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  • Converting Number Systems

    IPv4 addresses 232=4,294,967,2962^{32}=4,294,967,296

    n 27262524232221202^7 2^6 2^5 2^4 2^3 2^2 2^1 2^0

    Assignable IP addresses 2h−22^h-2

    Subnets 2s2^s

    block size 256−InterestingOctet256-Interesting Octet

    1. 2748÷16=1712748 \div 16 = 171 with a remainder of 1212; the hexadecimal value for 1212 is CC.
    2. 171÷16=10171 \div 16=10 with a remainder of 1111; the hexadecimal value for 1111 is BB.
    3. 10÷16=010 \div 16=0 with a remainder of 10; the hexadecimal value for 1010 is AA.
    4. The decimal value 27482748 in hexadecimal format is ABCABC.

    248÷2=124 124÷2=62124÷2=62124÷2=62

    \begin{equation} \begin{split} 124÷2 =62\\ 124÷2=62\\ 62÷2=31\\ 31÷2=15\\ 15÷2=7\\ 7÷2=3\\ 3÷2=1\\ 1÷2=0 \end{split} \end{equation}

    1: 124÷2=62124÷2=6262÷2=3131÷2=1515÷2=77÷2=33÷2=11÷2=0124÷2 =62\\ 124÷2=62\\ 62÷2=31\\ 31÷2=15\\ 15÷2=7\\ 7÷2=3\\ 3÷2=1\\ 1÷2=0

    124÷2=62124÷2=6262÷2=3131÷2=1515÷2=77÷2=33÷2=11÷2=0\begin{equation} \begin{split} 124÷2 =62\\ 124÷2=62\\ 62÷2=31\\ 31÷2=15\\ 15÷2=7\\ 7÷2=3\\ 3÷2=1\\ 1÷2=0 \end{split} \end{equation}
    • 248÷2=124248÷2=124
    • 124÷2=62124÷2=62
    • 62÷2=3162÷2=31
    • 31÷2=1531÷2=15
    • 15÷2=715÷2=7
    • 7÷2=37÷2=3
    • 3÷2=13÷2=1
    • 1÷2=01÷2=0
    3ax+4by=5cz3ax<4by+5cz\begin{align*} 3ax+4by=5cz\\ 3ax<4by+5cz\\ \end{align*}

    Total IPv6 2128=3.4x10382^{128}=3.4×10^{38}

    A=πr22=12πr2\begin{equation} \label{eq1} \begin{split} A & = \frac{\pi r^2}{2} \\ & = \frac{1}{2} \pi r^2 \end{split} \end{equation}

    slope-intercept form: y=mx+by=mx+b ;

    standard quadratic form: ax2+bx+c=0ax^2+bx+c=0 ; quadratic forumal: x=−b±b2−4ac2ax=\frac{-b \pm \sqrt{b^2-4ac}}{2a}

    speed: S=rtS=rt; distance: time:

    Spacesinmathematicalmode.f(x)=x2+3x+2f(x)=x2+3x+2f(x)=x2+3x+2f(x)=x2+3x+2f(x)=x2+3x+2f(x)=x2 +3x +2f(x)=x2+3x+2f(x)=x2+3x+2Spaces in mathematical mode. \begin{align*} f(x) &= x^2\! +3x\! +2 \\ f(x) &= x^2+3x+2 \\ f(x) &= x^2\, +3x\, +2 \\ f(x) &= x^2\: +3x\: +2 \\ f(x) &= x^2\; +3x\; +2 \\ f(x) &= x^2\ +3x\ +2 \\ f(x) &= x^2\quad +3x\quad +2 \\ f(x) &= x^2\qquad +3x\qquad +2 \end{align*}

    i\hbar\frac{\partial}{\partial t}\left|\Psi(t)\right>=H\left|\Psi(t)\right>

    iℏ∂∂t|Ψ(t)⟩=H|Ψ(t)⟩i\hbar\frac{\partial}{\partial t}\left|\Psi(t)\right>=H\left|\Psi(t)\right>

  • IP Addressing & Subnetting — Complete Guide

    IP addressing is the foundation of all networking. Every device on a network must have a unique IP address, and subnetting determines how networks are divided, how many hosts they support, and how routing behaves.

    This guide covers IPv4, IPv6, subnet masks, CIDR notation, calculating network ranges, and converting between number systems — all using the formulas already shown in your Number Systems page .

    IPv4 Addressing Basics

    An IPv4 address is 32 bits, producing:

    232=4,294,967,296 total addresses

    IPv4 is written in dotted‑decimal format:

    192.168.1.10

    Each octet is 8 bits.

