November 27, 2023 • 29 mins
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!
If you want to help me with my research please e-mail me.
Professorjrod@gmail.com
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Professorjrod@gmail.com
Art By Sarah/Desmond
Music by Joakim Karud
Little chacha Productions
Juan Rodriguez can be reached at
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Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:08):
And welcome to Technology Tap.
(00:29):
I'm Professor Jay Rock.
In this episode we're going totalk about post power on self
(00:56):
test.
Let's get into it All right andwelcome back everyone.
Hope everybody had a wonderful,wonderful Thanksgiving and
welcome back.
Let's finish off the rest ofthe year strong.
(01:17):
Right here is almost over 2023.
It's almost in the books.
We got about 34 days left as oftoday, November 27.
And let's finish up the yearstrong.
So, for those of you who arelistening for the first time, my
name is Professor Jay Rod and Ido these podcasts Based on the
(01:37):
comp T exams.
I go over topics, quickquestions and answers and
different stuff that comes up inthe computer world as far as it
relates to come to you and thecompany exam.
So, like, if there's a newversion of the exam coming out,
I'll talk about that.
If I get a hold of somequestions, I'll drop them here
(01:58):
in the podcast and then we goover different objectives in the
exam.
So one of the objectives of theexam is post right power off
self test.
The post is a diagnosticprocess performed by the vials
during the boot up sequence of acomputer.
The primary purpose of post isto check the integrity of
essential hardware componentsand ensure that the system is in
(02:20):
a suitable state for theoperating system to load.
And we're going to give abreakdown of the post process.
Initialization of CPU theinitialization of the CPU during
post involves preparing thecentral processing unit for
operation.
This process is assures thatthe CPU starts in a known state
and is ready to executeinstructions.
(02:41):
Here are the key steps involvedin initialization of the CPU
during post reset operation.
When the computer is powered onor or restarted, a reset signal
sends CPU.
The CPU initializes itself byresetting its external state to
a predefined starting point.
Fetching reset vector the CPUfetches the reset vector.
(03:03):
A reset vector is a memoryaddress with the initial program
counter value is stored.
The program counter is aregister in the CPU that keeps
track of the memory address ofthe next instructions to be
executed.
Setting the program counter theCPU sets the program counter
with the value fetch from thereset vector.
This determines the startingpoint in memory for the
(03:25):
execution of instructions.
Initialization of registers theCPU initializes its general
purpose registers to knownvalues.
Specific registers may be setto default values or cleared to
ensure a clean state.
Setting flags the CPU statusflags, such as zero flag, carry
the flag and overflow flags aretypically set to the default
(03:48):
values.
These flags are used toindicate the outcome of a
rhythmic and logical operations.
Mode settings depending on theCPU architecture, the process
may operate in different modes,for example real mode or
protected mode.
The CPU sets its mode toinitial state, determining how
it interacts with memory andother system components.
(04:08):
Initializing control registerscontrol registers, which
configure the various aspects ofthe CPU operations, are
initialized to default values.
These may include registersthat control memory management,
interrupt handling and othersystems level functions.
Self-test and diagnose checksthe CPU may perform self-test
(04:29):
and diagnose check duringinitialization to ensure that
internal components arefunctioning correctly.
Any errors detected duringthese checks may result in an
error message or diagnostic code.
By the end of the CPUinitialization process, the
processors, in the state way,can start executing instructions
from the system firmware orbootloader.
The overall goal is toestablish a reliable and
(04:52):
consistent starting point in theCPU operation, ensuring that
subsequent instructions areexecuted correctly as part of
the BUDO sequence.
Next we're going to talk aboutmemory testing.
Memory testing is a crucialcomponent of the Power On Self
test performed by the computerduring the BUDO process.
The purpose of the memory testis to check the integrity of the
(05:13):
system's RAM.
Random access memory RememberRAM is volatile memory that
stores data and machine codecurrently being used and
accessed by the computer'sprocessor.
Here's an overview of it.
Memory address check the poststarts by testing different
memory address to ensure thatthe RAM is accessible.
It writes specific patterns ofdata to different memory
(05:34):
locations and then reads thedata back to verify correctness.
Data bus test the data bus isthe communication pathway
between the CPU and the RAM.
The memory test checks the databus by writing data to the RAM
and then reading it back toensure that the data is
transferred correctly.
Address bus test the addressbus is responsible for
specifying a memory address.
(05:55):
The post test the address busby verifying that the CPU can
correctly address differentlocations.
In the RAM Pattern test.
The memory test often usesspecific patterns, such as all
zeros or ones alternatingpatterns to write and to read
from memory.
