UPMSP Computer Technology and Maintenance cheat sheet

Data units: 1 nibble = 4 bits, 1 byte = 8 bits, 1 KB = 1024 bytes, 1 MB = 1024 KB, 1 GB = 1024 MB, 1 TB = 1024 GB.

Positional value: in base b, the digit at position n (counting from 0 at the right) has weight b^n; binary 1011 = 8+0+2+1 = 11.

Decimal to binary: divide repeatedly by 2 and read remainders bottom-up; to convert to octal or hex, group binary bits in 3s or 4s from the right.

Hex digits A-F equal 10-15; one hex digit maps to exactly 4 binary bits, so 2F(hex) = 0010 1111 = 47 decimal.

1's complement inverts every bit; 2's complement = 1's complement + 1, used to represent negatives so subtraction becomes addition.

Signed 8-bit range with 2's complement is -128 to +127; the leftmost bit is the sign bit (1 = negative).

ASCII is a 7-bit code (128 characters); extended ASCII uses 8 bits (256); Unicode/UTF-8 handles multilingual text.

Logic gates: AND outputs 1 only if all inputs are 1; OR outputs 1 if any input is 1; NOT inverts; XOR outputs 1 only for odd number of 1s.

Classification: hardware is physical, software is programs; system software (OS, utilities) vs application software; firmware is stored in ROM.

CPU components: ALU performs arithmetic/logic, control unit fetches and decodes instructions, registers hold operands; the machine cycle is fetch-decode-execute-store.

Clock speed is measured in GHz; more cores allow parallel execution but do not multiply single-thread speed.

RAM is volatile read/write memory; ROM is non-volatile. SRAM (cache) is faster and needs no refresh; DRAM needs periodic refresh.

Cache levels: L1 smallest and fastest, inside the core; L2 and L3 larger and slower; cache reduces average memory access time.

Motherboard holds CPU socket, RAM slots, chipset, BIOS/UEFI chip, expansion slots (PCIe) and I/O ports; the chipset links CPU to peripherals.

Storage: HDD uses rotating magnetic platters (RPM affects speed); SSD uses flash memory, has no moving parts, is faster and shock-resistant.

Ports: USB is hot-swappable and supplies power; HDMI carries digital video and audio; VGA is analog video only; RJ-45 is for Ethernet LAN.

Input devices: keyboard, mouse, scanner, microphone, webcam; output devices: monitor, printer, speaker, projector; a touchscreen is both.

Printers: inkjet sprays ink droplets; laser uses a drum, toner and fuser; dot matrix is impact and can print carbon copies.

OS functions: process management, memory management, file system management, device (I/O) management, security and user interface.

A process is a program in execution; the OS scheduler allocates CPU time; multitasking switches between processes rapidly.

Virtual memory uses part of secondary storage as an extension of RAM; thrashing is excessive paging that slows the system.

File systems: FAT32 has a 4 GB single-file limit, NTFS supports permissions and journaling, ext4 is common on Linux.

GUI vs CLI: GUI uses windows, icons and pointer; CLI accepts typed commands (cmd, PowerShell, Bash) and enables scripting.

Utility software: antivirus, disk defragmenter, disk cleanup, compression tools, backup tools, file managers and task managers.

Windows tools: Task Manager shows processes and CPU/RAM use; Device Manager shows hardware and driver status; msconfig controls startup items.

Linux basics: everything is a file; commands include ls, cd, cp, mv, rm, chmod; root has full privileges; sudo elevates rights.

A device driver is software that lets the OS communicate with a specific hardware device; a wrong driver causes device malfunction.

Assembly order: install CPU and cooler, then RAM, then mount the motherboard in the case, then PSU, drives, and finally cables and expansion cards.

CPU alignment: match the triangle or notch marker on the CPU with the socket corner; never force the lever; apply a thin, even layer of thermal paste.

RAM must match the slot type (DDR generation) and is keyed by a notch; dual-channel requires matched pairs in the correct slots.

Power connectors: 24-pin ATX for the motherboard, 4/8-pin EPS for CPU, 6/8-pin PCIe for graphics cards, SATA power for drives.

Anti-static precautions: use a wrist strap or touch grounded metal, work on a hard surface, avoid carpets, hold cards by the edges.

BIOS/UEFI setup configures boot order, date/time, virtualization, SATA mode and fan control; save and exit to apply changes.

OS installation: boot from installation media, partition and format the disk, complete setup, then install chipset, network and graphics drivers.

POST beeps or codes indicate hardware faults at startup; a single short beep usually means POST passed.

After assembly, verify in BIOS that CPU, RAM capacity and drives are all detected before installing the OS.

Preventive maintenance schedule: clean dust from fans, vents and heatsinks, check cables, update antivirus definitions and verify backups.

Compressed air is used in short bursts with the fan held still; avoid touching components with the nozzle or using a vacuum that creates static.

Troubleshooting sequence: identify the problem, establish a theory, test the theory, plan and implement a fix, verify function, document.