    Subnet Masks & CIDR Notation

    A subnet mask defines how many bits belong to:

    • Network portion
    • Host portion

    Example:

    255.255.255.0 = /24

    Meaning:

    • 24 network bits
    • 8 host bits

    Calculating Assignable Hosts

    Assignable Hosts=2h−2

    Where:

    • h = number of host bits
    • Subtract 2 for network and broadcast addresses

    Example: /24

    • Host bits = 8
    • Assignable = 28−2=254

    Calculating Number of Subnets

    Formula:

    Subnets=2s

    Where:

    • s = number of borrowed bits (bits added to the default mask)

    Example: Borrow 3 bits → 23=8 subnets.

    Interesting Octet & Block Size

    Formula:

    Block Size=256−Interesting Octet

    The interesting octet is the octet where the subnet mask stops being 255.

    Example:

    Mask: 255.255.255.192
Interesting Octet = 192
Block Size = 256 - 192 = 64

    Subnets:

    0–63
64–127
128–191
192–255

    Calculating Network & Broadcast Addresses

    Given an IP and mask:

    Step 1 — Find block size

    Use the formula above.

    Step 2 — Determine which block the IP falls into

    Example:

    IP: 192.168.1.130
Mask: /26 (block size 64)

    Blocks:

    • 0–63
    • 64–127
    • 128–191 ← IP falls here
    • 192–255

    Step 3 — Network & Broadcast

    Network:   192.168.1.128
Broadcast: 192.168.1.191

    Step 4 — Usable Range

    192.168.1.129 – 192.168.1.190

    Binary, Hex, and Octal Conversions

    Your Number Systems page already includes the conversion examples:

    Decimal → Hexadecimal

    Example from your draft: 2748 → ABC (A=10, B=11, C=12)

    Decimal → Binary

    Repeated division by 2 (your draft shows the full breakdown)

    Binary → Hex

    Group bits into 4s.

    Binary → Octal

    Group bits into 3s.

    These conversions are essential for understanding subnetting at the bit level.

    IPv6 Addressing Basics

    Your draft includes the total IPv6 address space:

    2128=3.4×1038

    IPv6 uses:

    • 128‑bit addresses
    • Hexadecimal notation
    • No broadcast addresses
    • Vastly simplified subnetting

    Example:

    2001:db8:abcd:0012::/64

    CIDR Summary Table

    CIDRHostsBlock SizeNotes
    /242541Common LAN
    /25126128Split /24 in half
    /266264Cameras, IoT
    /273032Small networks
    /3024Point‑to‑point links

  • USB Specifications

    USB (Universal Serial Bus) is a standardized serial interface used to connect peripheral devices to a computer. It supports multiple device types, hot‑swapping, plug‑and‑play, and a wide range of speeds and connector formats.

    USB Versions & Speeds

    Your page lists the USB versions and speeds accurately, including USB 1.0 → USB4. Here is the cleaned and corrected table with modern naming:

    USB VersionMarketing NameMax SpeedCable LengthNotes
    USB 1.0 / 1.1Low‑Speed / Full‑Speed1.5 Mbps / 12 Mbps3–5 mLegacy
    USB 2.0High‑Speed480 Mbps5 mBackward‑compatible with 1.1
    USB 3.0 / 3.1 Gen 1SuperSpeed 5 Gbps5 Gbps~3 mBackward‑compatible with 2.0
    USB 3.1 Gen 2SuperSpeed+ 10 Gbps10 Gbps~3 m
    USB 3.2 Gen 1×2SuperSpeed 10 Gbps10 GbpsUSB‑C only
    USB 3.2 Gen 2×2SuperSpeed 20 Gbps20 GbpsUSB‑C only
    USB4 (v1)USB4 20/40 Gbps20–40 GbpsUSB‑C only
    USB4 (v2)USB4 80/120 Gbps80 Gbps symmetric / 120 Gbps asymmetricUSB‑C only

    You should know the following facts about USB:

    • USB is a serial interface that supports low- and high-speed devices. 
    • USB supports almost any kind of peripheral device, including keyboards, mice, scanners, digital cameras, printers, and storage devices.
    • USB supports Plug-and-Play and hot swapping (adding and removing devices without rebooting–also known as hot plugging).
    • USB allows 127 devices to be connected to a single computer (directly to the host or by hubs).
    • All devices connected together share computer resources (IRQs, I/O addresses).
    • The computer’s BIOS must support USB and have USB enabled.

    USB comes in multiple versions that perform at different rates, for various devices, as listed in the table below.