This helps identify issues withspecific bits or cells in the
(06:16):
memory Walking bit test.
This test involves writing aspecific bit pattern to memory
and then shifting the bitpattern to the next memory
location.
It helps detect stuck or faultybits in memory.
Checkerboard test.
The checkerboard testalternates between writing
patterns to odd and even memoryaddress.
It helps identify issues withadjacent memory locations.
(06:39):
March test March test involvesa sequence of reading and
writing operations thattransverse throughout the memory
.
Tests like March C and March Bare variations designed to
detect different type of memoryfaults.
Bit flip test the bit flip testcan intentionally flip
individual bits in memory tocheck that the memory can
correctly store and retrieve thealtered data.
(07:00):
And memory size detection thepost may also detect and verify
the amount of memory installedto ensure the system recognize
the correct memory size.
If errors are detected duringmemory tests, the post typically
generates error messages orbeep codes providing information
about the nature and thelocation of the memory issues.
(07:22):
Users or technicians can usethis information to diagnose and
address hardware problems.
A successful test is criticalto ensuring the stability and
reliability of the computersystems, as faulty RAM can lead
to a priority of issues,including system crashes, data
corruptions and unprecedentedbehavior.
(07:44):
Power supply checks A powersupply checks are essential part
of the post and overall systemdiagnostic.
Stable and reliable powersupply is critical for the
proper functioning of a computersystem.
Here are some common powersupply checks performed during
post Voltage railing monitor thepower supply unit provides
(08:06):
different voltage level,commonly 12 volt, 5 volt and 3.3
, to various components in thesystem.
The post may check the voltageof these rails to ensure that
they are within acceptabletolerance levels.
Deviation from the specificvoltage levels can indicate
power supply issues.
Power good signal the powersupply generates a power good
(08:27):
signal to indicate that allpower rails are stable and
within the specific voltagerange.
The system wait for the signalbefore proceeding with the boot
process.
The power good signal is notreceived, as system may halt to
prevent potential damage.
Overvoltage and undervoltageprotection the power supply may
have built-in protectionmechanisms to prevent
(08:48):
overvoltage or undervoltagesituations.
The post checks for overvoltageor undervoltage conditions and
takes appropriate actions tosafeguard the components.
Short circuit protection Powersupply often includes short
circuit protection to preventdamage in the event of a short
circuit in the system.
The post may check for shortcircuits and respond accordingly
.
Power supply fan check.
(09:11):
The post may check whether thefan in the power supply is
operational.
A malfunctioning fan can leadto overheating and the system
may halt or generate warnings ifthe fan is not working properly
.
Power on delay Some systemsincorporate a power on delay to
ensure that the power supplystabilizes before other
components start operating.
This delay helps prevent issuesthat could arise from unstable
(09:33):
power supply during the initialmoments of powering.
On Load test, the post mayperform load tests to check how
well the power supply handlesvarious load Fluctuation in
power.
Demand, such as the startup ofcomponents, should be handled
smoothly by the power supplyPower factor correction check.
(09:54):
Some power supplies includepower factor correction to
improve the efficiency of powerusage.
The polls may check whether thePFC is functioning properly.
If any issues are detectedduring the power supply checks,
the polls may generate errorsmessages, beep codes or other
indicators to alert users ortechnicians about possible
problems.
(10:15):
Addressing power supply issuesis crucial to ensure systems to
literally improve and damage toother components.
If you suspect power problems,it is recommended that you
consult a system documentationand seek assistance from a
technician support or aqualified technician.
Next is an initialization ofinput-output devices, and this
(10:37):
is a crucial step of post duringthe boot-up sequence of a
computer.
The IO devices includeperipherals such as keyboard,
mouse, storage devices and otherexternal devices connected to
the computer.
The initialization of thesedevices ensure they are
recognized and operational.
Here's an overview Immeratingdevices the system BIOS begins
(11:00):
by enumerating and identifyingthe IO devices connected to the
system.
This process involvesidentifying the type and the
location of each device.
Initializing system bus thesystem bus PCI, pcie that
connected the CPU to various IOdevices are initialized.
This involves configuring thebus and ensuring proper
communication between the CPUand the connected devices.
(11:23):
Assigning resources the BIOS,or UEFI, assigns system
resources, such as IRQs,interrupt requests if you don't
know what that is IO addressesand memory address to each IO
device.
This allocation ensures thatdevices can operate without
conflicting with each other.
Testing IO device the POSTperforms basic tests on each IO
(11:43):
device to ensure they arefunctioning.
For example, the system maycheck whatever keyboard and a
mouse respond to input or if thestorage device can be accessed.
