Decoding the Power On Self Test (POST) Process:

Hey there, tech enthusiasts! Ever find yourself wondering how your computer runs through its checks before it boots up? Wonder no more! I'm your host, Professor JRod, ready to decode the power on self test (post) process for you. We'll examine how the BIOS validates your hardware's integrity and prepares your system for the operating system's loading. From the initialization of your CPU, including fetching the reset vector and setting the program counter, to in-depth discussions on memory testing, we're here to quench your technological thirst. Just consider the importance of a stable power supply and how post checks ensure that your computer operates optimally.

But that's not all! We're also delving into the technicalities of your computer's boot up sequence. Join us as we unravel the mysteries of the checksum verification and digital signatures that maintain the integrity of your BIOS code. We'll also explore how your system ensures it can provide video output to the display and the tests conducted to identify any potential graphic card or video memory issues. Rest assured, we are not skipping the critical expansion card checks that verify the functionality of your graphic cards, network cards, and more. By the end of our tech journey, you'll have a newfound understanding and appreciation of the vital checks your computer performs every time it's powered up. Let's get this tech party started!

Transcript

Speaker 1: 0:08

And welcome to Technology Tap. I'm Professor Jay Rock. In this episode we're going to talk about post power on self test. Let's get into it All right and welcome back everyone. Hope everybody had a wonderful, wonderful Thanksgiving and welcome back. Let's finish off the rest of the year strong. Right here is almost over 2023. It's almost in the books. We got about 34 days left as of today, November 27. And let's finish up the year strong.

Speaker 1: 1:29

So, for those of you who are listening for the first time, my name is Professor Jay Rod and I do these podcasts Based on the comp T exams. I go over topics, quick questions and answers and different stuff that comes up in the computer world as far as it relates to come to you and the company exam. So, like, if there's a new version of the exam coming out, I'll talk about that. If I get a hold of some questions, I'll drop them here in the podcast and then we go over different objectives in the exam. So one of the objectives of the exam is post right power off self test. The post is a diagnostic process performed by the vials during the boot up sequence of a computer. The primary purpose of post is to check the integrity of essential hardware components and ensure that the system is in a suitable state for the operating system to load. And we're going to give a breakdown of the post process.

Speaker 1: 2:27

Initialization of CPU the initialization of the CPU during post involves preparing the central processing unit for operation. This process is assures that the CPU starts in a known state and is ready to execute instructions. Here are the key steps involved in initialization of the CPU during post reset operation. When the computer is powered on or or restarted, a reset signal sends CPU. The CPU initializes itself by resetting its external state to a predefined starting point. Fetching reset vector the CPU fetches the reset vector. A reset vector is a memory address with the initial program counter value is stored. The program counter is a register in the CPU that keeps track of the memory address of the next instructions to be executed. Setting the program counter the CPU sets the program counter with the value fetch from the reset vector. This determines the starting point in memory for the execution of instructions.

Speaker 1: 3:28

Initialization of registers the CPU initializes its general purpose registers to known values. Specific registers may be set to default values or cleared to ensure a clean state. Setting flags the CPU status flags, such as zero flag, carry the flag and overflow flags are typically set to the default values. These flags are used to indicate the outcome of a rhythmic and logical operations. Mode settings depending on the CPU architecture, the process may operate in different modes, for example real mode or protected mode. The CPU sets its mode to initial state, determining how it interacts with memory and other system components. Initializing control registers control registers, which configure the various aspects of the CPU operations, are initialized to default values. These may include registers that control memory management, interrupt handling and other systems level functions.

Speaker 1: 4:25

Self-test and diagnose checks the CPU may perform self-test and diagnose check during initialization to ensure that internal components are functioning correctly. Any errors detected during these checks may result in an error message or diagnostic code. By the end of the CPU initialization process, the processors, in the state way, can start executing instructions from the system firmware or bootloader. The overall goal is to establish a reliable and consistent starting point in the CPU operation, ensuring that subsequent instructions are executed correctly as part of the BUDO sequence.

