Tape drives are a critical component of today’s PCs because they provide a way to back up the data stored on a hard drive. If the data on the hard drive has been backed up on a tape drive and the hard drive fails, the hard drive can be replaced and the operating system, applications, and data files restored from the tape backup unit.
Tape drives work in the same way that a cassette tape recorder does — or more to the point, like a digital audiotape (DAT) does. When you insert a tape cartridge into the tape drive, you can then copy the digital data stored on the hard drive to the tape cartridge. The information is fed across a magnetic head in the tape drive.
Backing up data is primarily the responsibility of the system administrator, but a service technician should verify that the data on the hard drive has been backed up before replacing a hard drive.
Not all data is copied from hard drive to tape backup each time a backup is performed. When a file is backed up, the archive attribute for that file is turned off. When the file is modified and saved by the operating system or application, the archive attribute is turned back on. The tape backup application can look at the attribute for a file and see whether the file was modified since the last backup; if the file hasn’t changed, it doesn’t need to be backed up.
Some of the more common types of backups that are performed and that use the archive attribute are listed below.
Full backup — A full backup backs up all the data on the hard drive, whether or not the archive attribute is set. After the backup is run, the archive bit is turned off.
Incremental backup — An incremental backup backs up only the files that have changed since the last full backup was performed. An incremental backup knows which files have changed by reading the archive attribute. After an incremental backup is run, the archive attribute is turned off.
Differential backup — A differential backup backs up the files that have changed since the last backup but does not reset the archive attribute after the backup is run.
Note: Data transferred to tape can also be compressed so that each tape can hold more data.
COMPUTER PERIPHERALS
Monitor
Keyboard
Pointing device
Joystick
Computer peripherals are attached components that are not part of the core components of the PC. Peripherals provide the PC with enhanced capabilities. Some of the different peripheral devices are discussed below.
Monitor
The monitor receives input from the video adapter card and displays that information on the screen. MDA, CGA, and EGA monitors receive digital information from the video card and are connected to the PC with the 9-pin, 2-row connector. VGA monitors receive analog information for the video card and are connected to the PC with a 15-pin, 3-row connector (Figure 2.6).
Notebook computers come with a mono or color Liquid Crystal Display (LCD) panel that takes the place of the monitor, though you can also connect an external monitor to the notebook computer.
One of the newest products is a color LCD monitor for desktops. These monitors are very expensive, up to two times the price of a regular monitor.
Keyboard
In command-line operating systems, the keyboard is the main interface the user has to communicate with the operating system. With the advent of the GUI operating system, the keyboard shares this responsibility with the mouse or other pointing device.
The original PC keyboard had 84 keys. Keys have been added so that today’s keyboards provide more than 100 keys to the user. The 101-key keyboard is the most common.
The keyboard is connected to the motherboard with either a DIN-type connector, known as an AT-style connector, or a PS/2 style mini-DIN connector (Figure 2.7).
Pointing Device
The first pointing device used on IBM-compatible computers was a two-button mouse that was introduced with Microsoft Windows. Some of the other pointing devices are three-button mice, trackballs, light pens, and data tablets. Figure 2.8 shows a mouse and a connector.
You can connect pointing devices to the PC through one of the PC’s serial ports or through a PS/2 mouse connector.
Joystick
Joysticks are another input device for PCs. Today, joysticks are typically used only with computer games. The joystick is connected to the PC through a 15-pin, 2-row connector, as shown in Figure 2.9.
REVIEW
The focus of this chapter was to provide a closer look at the core components of a PC and explain a number of new terms that are associated with recent technology improvements.
The case provides a protective cover for the internal components of PC and also provides an enclosed, safe working environment for the internal components.
The power supply has two major functions: to provide power to all the internal components of the PC and to pull hot air from the case’s air plenum and force it out the rear of the case with the help of a built-in fan.
The motherboard is the large circuit board mounted to the bottom of the case and provides all the connections for the components of the PC. Two integral components of the motherboard are the CMOS chip and the BIOS chip. The CMOS chip is powered by a small battery and stores the time, date, and configuration information for the PC. The BIOS chip permanently stores the POST and a basic communications program that is loaded during the boot process. The motherboard also has a custom socket for the processor chip, custom sockets for RAM, and at least one external bus for interface cards.
The processor is the “brain” of the computer. Some of the CPU chips used are the 8088, 80286, 80386, 80486, and Pentium processor. Only certain processors fit on certain boards. The socket on the motherboard can be used to determine what type of processors can be used.
RAM is the working, volatile memory area of the operating system. Applications and data reside in RAM while being processed. RAM is volatile because the data stored in RAM is lost when power is removed from the system. Some of the different memory packages used on PC motherboards include 30-pin and 72-pin SIMMs and 168-pin DIMMs. Memory is arranged into banks for access by the processor. Banking allows the processor to access more than one row of memory at a time.
The external bus provides sockets into which I/O cards are plugged. The different external buses available in IBM-compatible PCs are the 8-bit and 16-bit ISA bus, EISA bus, VL bus, and PCI bus. The PCI bus is the most recently released and popular bus.
Hard drives and hard-drive technology have changed dramatically since the introduction of the PC. Two different schemes for encoding data onto the hard drive have been used with PCs. The first is MFM, which is still used for floppy disks, and the second is RLL, which is still used for hard drives. The first PC hard drives used the MFM encoding scheme; the drive technology used in PCs was the RLL drive. The RLL drives appeared physically the same as the MFM drives, but provided 50 percent more data storage capacity. SCSI drives were next and were faster, provided more capacity, and were more reliable. However, they are quite expensive. ESDI drives were presented as a reasonable alternative, but never got a firm hold in the industry because the IDE drive was introduced shortly after their arrival and provide very cheap, fast, reliable hard drive storage.
The topics covered in this chapter and the next chapter present more than half of the terminology and topics covered on the CompTIA A+ Certification exam. Be sure you have a firm understanding of the topics covered in this chapter.
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