Loading device drivers thesystem firmware may load basic
device drivers for the centralIO device, enabling
communication between theoperating system and these
devices.
How are you gonna use thekeyboard right?
(12:05):
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 stepto ensure that critical devices
can be accessed during the bootprocess.
Detecting bootable devices thesystems identify and prioritize
bootable devices such as harddrives, solid state drives or
optical drives.
The BIOS, or UEFI, determinesthe device from which the
(12:28):
operating system will be loaded.
Initializing mass storagedevices Mass storage devices,
such as hard drive or SSD driveundergo initialization checks to
ensure they are responsive andaccessible.
The system may check thepresence of valid boot record on
these devices.
Initializing display devicesdisplay devices such as graphic
(12:49):
cards and monitors areinitialized to enable video
output.
The system sets displayresolution and refresh rates
based on the capabilities of theconnected monitor.
Loading expansion card firmwareIf there are expansion cards in
the system, for example graphiccards, network cards, their
firmware may be loaded andinitialized.
(13:11):
This ensures that additionalfunctionality provided by these
cards is available to the system.
And then, finally, networkinitialization If the system has
integrated or add on networkinterfaces, the firmware may
initialize these interfaces.
This enables networkcommunication and it may involve
(13:31):
containing IP address throughDHCP.
So when you're obtaining an IPaddress from DHCP, this is where
it does it.
At this point, again, if anyissues are detected during
initialization of IO devices,the post may generate error
messages, because all displaydiagnostic information to
(13:53):
indicate the nature of theproper Proper initialization of
the IO devices is essential forsuccessful booting of the
operating system and the overallfunctionality of the computer
system.
Next we go to Biles integritycheck.
The integrity check is acritical step in the power on
(14:13):
self-test process during thecomputer's bootup sequence.
The Biles is a firmware thatresides on a chip on a
motherboard and it provides lowlevel control for the hardware
components on the computer.
Ensuring the integrity of theBiles is critical for the
system's stability and properfunctioning.
Here's an overview of the Bilesintegrity check.
(14:35):
Rom Reno memory check.
The BIOS is typically stored ina non-biotel memory chip, often
referred to as ROM, read-onlymemory or flash memory.
During the process, the systemchecks the integrity of the BIOS
stored in ROM.
This involves reading the BIOScode from memory and verifying
its integrity Check.
Some verification the BIOS codeis often accompanied by a
(14:58):
checksum or hash value, which isa mathematical sum calculated
based on the contents of theBIOS.
The post performs a checksumverification to ensure that the
calculated checksum matches theexpected value.
If the checksum does not match,it suggests that the BIOS code
may be corrupt or modified.
Digital signature if applicable.
(15:19):
Some modern systems may usedigital signatures to verify the
authenticity and integrity ofthe BIOS code.
A digital signature is acryptographic mechanism that
ensures that the code has notbeen tampered with.
The BIOS may contain a digitalsignature and the post checks
its validity.
Boot block integrity check theBIOS typically has a small
(15:41):
portion known as boot block thatis responsible for essential
functions, including the initialstages of the boot process.
The integrity of the boot blockis checked to ensure that
critical functions such asreading from storage devices are
intact.
Error handling If any issuesare detected during the BIOS
integrity check, the post maygenerate errors and beep codes
(16:04):
or displays informationindicating a problem.
Error messages may providedetails about the nature of the
issue, such as a checksummismatch or corrupted BIOS, and
then BIOS recovery, if it'savailable.
Some systems are equipped withBIOS recovery mechanism that can
be activated if the primaryBIOS is found to be corrupt.
(16:24):
In the event of the BIOSintegrity failure, the system
may attempt to recover using abackup copy of the BIOS or
initiated process to flash theBIOS.
Ensuring the integrity of theBIOS is critical because the
BIOS plays a fundamental role inthe early stages of the boot
process.
If the BIOS is compromised orcorrupt, it can lead to systemic
(16:45):
abilities failures or aninability to boot.
The operating systemManufacturers often provide
tools and procedures forupdating or recovering the BIOS
in case of issues, emphasizingthe importance of maintaining
BIOS integrity.
Next we're going to do expansioncards.
Expansion card checks are partof the post process that occurs
(17:07):
during computed boot up sequence.
Expansion cards are additionalhardware components such as
graphic cards, network cards,sound cards and other
peripherals that can beinstalled in expansion slots on
the motherboard.
The post verifies the presenceand functionality of these
expansion cards to ensure propersystem operation.
Here's an overview Presencedetection the post checks for
(17:31):
the presence of expansion cardsin their respective slots on the
motherboard.
