Block 2 Study Guide

Power on → POST → bootstrap loader → OS

Pressing the power button wakes the power supply, which checks its own output voltage then signals the CPU over the "power good" wire. The CPU immediately jumps to a built-in address holding the POST (Power-On Self-Test) program in motherboard ROM. POST has every device run its own diagnostic and report back — failures show as beep codes (one long + two/three short = bad video; one repeating beep = bad/missing RAM) or on-screen text errors.

After POST, control passes to the bootstrap loader in BIOS, which reads CMOS settings to know which storage device to check first for a bootable OS (a device with a valid boot sector). If no bootable device is found anywhere in the CMOS boot order, you get "boot device not found."

BIOS is non-volatile firmware permanently stored on motherboard ROM that provides "basic life support" to initialize hardware at startup — now considered legacy. UEFI (Unified Extensible Firmware Interface) replaced it starting in 2007 and is standard on nearly everything made since 2014, adding better bootstrapping, network booting, disk partitioning, hardware security, a modern GUI, and cryptography — while still supporting legacy BIOS compatibility. Many technicians still call both of them "BIOS" out of habit.

RAM is volatile "main memory" where the CPU actively works (unlike non-volatile storage, which holds data long-term). DRAM (Dynamic RAM) stores each bit as a charge in a capacitor that leaks and must be refreshed thousands of times a second — cheap but comparatively slow. SRAM (Static RAM) stores each bit in a flip-flop circuit that never needs refreshing — much faster, but more expensive and lower density, which is why it's used for CPU cache while DRAM forms the bulk of system memory.

Memory ships on sticks: SIMM/DIMM (desktop), SO-DIMM (laptops/small form factor). DDR (Double Data Rate) SDRAM transfers on both the rising and falling clock edge; each generation (DDR2 → DDR5) roughly doubles speed, with DDR5 also adding on-chip error correction and per-module power management. ECC RAM can detect and correct errors on the fly but is rarely used today. CMOS RAM (a type of SRAM) remembers hardware settings using a small battery; VRAM lives on the graphics card and determines resolution/color depth.

A major memory failure locks up the system, typically via a Non-Maskable Interrupt (NMI, an interrupt the CPU can't ignore) or a General Protection Fault (GPF — often two applications fighting over the same memory block). Both can produce a Blue Screen of Death (BSOD). Clock speed is the fastest rate a CPU can operate, generated by a quartz oscillator — from 4.77MHz on the 1979 Intel 8088 to 5GHz+ on modern CPUs, sometimes pushed further via overclocking.

Quick summary: the motherboard's chipset is split into Northbridge (fast interface between CPU, RAM, and video — often integrated into the CPU on modern systems) and Southbridge (slower devices like USB and disk controllers; called the I/O Controller Hub on Intel, Fusion Controller Hub on AMD). ROM stores small permanent programs called services (now usually flash memory, updatable by "flashing"). CMOS is the battery-backed menu of user hardware settings — commonly confused with BIOS, but BIOS is the code, CMOS is the settings menu it exposes.

A bus is a data pathway. The system bus connects major components and is made of three parts: the address bus (which memory location to access), the control bus (status signals, e.g. is the CPU reading or writing), and the data bus (the actual bidirectional data). The internal/local bus connects components to the motherboard itself; the external bus reaches outward to peripherals; the expansion bus connects to expansion slots like PCIe.

Three main internal structures: the Control Unit (directs the CPU, provides timing/control signals to memory, ALU, and I/O), the ALU (Arithmetic Logic Unit — performs math/logic operations on binary integers), and Registers (small, extremely fast holding places for an instruction, address, or data — sized to match the CPU's word length, e.g. 64 bits).

CPU cache is a 3-level hierarchy (L1/L2/L3) of SRAM sitting in or next to the CPU, storing frequently-used data to avoid slower round-trips to main RAM. PGA (Pin Grid Array) CPUs have pins on the chip itself, easily bent during installation; LGA (Land Grid Array, standard since 2004) flips this — flat contacts on the chip, pins built into the motherboard socket — making installation safer.

