CompTIA A+ Notes

Troubleshooting Theory Steps

1. Identify the problem

2. Establish a theory of probable cause

3. Test the theory to determine the cause

4. Establish a plan of action to resolve the problem and implement the solution

5. Verify full system functionality and, if applicable, implement preventative measures

6. Document findings, actions, and outcomes

PC form factors for closed case devices

1. Full tower (extended ATX or eATX)

2. Mid tower (ATX)

3. Mini tower (ATX, Micro-ATX, or mATX

4. Small form factor (SFF or mini-ATX)

Most common Instruction Set Architectures for CPUs

1. x86

   1. Is a Complex Instruction Set Computer (CISC)

   2. Has a focus on hardware

   3. 32-bit CPU

   4. Slower

2. x64

   1. Is a Reduced Instruction Set Computing (RISC) device

   2. Can handle 32 and 64 bit software

   3. Faster

3. Advanced Risk Machine (ARM)

   1. Based on x64 architecture

   2. Designed for efficiency and to use less power

CPUs are measured by:

1. Cores

   1. Multiple processors placed onto the same chip

   2. The more cores, the better the clock speeds

2. Clock speeds

   1. Measured by the number of tasks done in 1 second

   2. Clock cycles are the CPU’s speed, represented by the number of cycles per second

CPU motherboard sockets

1. Land Grid Array (LGA) - Intel motherboards

2. Pin Grid Array (PGA) - AMD motherboards

RAM Technologies

1. Synchronous Dynamic Random Access Memory (SDRAM)

   1. The “1st” ram (not actually, but the first mentioned)

   2. Synced to the same clock as the CPU

   3. 168 pins

2. Double Data Rate (DDR) SDRAM

   1. For every 1 clock click, gets 2 bits of information

   2. 184 pins

3. DDR2

   1. 240 pins

4. DDR3

   1. 240 pins

5. DDR4

   1. 288 pins

6. DDR5

   1. 288 pins

Each doubles the speed of its predecessor

Types of RAM

1. Double sided RAM

   1. Has RAM on both sides

2. Error Correction Code RAM

   1. The older version of this is Parity RAM

   2. RAM that has an extra 2 chips. If functioning chips go bad, these will replace them

3. Small Outline Dual Inline Memory Module (SO-DIMM)

   1. Used in small form devices, like laptops

BIOS

Basic Input/Output System

Bios is firmware, meaning it’s software stored/burned onto Read Only Memory chips found on your motherboard

Some systems have 2 BIOS chips, one M Main BIOS chip and a B Backup chip

BIOS checks that all hardware components in a system are present, active, and ready on device turn on (POST)

The original BIOS is called Legacy BIOS, and was very limited, leading to the creation of EFI or Extensible Firmware Interface

16 bit

UEFI and EFI

Extensible Firmware Interface was expanded into Unified Extensible Firmware Interface, providing support for larger storage devices, GPT partitioning, enhanced security, faster boot times, etc

UEFI has a GUI

64 bit

The CPU has instructions for loading and starting BIOS (and UEFI) from the firmware, not stopping until the OS is loaded into the RAM

UEFI stores the startup configuration in a data file with an EFI extension, being stored in a specialized EFI system partition which contains the bootloader for the OS

POST

Stands for Power-On Self Test

The CPU communicates with the PC’s hardware, telling them to check themselves and communicate back

If the hardware is good, the computer POSTS. If not, you’re receive beep codes or a displayed error code

System Setup

Where you make changes to the changeable parts of UEFI BIOS

To get to system setup, you hold the delete key or the F2 key while your PC is booting (generally)

Motherboard Form Factors

1. ATX

   1. Most common form factor: 12 by 9.6 in

2. Micro ATX

   1. 9.6 × 9.6 in

3. ITX

   1. Larger form factor over the mini ITX

4. Mini ITX

   1. Smallest form factor

Motherboard Cable Connections

1. ATX 24-pin connector

   1. Consists of 2 connectors

      1. 20-pin connector

      2. 4-pin connector

   2. Connects the motherboard to the PSU

2. 8-pin connector

   1. Consists of 2, 4-pin connections

   2. Used to power the CPU

Power Supply Unit

Converts alternating current electricity (AC) to Direct Current (DC) power, powering your PC components

Older models had to switch between 120-volt and 240-volt services, but newer models use Active Power Factor Correction (APFC), which detects and adjusts AC input

PSUs receive wattage ratings (a measure of how much power the PSU delivers in watts), as well as 80+ ratings, which determine the efficiency of the PSU when converting AC to DC power

Different voltages used by PCs

1. 12v

2. 5v

3. 3.3v

Storage Form Factors

1. 5.25” Form Factor

   1. Used by optical media

2. 3.5'“ Form Factor

   1. Form factor of HDDs

3. 2.5” Form Factor

   1. Used for SSDs

   2. Originally used in laptops

4. 1.8” Form Factor

   1. A less popular SSD format

5. M.2 Form Factor

   1. The most common SSD form factor

   2. 1st generation uses SATA interface, later generations are NVMe (Non-Volatile Memory Express)

      1. NVME are faster than SATA, as the CPU handles the job of the hard drive controller, leaving no interface between your CPU and storage

SCSI and ISCSI

1. Small Computer Systems Interface

   1. Uses a parallel interface

   2. You can connect numerous drives to a system

2. Internet SCSI

   1. Connect to your PC/Server via ethernet cable

RAID

Stands for Redundant Array of Inexpensive Disks. Multiple HDDs act as a single unit

There is hardware and software RAID forms

RAID goes from 0 - 6, but you can combine those to make different combinations

RAID 0

Striping

Minimum of 2 drive

Information is split and evenly distributed across the drives

Provides speed, but no safety for your data. If a drive dies, all data is lost

Raid 1

Mirroring

Minimum of 2 drives (adding more requires they be paired)

Data is stored identically on the drives

Provides redundancy, but slows performance

Raid 2

3 or 3+ drives needed

Data is split at the bit level across multiple disks and divided into blocks

Uses error correction known as Hamming code, introducing redundancy

Drives are synced by the controller to spin in unison, limited the ability to run multiple operations concurrently

RAID 3

Rarely used in practice

Minimum of 3 drives

Byte-level striping with a dedicated parity disk

RAID 4

Minimum of 3 drives

Block-level striping with a dedicated parity disk

RAID 5

Striping with parity

Minimum of 3 drives

Data is split across 2 drives, the third acts as parity, combining the data of 1 and 2

If 1 drive dies, the parity drive reverses the data storing operation on itself, getting the data from the dead drive back

Only 1 disk can die

Offers redundancy and speed

RAID 6

Minimum of 4 drives

RAID 6 is RAID 5, but with 2 parity drives, so 2 drives can be lost

RAID 10

Striping mirrors

Minimum of 4 drives (2 pairs)

Data is striped across the 2 data pairs, with each pair mirroring it’s partner

You can lose 1 drive from each pair. Losing a complete pair means your data is gone

RAID 0 + 1

Mirroring stripes

Minimum of 4 drives (2 pairs)

Data is striped between a drive pair and then mirror to the other drive pair

You can lose 1 device pair and still be okay

Losing the same striped device of each pair means your data is gone

How to do Encryption

1. File-based

2. Disk-based