Speaker 1: 5:01

Next we're going to talk about memory testing. Memory testing is a crucial component of the Power On Self test performed by the computer during the BUDO process. The purpose of the memory test is to check the integrity of the system's RAM. Random access memory Remember RAM is volatile memory that stores data and machine code currently being used and accessed by the computer's processor. Here's an overview of it.

Speaker 1: 5:26

Memory address check the post starts by testing different memory address to ensure that the RAM is accessible. It writes specific patterns of data to different memory locations and then reads the data back to verify correctness. Data bus test the data bus is the communication pathway between the CPU and the RAM. The memory test checks the data bus by writing data to the RAM and then reading it back to ensure that the data is transferred correctly. Address bus test the address bus is responsible for specifying a memory address. The post test the address bus by verifying that the CPU can correctly address different locations. In the RAM Pattern test. The memory test often uses specific patterns, such as all zeros or ones alternating patterns to write and to read from memory. This helps identify issues with specific bits or cells in the memory Walking bit test. This test involves writing a specific bit pattern to memory and then shifting the bit pattern to the next memory location. It helps detect stuck or faulty bits in memory.

Speaker 1: 6:29

Checkerboard test. The checkerboard test alternates between writing patterns to odd and even memory address. It helps identify issues with adjacent memory locations. March test March test involves a sequence of reading and writing operations that transverse throughout the memory. Tests like March C and March B are variations designed to detect different type of memory faults. Bit flip test the bit flip test can intentionally flip individual bits in memory to check that the memory can correctly store and retrieve the altered data. And memory size detection the post may also detect and verify the amount of memory installed to ensure the system recognize the correct memory size. If errors are detected during memory tests, the post typically generates error messages or beep codes providing information about the nature and the location of the memory issues. Users or technicians can use this information to diagnose and address hardware problems. A successful test is critical to ensuring the stability and reliability of the computer systems, as faulty RAM can lead to a priority of issues, including system crashes, data corruptions and unprecedented behavior.

Speaker 1: 7:44

Power supply checks A power supply checks are essential part of the post and overall system diagnostic. Stable and reliable power supply is critical for the proper functioning of a computer system. Here are some common power supply checks performed during post Voltage railing monitor the power supply unit provides different voltage level, commonly 12 volt, 5 volt and 3.3, to various components in the system. The post may check the voltage of these rails to ensure that they are within acceptable tolerance levels. Deviation from the specific voltage levels can indicate power supply issues. Power good signal the power supply generates a power good signal to indicate that all power rails are stable and within the specific voltage range. The system wait for the signal before proceeding with the boot process. The power good signal is not received, as system may halt to prevent potential damage.

Speaker 1: 8:42

Overvoltage and undervoltage protection the power supply may have built-in protection mechanisms to prevent overvoltage or undervoltage situations. The post checks for overvoltage or undervoltage conditions and takes appropriate actions to safeguard the components. Short circuit protection Power supply often includes short circuit protection to prevent damage in the event of a short circuit in the system. The post may check for short circuits and respond accordingly. Power supply fan check. The post may check whether the fan in the power supply is operational. A malfunctioning fan can lead to overheating and the system may halt or generate warnings if the fan is not working properly.

Speaker 1: 9:22

Power on delay Some systems incorporate a power on delay to ensure that the power supply stabilizes before other components start operating. This delay helps prevent issues that could arise from unstable power supply during the initial moments of powering. On Load test, the post may perform load tests to check how well the power supply handles various load Fluctuation in power. Demand, such as the startup of components, should be handled smoothly by the power supply Power factor correction check. Some power supplies include power factor correction to improve the efficiency of power usage. The polls may check whether the PFC is functioning properly. If any issues are detected during the power supply checks, the polls may generate errors messages, beep codes or other indicators to alert users or technicians about possible problems. Addressing power supply issues is crucial to ensure systems to literally improve and damage to other components. If you suspect power problems, it is recommended that you consult a system documentation and seek assistance from a technician support or a qualified technician.

