Computer Applications

Modern electronics work happens around computers — they run test equipment, store service data, control instruments, and are themselves the device under repair. The Associate CET exam expects familiarity with the building blocks: how a computer is organized, the kinds of memory, the ports that connect equipment, and the key computer and networking terms. It also covers how a computer starts and runs programs, installing and configuring one, loading and storing programs, utilities, backups, surges and viruses, Internet access and cybersecurity, downloading safely, and stand-alone versus networked computers.

How a computer is organized

At the block-diagram level every computer is the same: a CPU (the processor) fetches instructions and data from memory over a set of shared wires called buses, processes them, and exchanges data with the outside world through input/output (I/O) ports. The same fetch-process-store cycle underlies everything from a microcontroller to a desktop.

Bits, bytes & binary

Computers represent everything — numbers, characters, instructions — as combinations of binary 0s and 1s. A single 0/1 is a bit; 8 bits make a byte. The number of distinct values a group of bits can represent is 2 raised to the number of bits, so an 8-bit code gives 2⁸ = 256 combinations.i2ⁿ combinations: each added bit doubles the possibilities. 4 bits = 16, 8 bits = 256, 16 bits = 65,536. This is why memory and addresses come in powers of two.

Types of memory

The single most-tested computer concept is the difference between the two main memory types:

Ports & interfaces

Connecting equipment to a computer is everyday technician work. The dominant modern interface is USB (Universal Serial Bus); older equipment used the parallel "Centronics" printer port and serial (RS-232) ports.

Every device on these ports is a peripheral: an input, output or storage device outside the CPU and memory. The Computer Electronics guide's section 11 defines peripherals and the interface cards and chips behind the ports (competencies 15.8 and 15.9).

Software & the operating system

Key terms

Computers as test tools

Beyond being a repair subject, computers are instruments: PC-based oscilloscopes and logic analyzers, software that logs meter readings, and control of bench equipment over USB or Ethernet. An analog-to-digital converter (ADC) is the bridge — it samples a real-world analog voltage and converts it to the binary values software can store and display. When equipment is software-controlled, troubleshooting may require a computer to read its diagnostics.

Basic operation: from power-on to a running program

Competency 16.1 asks you to explain basic computer operation. When the power comes on, main memory holds no software, so the CPU first runs the firmware (BIOS or UEFI) stored in ROM or flash. From there the start-up runs in this order (Wikipedia, Booting):

1. Power-on self-test. The firmware runs the POST, which checks and initializes the hardware, such as main memory.
2. Boot device. It works through its boot order, a list of storage devices you can set in the firmware's setup screen, until it finds one it can start from.
3. Operating system. A boot loader on that drive loads the operating system from storage into RAM, and the OS takes over the hardware (section 5).
4. Programs. Each time you start a program, the OS loads it from storage into RAM and the CPU runs it from there (section 11). Your work stays in RAM until you save it to storage.

Installing and setting up a computer

Competency 16.2 asks you to explain the steps in the installation and set-up of a computer. The order matters most for security: a new computer should be protected before it first goes online. CISA's advice for a new computer is in steps 4 to 6 (CISA, Before You Connect a New Computer to the Internet).

1. Unpack and inspect. Check for shipping damage and follow the maker's set-up guide. Handle boards, memory and cards with ESD precautions (Safety guide, section 5).
2. Connect. Connect the monitor, keyboard and other peripherals (section 4), and plug in through a surge protector or UPS (section 14). Leave the network cable unplugged for now.
3. Install the software base. Install or finish setting up the operating system, then the device drivers for its hardware, which let the OS control each device (section 5).
4. Protect it before going online. Secure the router (section 15); turn on and configure the firewall, and protect its settings with a strong password; install antivirus software; then connect to the network and let it update itself.
5. Update. Install all available updates from the software vendors, then turn on automatic updates.
6. Set up the accounts. Use a standard account for everyday work and the administrator account only when needed (least privilege), and remove software and default features you do not need.
7. Test. Check that every peripheral works, the network connects, and a first backup runs (section 13).

Configuring a computer: reasons and choices

Competency 16.3 asks you to explain the reasons and choices used in configuring a computer. Configuring means setting a machine up for its job and its user; each choice below has a reason behind it.

Loading and storing programs and data

Competency 16.4 asks you to describe proper loading and storage of common programs and applications. Programs and files are stored on mass storage, the hard drive or SSD, which keeps them with the power off. To run a program, the operating system's loader brings it from storage into RAM, where the CPU works on it (Wikipedia, Loader). What you are working on stays in RAM until you save it, and RAM is volatile (section 3), so unsaved work is lost when the power fails.