Quick summary: storage (secondary memory) is non-volatile, unlike RAM. It falls into three categories — magnetic (HDD, tape), optical (CD/DVD/Blu-ray), and solid-state (SSD, flash/thumb drives, SD cards). Flash memory is non-volatile, silent, has no moving parts, and is ideal for battery-powered devices — but costs more per GB than HDD and wears out after a finite number of write cycles.

A video card contains a GPU (a dedicated microprocessor that offloads graphics work from the CPU), its own VRAM, a video BIOS, and a RAMDAC (converts the GPU's digital signal into analog for older displays).

A NIC connects a computer to a network — built into the motherboard or a separate expansion card, wired (RJ-45 Ethernet port to a switch) or wireless (small antenna to an AP). Every NIC has a unique 48-bit hex MAC address burned in at manufacture; no two NICs on the same network can share one. A NIC operates at both OSI Layer 1 (physical access to the medium) and Layer 2 (MAC addressing).

Pressing a key generates a unique scan code, stored in a register and passed to the keyboard controller — handled by BIOS code, not the OS, which is why a keyboard works before an OS even loads. The keyboard is the primary human interface; the mouse is an alternate cursor-control device.

Every I/O device gets a unique I/O port address (like a street address, so the processor knows who it's talking to) and can raise an IRQ (Interrupt Request) to tell the CPU "pause and handle me" — a sound card finishing playback or a printer finishing a job, for example. An interrupt controller prioritizes incoming IRQs before forwarding them to the CPU. Device drivers are the software that lets the OS talk to hardware; installing the wrong driver (or an unsigned one not on the Hardware Compatibility List) can cause malfunctions.

The USB host controller (built into the chipset) manages every connected device through a root hub, which can theoretically support up to 127 devices — though piling that many onto one bus in practice slows everything down and strains DC power delivery. USB devices fall into 21 classes by function, e.g. HID (Human Interface Device — keyboards, mice, controllers) and Mass Storage Class (flash drives, external HDDs). USB Power Delivery (USB PD) now supports 5V/9V/12V/20V, up to 5A and 100W — enough to charge a laptop.

A sound card inputs/outputs audio for music, video editing, presentations, and games — often integrated into the motherboard rather than a separate expansion card. A line-in jack accepts analog audio sources; a separate microphone jack accepts the lower-voltage signal typical of mics, commonly used for speech recognition or VoIP.

A PSU converts AC wall power (100/120V or 220/240V) into low-voltage DC for internal components, following the ATX form factor for interchangeability. ATX supplies output +3.3V, +5V, -5V, +12V, and -12V "rails" (color-coded: black=ground, orange=+3.3V, red=+5V, yellow=+12V) and turn on/off via a motherboard signal. Common connectors: the large 20/24-pin motherboard connector, 4-pin Molex (drives), "P4" 4-pin auxiliary (CPU power), SATA power, and 6/8-pin PCIe (graphics cards).

Heat sinks (aluminum, copper, or brass fins) dissipate CPU/GPU heat by radiation and convection; thermal paste fills microscopic gaps between the chip and heat sink for much better conduction than air alone. Modern systems add active cooling — CPU fans, case fans (front-intake/rear-exhaust patterns), and for high-end builds, liquid cooling (a heat exchanger on the CPU, pumped coolant, and a radiator with its own fans) for far more effective heat transfer than air.

System software (the OS and utilities managing hardware at a low level) underlies application software (the programs that do real user-facing work). COTS (Commercial Off-The-Shelf) software like Microsoft Office is ready-made and purchased, not custom-built.

Copyright grants exclusive rights to publish/sell/distribute a work. A license agreement only grants the right to use software under specific terms — the publisher retains ownership. An Enterprise License covers many copies under one organization-wide agreement (often more cost-effective than individual licenses); an Enterprise Software Agreement (ESA) is the contract vehicle for acquiring it.

Before software can run on an Air Force network, it must appear on the DoDIN Approved Product List (APL) — a 13–15 month certification process managed by DISA's Approved Products Certification Office (APCO), covering both Cybersecurity/IA testing (STIG-compliant configuration) and Interoperability testing.