    VersionSpeedData Transfer Rate (megabits per second)Maximum Cable Length (meters)Supported connectors
    1.0/1.1Low-speed1.5 Mbps3 mUSB 3.0 Standard-A, USB 3.0 Standard-B, USB 3.0 Micro-B, USB 3.0 Micro-A, USB 3.0 Micro-AB, USB-C
    Full-speed12 Mbps5 m
    2.0High-speed480 Mbps5 m
    3.1 Gen 1×1 (3.0/3.1 Gen 1)Super-SpeedUp to 5 Gbps3 m
    3.2 Gen 2×1 (3.1 Gen 2)SuperSpeed USB 10GbpsUp to 10 Gbps 
    3.2 Gen 1×2 USB-C
    3.2 Gen 2×2SuperSpeed USB 20GbpsUp to 20 Gbps 
    4 20 Gbps / 40 Gbps 
    4 version 2 80 Gbps Symmetrically (Up to 120 Gbps asymmetrically) 

    ** Version 2.0 is backwards compatible with version 1.1 devices. Likewise, Version 3.0 is backwards compatible with version 2.0 devices. Most motherboards allow you to enable/disable USB support in the BIOS, or configure the USB version that will be used.

    ConnectorDescription
    USB Type‑A
    		Rectangular connector that generally plugs directly into the computer or a hub.
    USB Type‑B
    		Square/D‑shaped connector used for printers, hubs, and some peripherals.
    Mini‑USB (4 pin)Small square connector designed to plug in to devices with mini plugs such as a digital camera. Most USB cables with a mini connector have an A connector on the other end to connect to the computer
    Mini‑USB (5 pin)Small connector designed to plug in to devices with mini plugs such as a digital camera.
    Micro‑USBMicro USB connectors are designed for smart phones and tablet devices. As such, micro USB connectors are quickly replacing mini USB connectors. Micro USB connectors are approximately half the thickness of Mini USB connectors, making them more appropriate for smaller devices.
    USB‑CReversible connector supporting USB 3.x, USB4, Thunderbolt 3/4, DisplayPort Alt Mode, and power delivery.

    You can connect a USB device to a computer in two ways:

    • Directly to a USB port on a computer (it is common for a computer to have two USB ports). In addition, many motherboards include additional USB headers that can be used to attach additional USB ports.
    • To an external USB hub. Hubs can be chained together to provide additional ports. A hub has a single B connector to connect to the computer, and multiple A connectors for attaching devices.

    USB devices can be classified according to how they receive power.

    Device TypeDescription
    Self-poweredDevices that rely on their own power supply (in other words, you plug them into an AC outlet) are self-powered devices (sometimes called active devices). All devices that draw more than 500 mA of power are required to be self-powered.
    Bus poweredUSB cables have wires to carry both power and data. Bus-powered (sometimes called passive) devices get their power from the USB cable. Bus-powered devices are classified as low-powered or high-powered devices depending on the amount of power they draw from the USB bus. Low powered devices use 100 mA or less High-powered devices use between 100 and 500 mA Like USB devices, USB hubs can be bus-powered or self-powered. You cannot connect high-powered devices to a bus-powered hub (you can only connect low-powered or self-powered devices to a bus-powered hub). Therefore, self-powered hubs that provide 500 mA per port are recommended to ensure an adequate power supply to all bus-powered devices that you may wish to connect to the hub.

    ** To install a USB device, you typically install the software driver before attaching the device. When you plug in the device, it will be automatically detected and configured.

    USB Power Types

    Self‑Powered Devices

    Devices with their own AC power supply. Required for devices drawing more than 500 mA.

    Bus‑Powered Devices

    Devices powered directly from the USB port. Current page

    • Low‑power: ≤100 mA
    • High‑power: 100–500 mA

    USB Hubs

    • Can be bus‑powered or self‑powered
    • High‑power devices cannot be connected to bus‑powered hubs Current page
    • Self‑powered hubs recommended for reliability

    USB Installation & Detection

    Your page correctly states:

    • Install drivers before plugging in the device
    • Device is auto‑detected when connected Current page

    This is still true for many legacy devices, though modern OSes often include built‑in drivers.

  • SD Card – Speed and Specs

    A complete reference for SD card types, speed classes, bus interfaces, and performance ratings.

    Secure Digital (SD) cards are widely used in cameras, phones, embedded systems, and portable electronics. Their performance depends on three major factors:

    • Capacity class (SD / SDHC / SDXC / SDUC)
    • Speed class (C, U, V, E)
    • Bus interface (Standard, High‑Speed, UHS‑I/II/III, Express)

    This guide explains each classification and how to choose the right card for your device.

    Size

    SD, miniSD, microSD

    Storage Capacity Classes SD Card Capacity Classes

    TypeCapacity Range
    SD (Secure Digital)Up to 2 GB
    SDHC (High Capacity)>2 GB to 32 GB
    SDXC (Extended Capacity)>32 GB to 2 TB
    SDUC (Ultra Capacity)>2 TB to 128 TB

    Compatibility rule:

    • Devices that support SDXC also support SDHC and SD.
    • Devices that support SDUC support all previous types.
    • Older devices may NOT support SDXC or SDUC.