It detects the type and numberof expansion cards installed.
Initialization of integratedcircuits Each expansion card
contains integrated circuitsresponsible for a specific
function.
The post initializes these ICsto ensure they're ready for
(17:52):
operation.
Testing for basic functionalitythe post performs basic tests
to ensure that each expansioncard is functioning correctly.
For example, a graphic card maybe tested for video output, a
network card for networkconnectivity or a sound card for
audio output.
Address address assignments thesystem assigns addresses,
(18:13):
interrupts and other resourcesto each expansion card.
To prevent conflicts, the postensures that these assignments
are made correctly and do notoverlap with other devices.
Rq handling or interruptrequest handling Expansion cards
often use interrupts tocommunicate with the CPU.
The post checks the RQ settingsfor each expansion card to
(18:34):
prevent conflicts and ensureproper communications.
It is very rare nowadays,ladies and gentlemen, that you
get an RQ conflict.
Back in the day it was commonEvery time you put an expansion
card in you had to worry aboutRQs, but nowadays you don't.
Expansion ROM initializationSome expansion cards have
built-in firmware or expansionROMs that provide additional
(18:56):
functionality.
The post initializes expansionROMs to make sure they're
accessible and operational.
Air detection and reporting Ifany issues are detected during
the expansion card check, thepost may generate error messages
, beep codes and displaydiagnostic information.
Error messages help identifythe specific expansion card
causing the problem.
(19:17):
Graphic card initialization theinitialization of a graphic
card is a critical part of theexpansion card check.
The post ensures that thegraphic card is operational and
capable of providing videooutput to the display.
Boodlewood deviceidentification Some expansion
cards, such as storagecontrollers, may be responsible
(19:38):
for connecting to bootabledevices, for example hard drives
.
The post identifies andverifies the presence of these
bootable devices.
Numeric interfaceinitialization If a network
interface card is present, thepost initializes it to enable
network connectivity.
This may involve obtaining anIP address through the HCP.
(19:59):
The expansion card checks areimportant for ensuring that all
components of the system areproperly detected and
initialized during the bootprocess.
Any issues identified duringthis phrase or this phase can be
critical for digusting andresolving hardware related
problems.
If there are problems withspecific expansion cards, users
(20:21):
may need to reset, take it outand put it back or replace the
card, update firmware or driversor address any conflict in the
system's configuration.
Next we're going to go with thedisplay test.
It's a little bit moreexpanding on the monitor and the
graphics card.
The display test is a criticalcomponent of post-process during
(20:42):
the computer's boot up sequence.
This test focuses on verifyingthe functionality of the display
subsystem, which includes thegraphic card, the monitor and
related components.
The primary goal is to ensurethat the system can provide a
video output to the display andthe display is capable of
presenting information to theuser.
Here's an overview.
(21:05):
Our graphic card initializationthe post begins by initializing
the graphic card, which isresponsible for rendering images
and sending them to the display.
This involves configuring thegraphics card and ensuring that
it's operational.
Checking video memory the postmay perform a quick test of the
video memory on the graphic cardto ensure that it's functioning
(21:26):
correctly.
Any issues with the videomemory can lead to graphical
artifacts or display issues.
Setting display parameters thesystem configures the display
parameters, such as screenresolution, refresh rate, based
on default settings or userdefined preferences so that in
the bios you can find output todisplay the post and signals of
display instructing it to showspecific patterns or information
(21:49):
.
This allows the systems toverify the display is receiving
signals and can presentinformation.
Color and pixel text.
The display makes sure seriesof colors, patterns or pixel
grids to ensure that each pixelon the screen is functional.
This helps identify any deadpixels or abnormalities in that
(22:09):
display.
Testing multiple monitors If youhave more than one systems will
multiple monitors may undergotests to ensure that all
connected devices arefunctioning as expected.
This includes checking forcorrected, correct detection and
configuration and multipledisplay outputs.
User interface elements somesystem display basic user
(22:30):
interface elements during thepost, such as manufacturers logo
, system information ordiagnostic message.
This provides visual feedbackto the user and indicate that
the display system isoperational.
Error messages and beep codesIf any systems are detected
during the display test, thepost may generate error messages
, beep codes and or other visualindicators to alert the users.
(22:52):
These indicators can helpdiagnose the problem with
graphical with the graphicalcards, monitor or display
connections.
External display checks.
For systems with externaldisplay connections HDMI or
display port the post may checkthe functionality of these
connectors and the correspondingsignals.
The display test is criticalbecause it can confirm that a
(23:14):
computer can communicate withthe display hardware, providing
a visual interface for the user.