Speaker 1: 10:32

Next is an initialization of input-output devices, and this is a crucial step of post during the boot-up sequence of a computer. The IO devices include peripherals such as keyboard, mouse, storage devices and other external devices connected to the computer. The initialization of these devices ensure they are recognized and operational. Here's an overview Immerating devices the system BIOS begins by enumerating and identifying the IO devices connected to the system. This process involves identifying the type and the location of each device. Initializing system bus the system bus PCI, pcie that connected the CPU to various IO devices are initialized. This involves configuring the bus and ensuring proper communication between the CPU and the connected devices. Assigning resources the BIOS, or UEFI, assigns system resources, such as IRQs, interrupt requests if you don't know what that is IO addresses and memory address to each IO device. This allocation ensures that devices can operate without conflicting with each other.

Speaker 1: 11:40

Testing IO device the POST performs basic tests on each IO device to ensure they are functioning. For example, the system may check whatever keyboard and a mouse respond to input or if the storage device can be accessed. Loading device drivers the system firmware may load basic device drivers for the central IO device, enabling communication between the operating system and these devices. How are you gonna use the keyboard right? If you wanna go into the BIOS, it has to have some kind of drivers loaded, right. This is where it does it. This is often the primary step to ensure that critical devices can be accessed during the boot process. Detecting bootable devices the systems identify and prioritize bootable devices such as hard drives, solid state drives or optical drives. The BIOS, or UEFI, determines the device from which the operating system will be loaded.

Speaker 1: 12:30

Initializing mass storage devices Mass storage devices, such as hard drive or SSD drive undergo initialization checks to ensure they are responsive and accessible. The system may check the presence of valid boot record on these devices. Initializing display devices display devices such as graphic cards and monitors are initialized to enable video output. The system sets display resolution and refresh rates based on the capabilities of the connected monitor. Loading expansion card firmware If there are expansion cards in the system, for example graphic cards, network cards, their firmware may be loaded and initialized. This ensures that additional functionality provided by these cards is available to the system. And then, finally, network initialization If the system has integrated or add on network interfaces, the firmware may initialize these interfaces. This enables network communication and it may involve containing IP address through DHCP. So when you're obtaining an IP address from DHCP, this is where it does it. At this point, again, if any issues are detected during initialization of IO devices, the post may generate error messages, because all display diagnostic information to indicate the nature of the proper Proper initialization of the IO devices is essential for successful booting of the operating system and the overall functionality of the computer system.

Speaker 1: 14:04

Next we go to Biles integrity check. The integrity check is a critical step in the power on self-test process during the computer's bootup sequence. The Biles is a firmware that resides on a chip on a motherboard and it provides low level control for the hardware components on the computer. Ensuring the integrity of the Biles is critical for the system's stability and proper functioning. Here's an overview of the Biles integrity check.

Speaker 1: 14:35

Rom Reno memory check. The BIOS is typically stored in a non-biotel memory chip, often referred to as ROM, read-only memory or flash memory. During the process, the system checks the integrity of the BIOS stored in ROM. This involves reading the BIOS code from memory and verifying its integrity Check. Some verification the BIOS code is often accompanied by a checksum or hash value, which is a mathematical sum calculated based on the contents of the BIOS. The post performs a checksum verification to ensure that the calculated checksum matches the expected value. If the checksum does not match, it suggests that the BIOS code may be corrupt or modified. Digital signature if applicable. Some modern systems may use digital signatures to verify the authenticity and integrity of the BIOS code. A digital signature is a cryptographic mechanism that ensures that the code has not been tampered with. The BIOS may contain a digital signature and the post checks its validity.

Speaker 1: 15:37

Boot block integrity check the BIOS typically has a small portion known as boot block that is responsible for essential functions, including the initial stages of the boot process. The integrity of the boot block is checked to ensure that critical functions such as reading from storage devices are intact. Error handling If any issues are detected during the BIOS integrity check, the post may generate errors and beep codes or displays information indicating a problem. Error messages may provide details about the nature of the issue, such as a checksum mismatch or corrupted BIOS, and then BIOS recovery, if it's available. Some systems are equipped with BIOS recovery mechanism that can be activated if the primary BIOS is found to be corrupt. In the event of the BIOS integrity failure, the system may attempt to recover using a backup copy of the BIOS or initiated process to flash the BIOS. Ensuring the integrity of the BIOS is critical because the BIOS plays a fundamental role in the early stages of the boot process. If the BIOS is compromised or corrupt, it can lead to systemic abilities failures or an inability to boot. The operating system Manufacturers often provide tools and procedures for updating or recovering the BIOS in case of issues, emphasizing the importance of maintaining BIOS integrity.