    Write speed ratings

    Bus Speed Ratings (Data Transfer Speeds)

    Bus TypeMax SpeedNotes
    Default Speed12.5 MB/sLegacy
    High‑Speed25 MB/sWidely supported
    UHS‑I50 MB/s or 104 MB/sSingle‑row contacts
    UHS‑II156 MB/s (full‑duplex) / 312 MB/s (half‑duplex)Second row of pins
    UHS‑III312 MB/s (full‑duplex) / 624 MB/s (half‑duplex)Rare
    SD Express985 MB/s+PCIe/NVMe‑based

    Important: Bus speed ≠ real‑world write speed. Bus speed is the maximum interface capability, not guaranteed performance.

    Speed Class Ratings (C, U, V, E)

    Original Speed Class (C)

    ClassMinimum Write Speed
    C22 MB/s
    C44 MB/s
    C66 MB/s
    C1010 MB/s
    Original Speed Class (C)

    UHS Speed Class (U)

    ClassMinimum Write Speed
    U110 MB/s
    U330 MB/s
    UHS Speed Class (U)

    Video Speed Class (V)

    ClassMinimum Write Speed
    V66 MB/s
    V1010 MB/s
    V3030 MB/s
    V6060 MB/s
    V9090 MB/s
    Video Speed Class (V)

    Express Speed Class (E)

    ClassMinimum Write Speed
    E150150 MB/s
    E300300 MB/s
    E450450 MB/s
    E600600 MB/s
    Express Speed Class (E)

    These are used for high‑end cameras, 4K/8K video, and SD Express devices.

    Application Performance Class rating

    Designates the minimum number of Input/Output Operations per Second (IOPS)

    ClassRead IOPSWrite IOPS
    A11,500500
    A24,0002,000

    These ratings matter for:

    • Smartphones
    • Tablets
    • Single‑board computers (Raspberry Pi)
    • App storage and random access workloads

    A2 cards require host support to reach full performance.

    Read speed rating

    The read speed rating of an SD card is usually indicated by the number and data unit, i.e. MB/s, that is printed on the front of the card (e.g., “100 MB/s”).

    Important:

    • Read speed is usually higher than write speed.
    • Manufacturers advertise read speed because it looks better.
    • Write speed is what matters for video recording.

    Choosing the Right SD Card

    For photography

    • U3 / V30 minimum
    • UHS‑I or UHS‑II depending on camera

    For 4K video

    • V30 or V60
    • Avoid C10/U1 cards

    For 8K video

    • V60 or V90
    • Prefer UHS‑II or SD Express

    For smartphones / app storage

    • A2 recommended

    For Raspberry Pi

    • A1 or A2
    • Avoid cheap unbranded cards

  • Wi-Fi Standards

    A complete reference for Wi‑Fi standards, frequencies, channels, security, antennas, and troubleshooting.

    Wireless networking is built on the IEEE 802.11 family of standards. Each generation improves speed, efficiency, and spectrum usage. This toolkit provides a technician‑grade reference for Wi‑Fi technologies, frequency bands, channel planning, security, and performance optimization.

    Wi‑Fi is defined by the IEEE 802.11 family of wireless networking standards. Each generation improves speed, range, efficiency, and spectrum usage. This guide summarizes every major Wi‑Fi standard from 802.11a to Wi‑Fi 7 and provides a technician‑grade reference for Wi‑Fi technologies, frequency bands, channel planning, security, and performance optimization.

    Wi‑Fi Standards Overview (802.11a → Wi‑Fi 7)