If the issues are identifiedduring the test, users may need
to check the display connections, test with different monitor or
cable, or troubleshootingproblems with the graphic cards
or its drivers.
The visual feedback providedduring the display test is
(23:36):
valuable for diagnostic andresolving potential display
related issues.
Next we have and this isprobably going to be the last
one storage device.
Storage device checks are inintegral part of post process
during the computer boot upsequence.
These checks are designed toverify the presence, integrity
(23:59):
and functionality of storeddevices, such as hard drive,
solid state drives and otherstorage peripherals.
Here's the overview of thestorage devices check during
post detecting attached storagethe post begins by detecting and
identifying the storage deviceconnected to the system.
This includes internal drives,external drives and other
(24:19):
storage peripherals.
Initialization of storagecontrollers the storage
controllers, which manage datatransfer between storage devices
and the rest of the systems,are initialized.
This involves checking theintegrity of the controller and
ensuring it is ready tocommunicate with the attached
storage devices.
Checking storage device powerand connection the post verifies
(24:40):
that the power supply and dataconnections to the storage
device are stable and correctlyconfigured.
Loose cables or power issuescan lead to storage device
failures.
Smart self monitoring, analysisand reporting technology checks
If supported by the storagedevice, the post may query smart
data to assess the help of thedrives.
(25:02):
Smart checks can identifypotential issues with the drives
, such as bad sectors orimminent drive failure.
Bios UEFI recognition the postensures that the system bios or
UEFI recognizes storage device.
The bios UEFI providesinformation about the connected
drives and their basicconfigurations.
(25:22):
Boot sector and partitionchecks the post checks the boot
sector and partition informationof bootable drives to ensure
that they are correctlyconfigured.
If the system is configured toboot from a specific drive, the
post verifies that the drivecontains a valid boot loader.
Read write test Basic read andwrite test may be performed on
(25:42):
the storage device to ensurethat data can be properly
written to and read from devices.
These tests help identifyissues with data integrity and
storage device.
Raid configuration checks ifapplicable.
In a system with a RAID, whichis redundant array of
independent disk configurations,the post verifies the status
(26:05):
and the integrity of the RAIDarrays.
This includes checking for faildrives and ensuring that the
RAID configuration is consistent.
Error handling If any issuesare detected during the storage
device check, the post maygenerate error messages because
of display diagnosticinformation.
These indicators help identifythe nature of the storage
(26:29):
related problem, Loading storagedevice data if needed.
If specific storage devices arerequired for proper operation,
the post may load these devicesto enable connections between
the operating system and thestorage device.
Ensuring the proper functioningof storage devices is critical
(26:49):
for the successful booting ofthe operating system and the
overall stability.
If the storage device issuesare identified during the post,
users may need to check cables,replace faulty drives, update
firmware or addressconfiguration problems to ensure
reliable storage performance.
Now there is a couple of more.
(27:10):
I might have to do a part twoon this because there's uh, uh,
that's not too many, that'sprobably like two left.
Uh, I just don't like to do alot.
I think sometimes if I do toomuch, uh, it's already.
You know I don't want to do toomuch and it might, it might
bore you, so I'm going to do apart two.
(27:31):
I'll do a part two on this, um,one day.
But yeah, and it's amazing thatit does all this, and what?
In a matter of seconds, right,two, three seconds it takes to
do all the stuff that I justtold you.
Right, the computer does itbefore the computer goes into,
(27:53):
you know, before you can log into Windows, right?
So it's it's pretty amazingthat it does all this stuff.
Now, um, you know, all thisthing 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, butit was a good thing to learn.
(28:15):
A lot of this stuff is on theCompti 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 listeningand I hope you learned
(28:35):
something today, especiallyabout posts until next time.
This has been a presentation ofLittle Chacha Productions.
(28:56):
Art by Joachim.
Music by Art by Sarah.
Music by Joachim.
If you want to get in contactwith me, you can.
My email address isProfessorJRotjrod at gmailcom.
I'm also at Instagram atProfessor J Rod.
And welcome to Technology Tap.
(00:29):
I'm Professor Jay Rock.
In this episode we're going totalk about post power on self
(00:56):
test.
Let's get into it All right andwelcome back everyone.
Hope everybody had a wonderful,wonderful Thanksgiving and
welcome back.
Let's finish off the rest ofthe year strong.
(01:17):
Right here is almost over 2023.
It's almost in the books.
We got about 34 days left as oftoday, November 27.
And let's finish up the yearstrong.
