cloud-based applications - The user accesses a server that runs the desired application in a session on the server. This is sometimes done to avoid installing the software in many locations, or to make use of older computers that would not be able to run the desired software without access to the application server. We have done this for years in state government, but we did not call it a cloud service. As I have told other classes, there is no such thing as a cloud. It is only someone else's computer.
• Application streaming - In this case, some software stays on the web, but a connected portion of the app is pushed to the client machine, enough to enable the user to run the application.

A computer that is going to access cloud services can be set up in several ways:

• thick client - A computer that is fully functional, that can install and run most applications.
• thin client - A computer that is less functional, such as a Chromebook that is expected to run applications through a browser window. Such a computer still needs good access to the network and the internet, but may have lower level processing, storage, or memory capacity.
• zero client - A computer that does not actually run programs. These are often called dumb terminals. They contact a server that actually runs the desired programs.

On page 517, the chapter turns to the topic of printers. The section begins with a good discussion of how laser printers work. It has been reported by students taking the A+ certification test that questions on printer troubleshooting are common, so this chapter is an important one to study.

There are seven processes listed that take place when a laser printer prints:

1. Print request - A print image is sent to the printer from a computer, smart phone, or other device. (When sent through a print server, there is more to it, but the printer doesn't care.)
2. Charging/Conditioning - the drum, a rotating barrel in the printer, is given a strong, uniform electrical charge. The example in the book indicates a charge of -600 to -1000 volts.
3. Exposing/Writing - a laser changes the charge on the drum everywhere toner is meant to go. (Toner becomes ink. See below.) The charge may be -100 volts. This change effectively puts an electrical version of the print image on the drum. The change takes place only in areas that correspond to characters or images to be printed. The image on the drum is a mirror image of what is intended to print.
4. Developing - toner (powdered plastic printing powder) is given a charge in between the two charges listed above. Let's say it's about -500 volts. This charge is close enough to the -600 volts on most of the drum that those areas repel the toner. However, it is different enough from the -100 volt charge on the image areas of the drum that those areas attract the toner. Electrical differences are relative, so this works. The drum is supplied with toner and low voltage image areas become coated with it. This is the magic part.
5. Transferring - a piece of paper is given a strong positive charge, which attracts the toner more than the weak negative charge of the image area on the drum. The paper is passed close to the surface of the drum, and the toner transfers to it. Because the drum rolls along the paper, the image made by the toner is transferred to the paper. Because the drum held a mirror image of the intended print job, the toner now shows the intended image on the paper.
6. Fusing - the paper, now having toner on it, passes through heated rollers, which fuse the ink and plastic toner to the paper. This makes the image on the paper more permanent, and minimizes smearing.
7. Cleaning - the drum is cleaned of toner, and cleared of any residual electrical charge.

It is possible to carry out the processes above by reversing the charges involved. The principle works either way.

If that was too much, Linus will give it to you again.

The process above describes how a monochrome printer works. A color laser printer follows a similar process, but it uses four different colors of toner, so the Charging and Writing steps take place four times, each time placing a different color component of the image on the drum. Color laser printers generally use the CMYK (Cyan, Magenta, Yellow, and Black) color system.Why K for black? In most color systems, B stands for blue.

Common problems with laser printers are described can be simple to diagnose:

• If the output is faded, smeared, wavy, speckled, or streaked, you may be low on toner. Try shaking the cartridge to break free any toner that is caked up inside it. Replace the cartridge with a new one if possible.
• Paper will not perform well if it is too hot, too wet, too dry, too thick, too thin, or simply the wrong kind of paper. Yes, you want Goldilocks paper. Do not open packages of paper until you are ready to use them. Do not store the paper where it can become damaged by heat or moisture. Use fresh paper, of an appropriate type for the printer.
• Paper jams often occur in laser printers. A technician servicing such a printer should become familiar with the path that paper is meant to follow through the printer, and should be able to troubleshoot that path for shreds of paper that can clog it. When you see torn sheets of paper coming out of the printer, it's time to play Indiana Jones and find the missing fragments.
  
  
  
• For color laser printers, if the colors are wrong, you are probably out of one or more colors of toner.

The text mentions duplexing, which is simply printing on both sides of a piece of paper during the print job. You should now have an appreciation of how difficult that is for a laser printer.

The text also discusses several other kinds of printers:

Printer Type	What about them?	Example images
inkjets	a common home office choice; the printer is cheaper than a laser printer, but the spray-on ink cartridges can be expensive
impact printers	dot matrix printers use a set of hammers and pins to strike an ink ribbon in various patterns to form characters; some printers used hammers with characters on their ends to strike the ribbon; this is not obsolete tech: it is still the only way to print on a form with carbon paper between its pages, unless you have an actual typewriter
thermal printers	often used to print documents that are expected to be thrown away, such as receipts at a gas pump; images on thermal paper fade over time and can be ruined with heat
3D printers	a young technology that creates models from CAD images using heated resin or plastic filament; good for prototyping designs or creating custom objects (this is not really a printer, but that's what they call it)

The text continues with some ideas about adding printers to a network to be shared by multiple users. The author mentions that a printer can be shared even if it is connected directly to a computer, but this is less useful than making the printer an actual host on the a network. Physically adding a printer to the network can be simple.

• If the printer has an Ethernet card, just connect it to a nearby switch or router port with an appropriate cable.
• If necessary, set the printer to get an address from DHCP.
• If the printer has to be connected to a computer with a dedicated cord or a USB cable, it can still be shared, but the computer it is connected to must be running for the printer to be accessible. Not a good situation.
• In either case, make sure that the computer that will use the printer have appropriate printer drivers for it. The driver needs to match the printer and the OS of the computer sending the print image.

The text has two exercises that run from page 528 to page 532. Run through this section if you have a printer on your local network or one you can add to it.

On page 532, the author brings up the idea of securing a printer. This may sound odd to you, but it is not. I often use my cell phone in boring locations to look for unsecured Wi-Fi access points. Most people who hang a wireless printer on their Wi-Fi network don't consider that the printer can be a portal into their network.

There is a short section ending on page 536 that discusses printing to a file. The author remarks that this skill may be required on an A+ test.

The chapter continues with more trivia about printers. Take a look at the chapter summary for a quick dose of this information.