    SpecificationStandard
    802.11a802.11b802.11g802.11n (Wi‑Fi 4)802.11ac (Wi‑Fi 5)802.11ax (Wi‑Fi 6)802.11be (Wi‑Fi 7)
    Frequency5.75 GHz (U-NII)2.4  GHz (ISM)2.4 GHz (ISM)2.4 GHz (ISM) or 5 GHz (U-NII)5 GHz (optionally 2.4 GHz for compatibility)2.4, 5, 6 GHz (Wi‑Fi 6E adds 6 GHz)2.4/5/6 GHz
    Maximum speed54 Mbps11 Mbps54 Mbps150, 300, or 600 Mbps (MIMO)693 Mbps, 1.6 Gbps, 3.5 Gbps, 6.9 Gbpsup to 9.6 Gbpsup to 46.1 Gbps
    Maximum range150 Ft.300 Ft.300 Ft.1200 Ft.
    Modulation typeMU‑MIMO, 256‑QAMOFDMA (massive efficiency boost),
    1024‑QAM, Target Wake Time (TWT)
    Channels
    (non-overlapped)    		23 total, 12 non‑overlapping11 total, 3 non‑overlapping11 total, 3 non‑overlapping5 GHz → 23 total (12 or 6 non‑overlapping),
    2.4 GHz → 11 total (3 or 1 non‑overlapping)
    Channel widths80/160 MHz320 MHz
    Backwards-compatibilityN/ANo802.11b802.11a/b/g (depends on frequencies supported)
    NotesFirst 5 GHz Wi‑Fi standard; less interference but shorter range.Cheap, long‑range, but slow and interference‑prone.Introduced MIMO, channel bonding (40 MHz), and dual‑band Wi‑Fi.Major speed boost; dominant standard for years.Designed for dense environments (apartments, stadiums).Extremely high throughput; next‑generation wireless.
    Wi‑Fi Standards
     FrequencyMax SpeedMax RangeChannels (non-overlapping)Backwards-compatibility
    802.11a5.725 GHz – 5.850 (U-NII)54 Mbps150 Ft.  23 (12)N/A
    802.11b2.4 GHz (ISM)11 Mbps300 Ft.  11 (3)No
    802.11g2.4 GHz (ISM)54 Mbps300 Ft.  11 (3)With 802.11b
    802.11n2.4 GHz (ISM) or 5 GHz (U-NII)150, 300, or 600 Mbps1200 Ft.5.75 GHz–23 (12 or 6) 2.4 GHz–11 (3 or 1)With 802.11a/b/g, depending on frequencies supported
    802.11ac (Wi-Fi 5)2.4, 5693 Mbps, 1.6 Gbps, 3.5 Gbps, 6.9 Gbps  802.11a/b/g/n
    802.11ax (Wi-Fi 6)2.4, 5, 61.15, 2.3, 4.8, 9.6 Gbps   
    802.11be (Wi-Fi 7)2.4, 5, 611.5, 23, 35, 46.1 Gbps   
    StandardWi‑Fi NameFrequencyMax SpeedChannel WidthsKey Features
    802.11a (1999)—5 GHz54 Mbps20 MHzOFDM, low interference
    802.11b (1999)—2.4 GHz11 Mbps20 MHzDSSS, long range
    802.11g (2003)—2.4 GHz54 Mbps20 MHzOFDM, backward‑compatible
    802.11n (2009)Wi‑Fi 42.4/5 GHz150–600 Mbps20/40 MHzMIMO, channel bonding
    802.11ac (2013)Wi‑Fi 55 GHz693 Mbps–6.9 Gbps20/40/80/160 MHzMU‑MIMO, 256‑QAM
    802.11ax (2019–2021)Wi‑Fi 6/6E2.4/5/6 GHzUp to 9.6 Gbps20–160 MHzOFDMA, 1024‑QAM, TWT
    802.11be (2024+)Wi‑Fi 72.4/5/6 GHzUp to 46.1 Gbps20–320 MHzMLO, 4096‑QAM
    Wi‑Fi Standards

    Wi‑Fi Frequency Bands

    2.4 GHz

    • Longest range
    • Lowest throughput
    • Most interference (Bluetooth, microwaves, IoT)
    • Only 3 non‑overlapping channels (1, 6, 11)

    5 GHz

    • Medium range
    • High throughput
    • Many channels (DFS and non‑DFS)
    • Supports 20/40/80/160 MHz

    6 GHz (Wi‑Fi 6E / Wi‑Fi 7)

    • Shortest range
    • Extremely high throughput
    • Clean spectrum
    • Up to 59 channels depending on region
    • Supports 160/320 MHz channels

    Channel Widths & Channel Planning

    Channel Widths

    • 20 MHz — stable, best for crowded areas
    • 40 MHz — faster, but more interference
    • 80 MHz — high throughput (Wi‑Fi 5+)
    • 160 MHz — very high throughput (Wi‑Fi 6/7)
    • 320 MHz — Wi‑Fi 7 only

    Channel Planning Tips

    • Use 1/6/11 on 2.4 GHz
    • Avoid DFS channels if you want maximum compatibility
    • Use 80 MHz only when the spectrum is clean
    • Use 6 GHz for high‑density, high‑speed environments

    Wi‑Fi Security Standards

    StandardStatusNotes
    WEPObsoleteBroken encryption
    WPALegacyTKIP, insecure
    WPA2CurrentAES‑CCMP, widely used
    WPA3ModernSAE handshake, stronger protection

    Recommended: Use WPA3‑Personal or WPA2/WPA3 mixed mode for compatibility.