So, for those of you who arelistening for the first time, my
name is Professor Jay Rod and Ido these podcasts Based on the
(01:37):
comp T exams.
I go over topics, quickquestions and answers and
different stuff that comes up inthe computer world as far as it
relates to come to you and thecompany exam.
So, like, if there's a newversion of the exam coming out,
I'll talk about that.
If I get a hold of somequestions, I'll drop them here
(01:58):
in the podcast and then we goover different objectives in the
exam.
So one of the objectives of theexam is post right power off
self test.
The post is a diagnosticprocess performed by the vials
during the boot up sequence of acomputer.
The primary purpose of post isto check the integrity of
essential hardware componentsand ensure that the system is in
(02:20):
a suitable state for theoperating system to load.
And we're going to give abreakdown of the post process.
Initialization of CPU theinitialization of the CPU during
post involves preparing thecentral processing unit for
operation.
This process is assures thatthe CPU starts in a known state
and is ready to executeinstructions.
(02:41):
Here are the key steps involvedin initialization of the CPU
during post reset operation.
When the computer is powered onor or restarted, a reset signal
sends CPU.
The CPU initializes itself byresetting its external state to
a predefined starting point.
Fetching reset vector the CPUfetches the reset vector.
(03:03):
A reset vector is a memoryaddress with the initial program
counter value is stored.
The program counter is aregister in the CPU that keeps
track of the memory address ofthe next instructions to be
executed.
Setting the program counter theCPU sets the program counter
with the value fetch from thereset vector.
This determines the startingpoint in memory for the
(03:25):
execution of instructions.
Initialization of registers theCPU initializes its general
purpose registers to knownvalues.
Specific registers may be setto default values or cleared to
ensure a clean state.
Setting flags the CPU statusflags, such as zero flag, carry
the flag and overflow flags aretypically set to the default
(03:48):
values.
These flags are used toindicate the outcome of a
rhythmic and logical operations.
Mode settings depending on theCPU architecture, the process
may operate in different modes,for example real mode or
protected mode.
The CPU sets its mode toinitial state, determining how
it interacts with memory andother system components.
(04:08):
Initializing control registerscontrol registers, which
configure the various aspects ofthe CPU operations, are
initialized to default values.
These may include registersthat control memory management,
interrupt handling and othersystems level functions.
Self-test and diagnose checksthe CPU may perform self-test
(04:29):
and diagnose check duringinitialization to ensure that
internal components arefunctioning correctly.
Any errors detected duringthese checks may result in an
error message or diagnostic code.
By the end of the CPUinitialization process, the
processors, in the state way,can start executing instructions
from the system firmware orbootloader.
The overall goal is toestablish a reliable and
(04:52):
consistent starting point in theCPU operation, ensuring that
subsequent instructions areexecuted correctly as part of
the BUDO sequence.
Next we're going to talk aboutmemory testing.
Memory testing is a crucialcomponent of the Power On Self
test performed by the computerduring the BUDO process.
The purpose of the memory testis to check the integrity of the
(05:13):
system's RAM.
Random access memory RememberRAM is volatile memory that
stores data and machine codecurrently being used and
accessed by the computer'sprocessor.
Here's an overview of it.
Memory address check the poststarts by testing different
memory address to ensure thatthe RAM is accessible.
It writes specific patterns ofdata to different memory
(05:34):
locations and then reads thedata back to verify correctness.
Data bus test the data bus isthe communication pathway
between the CPU and the RAM.
The memory test checks the databus by writing data to the RAM
and then reading it back toensure that the data is
transferred correctly.
Address bus test the addressbus is responsible for
specifying a memory address.
(05:55):
The post test the address busby verifying that the CPU can
correctly address differentlocations.
In the RAM Pattern test.
The memory test often usesspecific patterns, such as all
zeros or ones alternatingpatterns to write and to read
from memory.
This helps identify issues withspecific bits or cells in the
(06:16):
memory Walking bit test.
This test involves writing aspecific bit pattern to memory
and then shifting the bitpattern to the next memory
location.
It helps detect stuck or faultybits in memory.
Checkerboard test.
The checkerboard testalternates between writing
patterns to odd and even memoryaddress.
It helps identify issues withadjacent memory locations.
(06:39):
March test March test involvesa sequence of reading and
writing operations thattransverse throughout the memory
.
Tests like March C and March Bare variations designed to
detect different type of memoryfaults.
Bit flip test the bit flip testcan intentionally flip
individual bits in memory tocheck that the memory can
correctly store and retrieve thealtered data.
(07:00):
And memory size detection thepost may also detect and verify
the amount of memory installedto ensure the system recognize
the correct memory size.