Utility software

Competency 16.5 asks you to explain basic common utility software and list the reasons for its use. Utility software supports managing the computer itself, rather than doing the user's work (Wikipedia, Utility software).

Backing up data

Competency 16.6 asks you to list ways to back up data and explain the vital importance of doing so. A backup is a second copy you can recover from when a drive fails, malware damages or locks the files, or someone deletes them. A backup on the same internal drive is lost with that drive (US-CERT, Data Backup Options).

The copies can go on external hard drives, USB flash drives, SD cards and SSDs, optical discs, tape, or remote (cloud) storage. US-CERT's 3-2-1 rule: keep 3 copies of any important file (the original and 2 backups), on 2 different types of media, with 1 copy off-site. Keeping a backup physically separate from the computer protects it from online attackers and power surges. CISA adds: keep offline, encrypted backups, and regularly test that they are available and can be restored (CISA, #StopRansomware Guide).

Line surges and viruses

Competency 16.7 asks you to explain the causes of line surges and viruses and the protection procedures against each. Surges come from two sources (NIST, Surges Happen!, SP 960-6): lightning, by a direct strike or by the voltage a nearby strike induces in power, telephone and cable-TV lines; and switching, when electrical loads are turned on or off inside the building or by the utility's own operations. Every wire into the equipment, whether power, telephone, cable, antenna or network, is a path a surge can follow. A surge protector does not stop a surge: it diverts it to ground. Choose one listed by a testing laboratory such as UL, ETL or CSA, and protect the telephone, cable and network lines into a computer as well as its power. A UPS covers an outage: its battery typically runs the load for 5 to 15 minutes, long enough to shut the computer down safely, and most units also give surge protection (Wikipedia, Uninterruptible power supply).

Malware is unwanted software that can harm a computer or compromise its data. A virus can damage or destroy files; a worm spreads itself from computer to computer; a Trojan horse is a program that hides a virus or other harmful code. They spread through infected removable media, malicious email attachments and links, and harmful downloads (CISA, Protecting Against Malicious Code), including bogus ads for software (FTC).

Getting on the Internet, and cybersecurity

Competency 16.8 asks you to explain how to access the Internet, cybersecurity best practices and common applications. A home or small-office connection runs from the Internet service provider's line to a modem (DSL, cable or fiber) and on to a router, often in the same box. A modem only carries the signal over the line; the router joins the local network (LAN) to the provider's wide area network, translates addresses (NAT), hands out IP addresses by DHCP, acts as a firewall and usually provides Wi-Fi (Wikipedia, Residential gateway). The common applications on top are the web browser, email and file transfer (FTP, section 6).

Downloading software and data safely

Competency 16.9 asks you to describe how to download a service or application, data or software. Downloads are one of the main ways malware gets in (section 14), so the method is mostly about the source and about checking the file:

1. Go to the source. Get it from the maker's own website, reached by typing its address yourself, or from a store you trust. Do not download from an ad, a pop-up, or an unfamiliar site offering free downloads (FTC, How To Recognize, Remove, and Avoid Malware).
2. Check that it fits. Choose the version for your operating system and hardware, and read the maker's requirements before you download.
3. Verify the file. If the maker publishes a hash (a SHA-2 value such as SHA-256), compute the downloaded file's hash and compare: a match means the file arrived unchanged (Wikipedia, File verification). A digital signature (code signing) shows who published it and that it has not been altered since; the operating system warns before running unsigned software (Wikipedia, Code signing).
4. Scan it. Let security software scan the new file before you open it (FTC).
5. Install and keep it current. Use the administrator account only for the installation, then turn on the program's automatic updates (CISA, NCSC).

Data such as service manuals and firmware files follows the same rules. A service you sign up for online, such as cloud storage, is not downloaded at all: create the account on the provider's own site and protect it with a strong password and multifactor authentication (section 15).

Stand-alone and networked computers

Competency 16.10 asks you to explain the differences between an individual stand-alone computer and basic networking. A stand-alone computer works only with what is attached to it; a networked computer shares data and resources with other computers.

A LAN (local area network) links computers that are physically close, in one home, office or building; a WAN (wide area network) spans regions, countries or the world, and the Internet can be considered one (Wikipedia, Wide area network). On a client-server network, a server provides files or services to many clients from one central place; on a peer-to-peer network, the computers are equals that share with each other directly (Wikipedia, Client-server model).