    Antennas, MIMO, MU‑MIMO, OFDMA, Beamforming

    MIMO (Multiple‑Input Multiple‑Output)

    • Multiple antennas increase throughput
    • Introduced in 802.11n

    MU‑MIMO (Multi‑User MIMO)

    • Router can talk to multiple clients simultaneously
    • Introduced in 802.11ac

    OFDMA (Orthogonal Frequency Division Multiple Access)

    • Splits channels into subcarriers
    • Great for dense environments
    • Introduced in 802.11ax

    Beamforming

    • Directs signal toward the client
    • Improves range and stability

    Wi‑Fi Device Types

    • Router — gateway + Wi‑Fi + switch
    • Access Point (AP) — dedicated wireless endpoint
    • Mesh System — multi‑node coverage
    • Range Extender — repeats signal (not recommended)
    • Wireless Bridge — connects wired devices to Wi‑Fi
    • Client Adapter — USB/PCIe Wi‑Fi card

    Wireless Site Survey Basics

    Key Metrics

    • RSSI (signal strength)
    • SNR (signal‑to‑noise ratio)
    • Channel overlap
    • Interference sources

    Placement Rules

    • Place APs high and central
    • Avoid metal, concrete, and appliances
    • Use wired backhaul for mesh systems

    Troubleshooting Quick Reference

    • Check signal strength
    • Switch to 5 GHz or 6 GHz
    • Change channels
    • Update firmware
    • Reposition AP
    • Reduce channel width
    • Check for interference
    • Restart DHCP or router

  • Electronic Color Codes

    Electronic components often use color bands or printed codes to indicate their electrical values. The most common example is the resistor color code, which uses colored stripes to show resistance, tolerance, and sometimes temperature coefficient. Older capacitors also used color codes, but modern capacitors now use printed numeric markings instead.

    This guide explains how to read both resistor and capacitor color codes accurately.

    Resistor Color Codes

    ColorDigitMultiplierToleranceTemp. Coefficient (ppm/K)
     Black0×1–250
     Brown1×10±1%100
     Red2×100±2%50
     Orange3×1,000–15
     Yellow4×10,000–25
     Green5×100,000±0.5%
     Blue6×1,000,000±0.25%10
     Violet7×10,000,000±0.1%5
     Gray8–±0.05%
     White9––
     Gold–×0.1±5%
     Silver–×0.01±10%
    Color Digit & Multiplier Table

    Usage: Color codes vs printed values

    Resistors that use color‑banded:

    • Through‑hole, low‑power resistors from about 1/8 W up to 2 W
    • Common carbon film, metal film, and carbon composition resistors
    • Used on PCBs, prototyping boards, and legacy equipment

    Resistors that use printed values (no color bands):

    • Surface‑mount resistors (SMD) — use numeric codes like “103” (10 kΩ), “472” (4.7 kΩ)
    • Higher‑power wire‑wound resistors (5 W, 10 W, etc.) — often have the resistance and tolerance printed directly on the body
    • Precision network / array resistors — usually labeled or coded in text

    Resistor Band Rules

    Resistors typically use 4‑band, 5‑band, or 6‑band color coding.

    4‑Band Resistor

    1. Band 1: First digit
    2. Band 2: Second digit
    3. Band 3: Multiplier
    4. Band 4: Tolerance

    Example: Red (2) – Violet (7) – Orange (×1,000×1,000) – Gold (±5±5%) → 27,000Ω±527,000 Ω ±5%

    5‑Band Resistor

    Used for precision resistors.

    1. Band 1: First digit
    2. Band 2: Second digit
    3. Band 3: Third digit
    4. Band 4: Multiplier
    5. Band 5: Tolerance

    Example: Brown – Black – Black – Red – Brown → 100×100=10kΩ±1100 × 100 = 10 kΩ ±1%

    6‑Band Resistor

    Same as 5‑band, plus:

    1. Band 6: Temperature coefficient (ppm/K)

    Example: Blue (10 ppm/K) indicates high stability.

    Frequently Asked Questions

    How do I read resistor color bands?

    Use the color table.

    • First two (or three) bands = digits
    • Next band = multiplier
    • Last band = tolerance Multiply the digits by the multiplier to get the resistance value.

    What is the difference between 4‑band and 5‑band resistors?

    • 4‑band = general‑purpose resistors
    • 5‑band = precision resistors with an extra digit
    • 6‑band adds temperature coefficientperspectives of each artist.

    Do capacitors still use color codes?

    No. Color‑coded capacitors are obsolete. Modern capacitors use printed numeric codes (e.g., “104”=100,000pF=0.1µF“104” = 100,000 pF = 0.1 µF).

    What does the gold or silver band mean?

    • Gold: ±5%±5\% tolerance
    • Silver: ±10%±10\% tolerance

    How do I know which side to read from?

    • The tolerance band (gold/silver/brown/red) is usually spaced farther apart or placed at the right end.
    • Start reading from the opposite side.