If errors are detected duringmemory tests, the post typically
generates error messages orbeep codes providing information
about the nature and thelocation of the memory issues.
(07:22):
Users or technicians can usethis information to diagnose and
address hardware problems.
A successful test is criticalto ensuring the stability and
reliability of the computersystems, as faulty RAM can lead
to a priority of issues,including system crashes, data
corruptions and unprecedentedbehavior.
(07:44):
Power supply checks A powersupply checks are essential part
of the post and overall systemdiagnostic.
Stable and reliable powersupply is critical for the
proper functioning of a computersystem.
Here are some common powersupply checks performed during
post Voltage railing monitor thepower supply unit provides
(08:06):
different voltage level,commonly 12 volt, 5 volt and 3.3
, to various components in thesystem.
The post may check the voltageof these rails to ensure that
they are within acceptabletolerance levels.
Deviation from the specificvoltage levels can indicate
power supply issues.
Power good signal the powersupply generates a power good
(08:27):
signal to indicate that allpower rails are stable and
within the specific voltagerange.
The system wait for the signalbefore proceeding with the boot
process.
The power good signal is notreceived, as system may halt to
prevent potential damage.
Overvoltage and undervoltageprotection the power supply may
have built-in protectionmechanisms to prevent
(08:48):
overvoltage or undervoltagesituations.
The post checks for overvoltageor undervoltage conditions and
takes appropriate actions tosafeguard the components.
Short circuit protection Powersupply often includes short
circuit protection to preventdamage in the event of a short
circuit in the system.
The post may check for shortcircuits and respond accordingly
.
Power supply fan check.
(09:11):
The post may check whether thefan in the power supply is
operational.
A malfunctioning fan can leadto overheating and the system
may halt or generate warnings ifthe fan is not working properly
.
Power on delay Some systemsincorporate a power on delay to
ensure that the power supplystabilizes before other
components start operating.
This delay helps prevent issuesthat could arise from unstable
(09:33):
power supply during the initialmoments of powering.
On Load test, the post mayperform load tests to check how
well the power supply handlesvarious load Fluctuation in
power.
Demand, such as the startup ofcomponents, should be handled
smoothly by the power supplyPower factor correction check.
(09:54):
Some power supplies includepower factor correction to
improve the efficiency of powerusage.
The polls may check whether thePFC is functioning properly.
If any issues are detectedduring the power supply checks,
the polls may generate errorsmessages, beep codes or other
indicators to alert users ortechnicians about possible
problems.
(10:15):
Addressing power supply issuesis crucial to ensure systems to
literally improve and damage toother components.
If you suspect power problems,it is recommended that you
consult a system documentationand seek assistance from a
technician support or aqualified technician.
Next is an initialization ofinput-output devices, and this
(10:37):
is a crucial step of post duringthe boot-up sequence of a
computer.
The IO devices includeperipherals such as keyboard,
mouse, storage devices and otherexternal devices connected to
the computer.
The initialization of thesedevices ensure they are
recognized and operational.
Here's an overview Immeratingdevices the system BIOS begins
(11:00):
by enumerating and identifyingthe IO devices connected to the
system.
This process involvesidentifying the type and the
location of each device.
Initializing system bus thesystem bus PCI, pcie that
connected the CPU to various IOdevices are initialized.
This involves configuring thebus and ensuring proper
communication between the CPUand the connected devices.
(11:23):
Assigning resources the BIOS,or UEFI, assigns system
resources, such as IRQs,interrupt requests if you don't
know what that is IO addressesand memory address to each IO
device.
This allocation ensures thatdevices can operate without
conflicting with each other.
Testing IO device the POSTperforms basic tests on each IO
(11:43):
device to ensure they arefunctioning.
For example, the system maycheck whatever keyboard and a
mouse respond to input or if thestorage device can be accessed.
Loading device drivers thesystem firmware may load basic
device drivers for the centralIO device, enabling
communication between theoperating system and these
devices.
How are you gonna use thekeyboard right?
(12:05):
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 stepto ensure that critical devices
can be accessed during the bootprocess.
Detecting bootable devices thesystems identify and prioritize
bootable devices such as harddrives, solid state drives or
optical drives.
The BIOS, or UEFI, determinesthe device from which the
(12:28):
operating system will be loaded.
Initializing mass storagedevices Mass storage devices,
such as hard drive or SSD driveundergo initialization checks to
ensure they are responsive andaccessible.
The system may check thepresence of valid boot record on
these devices.
Initializing display devicesdisplay devices such as graphic
(12:49):
cards and monitors areinitialized to enable video
output.