No power: check power cable, PSU switch, wall outlet and PSU tester before suspecting the motherboard.

No display: check monitor power and input source, reseat RAM and graphics card, test with another cable or monitor.

Overheating causes random shutdowns; check fan operation, dust blockage and thermal paste; monitor temperatures in BIOS or software.

Beep codes and POST cards localize faults; repeated beeps often indicate RAM or graphics failure; no beep with no display suggests power or CPU.

Hard disk errors: run check disk or SMART tests; clicking noises from an HDD indicate mechanical failure and data should be backed up first.

Document each repair: symptom, diagnosis, action taken and parts replaced, so recurring faults can be traced.

OSI has 7 layers (Physical, Data Link, Network, Transport, Session, Presentation, Application); TCP/IP model has 4 layers.

IPv4 is 32-bit dotted decimal (e.g., 192.168.1.10); IPv6 is 128-bit hexadecimal; private ranges are 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16.

Subnet mask separates network and host bits; /24 = 255.255.255.0; the default gateway is the router address used to reach other networks.

DNS resolves domain names to IP addresses; DHCP automatically assigns IP address, mask, gateway and DNS to clients.

TCP is connection-oriented and reliable (used by HTTP, FTP, email); UDP is connectionless and faster (used by streaming and DNS queries).

Common ports: HTTP 80, HTTPS 443, FTP 21, SSH 22, SMTP 25, DNS 53, DHCP 67/68, Telnet 23.

LAN vs WAN: LAN covers a limited area and is usually owned by one organization; WAN spans large distances, and the Internet is the largest WAN.

Devices: hub broadcasts to all ports, switch forwards by MAC address, router forwards by IP address, modem converts signals for the ISP line.

Wi-Fi security: WPA2/WPA3 preferred over WEP; change default router admin password and SSID; MAC filtering is a weak control.

CIA triad: confidentiality (authorized access only), integrity (data unaltered), availability (accessible when needed).

Malware types: virus attaches to files, worm spreads by itself over networks, Trojan disguises as useful software, ransomware encrypts data for payment.

Backup types: full copies all data; incremental copies changes since the last backup of any type; differential copies changes since the last full backup.

3-2-1 rule: keep 3 copies of data, on 2 different media, with 1 copy offsite or offline.

Restore testing is required: an untested backup cannot be assumed recoverable.

Strong password practice: long length, mixed character types, no dictionary words, unique per account, stored in a password manager.

Phishing defense: verify sender address, avoid links in unexpected mail, never share OTPs or passwords; report suspicious messages.

Antivirus must be updated regularly and a full scan scheduled; quarantine isolates suspected files instead of deleting immediately.

Encryption protects data at rest and in transit (HTTPS/TLS); access control uses authentication plus permissions (least privilege).

Word processing: Ctrl+C copy, Ctrl+X cut, Ctrl+V paste, Ctrl+Z undo, Ctrl+Y redo, Ctrl+S save, Ctrl+P print, Ctrl+F find.

Formatting vs content: styles apply consistent headings and enable automatic table of contents; page setup controls margins, orientation and size.

Spreadsheet cell references: relative (A1) changes when copied; absolute ($A$1) stays fixed; mixed ($A1 or A$1) fixes row or column only.

Common spreadsheet functions: SUM, AVERAGE, COUNT, COUNTA, MAX, MIN, IF, VLOOKUP; a formula always begins with =.

Charts: column for comparison, line for trends over time, pie for proportions of a whole; label axes and units.

Presentation rules: one idea per slide, readable font size, high contrast, limited bullet count, consistent theme, avoid clutter.

Mail merge combines a main document with a data source to produce personalized letters, labels or envelopes.

File formats: .docx, .xlsx, .pptx are editable; PDF preserves layout across systems; CSV stores plain comma-separated tabular data.

Print layout checks: print preview, page count, headers/footers, spell check and grammar check before final output.

E-waste includes discarded computers, monitors, printers, batteries and cables; it contains lead, mercury, cadmium and brominated flame retardants.

E-waste must go to authorized recyclers or take-back schemes; it must never be mixed with ordinary municipal waste or burned in the open.

CRT monitors and old batteries are hazardous: handle carefully, avoid breakage, and store in labeled containers before collection.

Data security at disposal: wipe or physically destroy storage media before recycling or resale to prevent data leakage.

Electrical safety: power off and unplug before opening a case, avoid wet hands, do not overload sockets, use properly rated UPS and surge protectors.

Ergonomics: monitor top at or slightly below eye level, elbows near 90 degrees, feet flat, short breaks to reduce eye strain and RSI.

Fire safety: electrical fires need CO2 or dry powder extinguishers, never water; know the location of exits and the assembly point.

Workplace practice: follow lab rules, keep aisles clear, label cables, report faults, use PPE where required, and record incidents.

Resource conservation: enable power-saving modes, reuse components where safe, print only when needed, and prefer duplex printing.