  • Ethernet Standards (IEEE 802.3)

    Ethernet is the dominant LAN technology used worldwide. The IEEE 802.3 standard defines how Ethernet operates at the physical and data link layers, including signaling, cabling, speeds, and maximum distances. This guide summarizes the most common Ethernet standards from 10 Mbps to 100 Gbps.

    ClassificationStandardBandwidth/SpeedMediumMaximum cable length
    Thicknet10BASE510 MbpsCoaxial500 meters
    Thinnet10BASE210 MbpsCoaxial185 meters
    Standard Ethernet10BASE-T10 Mbps (half duplex)Twisted pair (Cat3, 4, or 5)100 meters
    20 Mbps (full duplex)
    10BaseFL10 Mbps (multimode cable)Fiber optic1,000 to 2,000 meters
    Fast Ethernet100BaseTX100 Mbps (half duplex) Twisted pair (Cat5 or higher) Uses 2 pairs of wires100 meters
    200 Mbps (full duplex)
    155 Mbps (Asynchronous Transfer Mode; ATM)
    100BaseFX100 Mbps (multimode cable)Fiber optic412 meters (half-duplex)
    2 kilometers (full duplex)
    Gigabit Ethernet1000BaseT1,000 Mbps (half duplex)
    2,000 Mbps (full duplex)    		Twisted pair (Cat5e, Cat6 or higher)100 meters
    1000BaseCX (short copper)Special copper (150 ohm)25 meters, used within wiring closets
    1000BaseSX (short)Fiber optic

    		220 to 550 meters depending on cable quality
    1000BaseLX (long)Multi-mode optical fiber550 meters
    Single-mode optical fiber10 kilometers
    10 Gigabit Ethernet10GBASE-T10 Gbps (full duplex only)Twisted pair (Cat 6a, or higher)100 meters
    10GBaseSRMulti-mode optical fiber26–400 m
    10GBaseSW300 meters
    10GBaseLRSingle-mode optical fiber10–25 km
    10GBaseLW10 kilometers
    10GBaseER40 kilometers
    10GBaseEW
    40 Gigabit Ethernet40GBASE-T40 GbpsTwisted pair (Cat 8)30 to 36 meters
    100 Gigabit Ethernet100GBASE-SR10100 GbpsMulti-mode optical fiber125 m
    100GBASE-LR4Single-mode optical fiber (SMF)10 km
    100GBASE-ER440 km
    Ethernet Standards IEEE 802.3 Table

    non‑IEEE Ethernet Standards

    ClassificationStandardBandwidth/SpeedMediumMaximum cable lengthNotes
    Fast Ethernet100BASE‑SX100 MbpsMMF300 mVendor‑driven extension)
    Gigabit Ethernet1000BASE‑LH1 Gbps (half-duplex), 2 Gbps (full-duplex)SMF10 km1000BASE‑LH is not an IEEE standard. It is a Cisco/industry term for “long haul” optics, typically 20–70 km depending on optics.
    1000BASE‑ZX70 kmVendor‑driven extension)
    10 Gigabit Ethernet10GBASE‑EW10 Gbps (full-duplex only)SMF40 kilometersWAN PHY variants (SONET/SDH framing)
    10GBASE‑LW10 kilometers
    10GBASE‑SWMMF300 meters
    non‑IEEE Ethernet Standards Table

    Frequently Asked Questions

    What does “BASE” mean in Ethernet names?

    “BASE” means baseband signaling, where the entire bandwidth is used for Ethernet only.

    Why do some standards (like ZX or LH) not appear in IEEE tables?

    Because they are vendor‑defined, not official IEEE 802.3 standards.

    What does the letter after “BASE” mean?

    It indicates the medium:

    • T = Copper twisted pair
    • T = Twisted pair
    • SX = Short‑range fiber
    • LX = Long‑range fiber
    • SR/LR/ER = Short/Long/Extended fiber

    What does the number before “BASE” mean?

    It indicates the speed:

    • 100G = 100 Gbps
    • 10 = 10 Mbps
    • 100 = 100 Mbps
    • 1000 = 1 Gbps
    • 10G = 10 Gbps
    • 40G = 40 Gbps

    What is the maximum distance for twisted‑pair Ethernet?

    Almost all twisted‑pair standards (10BASE‑T, 100BASE‑TX, 1000BASE‑T, 10GBASE‑T) are limited to 100 meters.

  • Surface Book Keyboard: unknown USB device (device descriptor request failed)

    Error

    Unknown USB device (device descriptor request failed).

    Description

    In Bluetooth & devices > Devices in the Settings interface, under the Input section, the device with the keyboard icon says, “unknown USB device (device descriptor request failed)”.