Speaker 1: 17:01

Next we're going to do expansion cards. Expansion card checks are part of the post process that occurs during computed boot up sequence. Expansion cards are additional hardware components such as graphic cards, network cards, sound cards and other peripherals that can be installed in expansion slots on the motherboard. The post verifies the presence and functionality of these expansion cards to ensure proper system operation. Here's an overview Presence detection the post checks for the presence of expansion cards in their respective slots on the motherboard. It detects the type and number of expansion cards installed.

Speaker 1: 17:41

Initialization of integrated circuits Each expansion card contains integrated circuits responsible for a specific function. The post initializes these ICs to ensure they're ready for operation. Testing for basic functionality the post performs basic tests to ensure that each expansion card is functioning correctly. For example, a graphic card may be tested for video output, a network card for network connectivity or a sound card for audio output. Address address assignments the system assigns addresses, interrupts and other resources to each expansion card. To prevent conflicts, the post ensures that these assignments are made correctly and do not overlap with other devices. Rq handling or interrupt request handling Expansion cards often use interrupts to communicate with the CPU. The post checks the RQ settings for each expansion card to prevent conflicts and ensure proper communications. It is very rare nowadays, ladies and gentlemen, that you get an RQ conflict. Back in the day it was common Every time you put an expansion card in you had to worry about RQs, but nowadays you don't.

Speaker 1: 18:50

Expansion ROM initialization Some expansion cards have built-in firmware or expansion ROMs that provide additional functionality. The post initializes expansion ROMs to make sure they're accessible and operational. Air detection and reporting If any issues are detected during the expansion card check, the post may generate error messages, beep codes and display diagnostic information. Error messages help identify the specific expansion card causing the problem. Graphic card initialization the initialization of a graphic card is a critical part of the expansion card check. The post ensures that the graphic card is operational and capable of providing video output to the display. Boodlewood device identification Some expansion cards, such as storage controllers, may be responsible for connecting to bootable devices, for example hard drives. The post identifies and verifies the presence of these bootable devices. Numeric interface initialization If a network interface card is present, the post initializes it to enable network connectivity. This may involve obtaining an IP address through the HCP. The expansion card checks are important for ensuring that all components of the system are properly detected and initialized during the boot process. Any issues identified during this phrase or this phase can be critical for digusting and resolving hardware related problems. If there are problems with specific expansion cards, users may need to reset, take it out and put it back or replace the card, update firmware or drivers or address any conflict in the system's configuration.

Speaker 1: 20:33

Next we're going to go with the display test. It's a little bit more expanding on the monitor and the graphics card. The display test is a critical component of post-process during the computer's boot up sequence. This test focuses on verifying the functionality of the display subsystem, which includes the graphic card, the monitor and related components. The primary goal is to ensure that the system can provide a video output to the display and the display is capable of presenting information to the user. Here's an overview.

Speaker 1: 21:05

Our graphic card initialization the post begins by initializing the graphic card, which is responsible for rendering images and sending them to the display. This involves configuring the graphics card and ensuring that it's operational. Checking video memory the post may perform a quick test of the video memory on the graphic card to ensure that it's functioning correctly. Any issues with the video memory can lead to graphical artifacts or display issues. Setting display parameters the system configures the display parameters, such as screen resolution, refresh rate, based on default settings or user defined preferences so that in the bios you can find output to display the post and signals of display instructing it to show specific patterns or information. This allows the systems to verify the display is receiving signals and can present information. Color and pixel text. The display makes sure series of colors, patterns or pixel grids to ensure that each pixel on the screen is functional. This helps identify any dead pixels or abnormalities in that display.

Speaker 1: 22:10

Testing multiple monitors If you have more than one systems will multiple monitors may undergo tests to ensure that all connected devices are functioning as expected. This includes checking for corrected, correct detection and configuration and multiple display outputs. User interface elements some system display basic user interface elements during the post, such as manufacturers logo, system information or diagnostic message. This provides visual feedback to the user and indicate that the display system is operational. Error messages and beep codes If any systems are detected during the display test, the post may generate error messages, beep codes and or other visual indicators to alert the users. These indicators can help diagnose the problem with graphical with the graphical cards, monitor or display connections.