    Solution

    • Expand the panel for the keyboard device.
    • Click the Remove this device link.
    • The operating system will try to reinstall the device with the proper driver. Warning: This may take up to a minute.

  • OSI Model

    LayerProtocol data unit (PDU)FunctionCommon Protocols
    Host layers  7Application  Data  High-level protocols such as for resource sharing or remote file access, e.g. HTTP. DNS, HTTP, HTTPS, FTP, POP, IMAP, SMTP, SNMP
    6PresentationTranslation of data between a networking service and an application; including character encoding, data compression and encryption/decryptionMIME, SSL/TLS, XDR
    5SessionManaging communication sessions, i.e., continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes Named pipe, NetBIOS, SAP, PPTP, RTP, SOCKS, X.225, Domain Name Sytem, Remote Procedure Call, Network File System
    4TransportSegment, DatagramReliable transmission of data segments between points on a network, including segmentation, acknowledgement, and multiplexingTCP, UDP, SCTP, DCCP, SPX
    Media layers3NetworkPacketStructuring and managing a multi-node network, including addressing, routing and traffic controlIP (IPv4, IPv6), ICMP, IPsec, IGMP, IPX, IS-IS, AppleTalk, X.25, PLP, RIP
    2DatalinkFrameTransmission of data frames between two nodes connected by a physical layerATM, ARP, Synchronous Data Link Control, High-Level Data Link Control, CSLIP, Serial Line Interface Protocol, GFP, PLIP, IEEE 802.2, LLC, MAC, L2TP, IEEE 802.3, Frame Relay, ITU-T G.hn DLL, Point-to-Point Protocol, X.25 LAPB, Q.922 Link Access Procedure, STP
    1PhysicalBit, SymbolTransmission and reception of raw bit streams over a physical medium RS-232, RS-449, ITU-T V-Series, I.430, I.431, PDH, SONET/SDH, PON, OTN, DSL, IEEE 802.3, IEEE 802.11, IEEE 802.15, IEEE 802.16, IEEE 1394, ITU-T G.hn PHY, USB, Bluetooth
    OSI ModelProtocol data unit (PDU)Protocols
    LayerProtocol data unit (PDU)Protocols
    Layer 4Application SMTP, FTP, HTTP, DNS, TFTP, RIP, SNMP
    Layer 3TransportSegment, DatagramTCP, UDP
    Layer 2InternetPacketARP, RARP, IP, IGMP, ICMP
    Layer 1Link (Network Access/ Interface)FrameEthernet, 802.11 Wireless LAN, FRAME RELAY, ATM
    OSI ModelProtocol data unit (PDU)Protocols
    OSI ModelProtocol data unit (PDU)Protocols
    Layer 7ApplicationDataDNS, HTTP, HTTPS, FTP, POP, IMAP, SMTP, SNMP
    Layer 6PresentationDataMIME, SSL/TLS, XDR
    Layer 5SessionDataNamed pipe, NetBIOS, SAP, PPTP, RTP, SOCKS, X.225, Domain Name System, Remote Procedure Call, Network File System
    Layer 4TransportSegment, DatagramTCP, UDP, SCTP, DCCP, SPX
    Layer 3NetworkPacketIP (IPv4, IPv6), ICMP, IPsec, IGMP, IPX, IS-IS, AppleTalk, X.25, PLP, RIP
    Layer 2Data LinkFrameATM, ARP, Synchronous Data Link Control, High-Level Data Link Control, CSLIP, Serial Line Interface Protocol, GFP, PLIP, IEEE 802.2, LLC, MAC, L2TP, IEEE 802.3, Frame Relay, ITU-T G.hn DLL, Point-to-Point Protocol, X.25 LAPB, Q.922 Link Access Procedure, STP
    Layer 1PhysicalBit, SymbolRS-232, RS-449, ITU-T V-Series, I.430, I.431, PDH, SONET/SDH, PON, OTN, DSL, IEEE 802.3, IEEE 802.11, IEEE 802.15, IEEE 802.16, IEEE 1394, ITU-T G.hn PHY, USB, Bluetooth

  • Where Are iptables-persistent/iptables-services Rules Files Located in cPanel/WHM?

    Location of IPv4 file: /etc/sysconfig/iptables

    Location of IPv6 file: /etc/sysconfig/ip6tables

    Linux Command to Access Them Directly

    1. In the terminal,
    2. Type (or paste) vi /etc/sysconfig/ip6tables for IPv6 file, or
    3. vi /etc/sysconfig/iptables for IPv4 file

    Linux Command to Get to Directory

    1. In the terminal,
    2. Type (or paste) cd /etc/sysconfig to navigate to the sysconfig directory, or
    3. ls /etc/sysconfig to list items in the sysconfig directory.

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