Speaker 1: 23:00

External display checks. For systems with external display connections HDMI or display port the post may check the functionality of these connectors and the corresponding signals. The display test is critical because it can confirm that a computer can communicate with the display hardware, providing a visual interface for the user. If the issues are identified during the test, users may need to check the display connections, test with different monitor or cable, or troubleshooting problems with the graphic cards or its drivers. The visual feedback provided during the display test is valuable for diagnostic and resolving potential display related issues. Next we have and this is probably going to be the last one storage device.

Speaker 1: 23:48

Storage device checks are in integral part of post process during the computer boot up sequence. These checks are designed to verify the presence, integrity and functionality of stored devices, such as hard drive, solid state drives and other storage peripherals. Here's the overview of the storage devices check during post detecting attached storage the post begins by detecting and identifying the storage device connected to the system. This includes internal drives, external drives and other storage peripherals. Initialization of storage controllers the storage controllers, which manage data transfer between storage devices and the rest of the systems, are initialized. This involves checking the integrity of the controller and ensuring it is ready to communicate with the attached storage devices. Checking storage device power and connection the post verifies that the power supply and data connections to the storage device are stable and correctly configured. Loose cables or power issues can lead to storage device failures.

Speaker 1: 24:50

Smart self monitoring, analysis and reporting technology checks If supported by the storage device, the post may query smart data to assess the help of the drives. Smart checks can identify potential issues with the drives, such as bad sectors or imminent drive failure. Bios UEFI recognition the post ensures that the system bios or UEFI recognizes storage device. The bios UEFI provides information about the connected drives and their basic configurations. Boot sector and partition checks the post checks the boot sector and partition information of bootable drives to ensure that they are correctly configured. If the system is configured to boot from a specific drive, the post verifies that the drive contains a valid boot loader.

Speaker 1: 25:39

Read write test Basic read and write test may be performed on the storage device to ensure that data can be properly written to and read from devices. These tests help identify issues with data integrity and storage device. Raid configuration checks if applicable. In a system with a RAID, which is redundant array of independent disk configurations, the post verifies the status and the integrity of the RAID arrays. This includes checking for fail drives and ensuring that the RAID configuration is consistent. Error handling If any issues are detected during the storage device check, the post may generate error messages because of display diagnostic information. These indicators help identify the nature of the storage related problem, Loading storage device data if needed. If specific storage devices are required for proper operation, the post may load these devices to enable connections between the operating system and the storage device. Ensuring the proper functioning of storage devices is critical for the successful booting of the operating system and the overall stability. If the storage device issues are identified during the post, users may need to check cables, replace faulty drives, update firmware or address configuration problems to ensure reliable storage performance.

Speaker 1: 27:08

Now there is a couple of more. I might have to do a part two on this because there's uh, uh, that's not too many, that's probably like two left. Uh, I just don't like to do a lot. I think sometimes if I do too much, uh, it's already. You know I don't want to do too much and it might, it might bore you, so I'm going to do a part two. I'll do a part two on this, um, one day. But yeah, and it's amazing that it does all this, and what? In a matter of seconds, right, two, three seconds it takes to do all the stuff that I just told you. Right, the computer does it before the computer goes into, you know, before you can log in to Windows, right? So it's it's pretty amazing that it does all this stuff. Now, um, you know, all this thing is is is something that will be on the Compti exam. Some of the stuff would not be, I think, in the beginning, but it was good about the CPU, but it was a good thing to learn. A lot of this stuff is on the Compti at the A plus exam, so it's a good foundation to know, right, and, yeah, so that's going to put a wrap on this show. Thank you so much for listening and I hope you learned something today, especially about posts until next time.

Speaker 1: 28:53

This has been a presentation of Little Chacha Productions. Art by Joachim. Music by Art by Sarah. Music by Joachim. If you want to get in contact with me, you can. My email address is ProfessorJRotjrod at gmailcom. I'm also at Instagram at Professor J Rod.