The system sets displayresolution and refresh rates
based on the capabilities of theconnected monitor.
Loading expansion card firmwareIf there are expansion cards in
the system, for example graphiccards, network cards, their
firmware may be loaded andinitialized.
(13:11):
This ensures that additionalfunctionality provided by these
cards is available to the system.
And then, finally, networkinitialization If the system has
integrated or add on networkinterfaces, the firmware may
initialize these interfaces.
This enables networkcommunication and it may involve
(13:31):
containing IP address throughDHCP.
So when you're obtaining an IPaddress from DHCP, this is where
it does it.
At this point, again, if anyissues are detected during
initialization of IO devices,the post may generate error
messages, because all displaydiagnostic information to
(13:53):
indicate the nature of theproper Proper initialization of
the IO devices is essential forsuccessful booting of the
operating system and the overallfunctionality of the computer
system.
Next we go to Biles integritycheck.
The integrity check is acritical step in the power on
(14:13):
self-test process during thecomputer's bootup sequence.
The Biles is a firmware thatresides on a chip on a
motherboard and it provides lowlevel control for the hardware
components on the computer.
Ensuring the integrity of theBiles is critical for the
system's stability and properfunctioning.
Here's an overview of the Bilesintegrity check.
(14:35):
Rom Reno memory check.
The BIOS is typically stored ina non-biotel memory chip, often
referred to as ROM, read-onlymemory or flash memory.
During the process, the systemchecks the integrity of the BIOS
stored in ROM.
This involves reading the BIOScode from memory and verifying
its integrity Check.
Some verification the BIOS codeis often accompanied by a
(14:58):
checksum or hash value, which isa mathematical sum calculated
based on the contents of theBIOS.
The post performs a checksumverification to ensure that the
calculated checksum matches theexpected value.
If the checksum does not match,it suggests that the BIOS code
may be corrupt or modified.
Digital signature if applicable.
(15:19):
Some modern systems may usedigital signatures to verify the
authenticity and integrity ofthe BIOS code.
A digital signature is acryptographic mechanism that
ensures that the code has notbeen tampered with.
The BIOS may contain a digitalsignature and the post checks
its validity.
Boot block integrity check theBIOS typically has a small
(15:41):
portion known as boot block thatis responsible for essential
functions, including the initialstages of the boot process.
The integrity of the boot blockis checked to ensure that
critical functions such asreading from storage devices are
intact.
Error handling If any issuesare detected during the BIOS
integrity check, the post maygenerate errors and beep codes
(16:04):
or displays informationindicating a problem.
Error messages may providedetails about the nature of the
issue, such as a checksummismatch or corrupted BIOS, and
then BIOS recovery, if it'savailable.
Some systems are equipped withBIOS recovery mechanism that can
be activated if the primaryBIOS is found to be corrupt.
(16:24):
In the event of the BIOSintegrity failure, the system
may attempt to recover using abackup copy of the BIOS or
initiated process to flash theBIOS.
Ensuring the integrity of theBIOS is critical because the
BIOS plays a fundamental role inthe early stages of the boot
process.
If the BIOS is compromised orcorrupt, it can lead to systemic
(16:45):
abilities failures or aninability to boot.
The operating systemManufacturers often provide
tools and procedures forupdating or recovering the BIOS
in case of issues, emphasizingthe importance of maintaining
BIOS integrity.
Next we're going to do expansioncards.
Expansion card checks are partof the post process that occurs
(17:07):
during computed boot up sequence.
Expansion cards are additionalhardware components such as
graphic cards, network cards,sound cards and other
peripherals that can beinstalled in expansion slots on
the motherboard.
The post verifies the presenceand functionality of these
expansion cards to ensure propersystem operation.
Here's an overview Presencedetection the post checks for
(17:31):
the presence of expansion cardsin their respective slots on the
motherboard.
It detects the type and numberof expansion cards installed.
Initialization of integratedcircuits Each expansion card
contains integrated circuitsresponsible for a specific
function.
The post initializes these ICsto ensure they're ready for
(17:52):
operation.
Testing for basic functionalitythe post performs basic tests
to ensure that each expansioncard is functioning correctly.
For example, a graphic card maybe tested for video output, a
network card for networkconnectivity or a sound card for
audio output.
Address address assignments thesystem assigns addresses,
(18:13):
interrupts and other resourcesto each expansion card.
To prevent conflicts, the postensures that these assignments
are made correctly and do notoverlap with other devices.
Rq handling or interruptrequest handling Expansion cards
often use interrupts tocommunicate with the CPU.
The post checks the RQ settingsfor each expansion card to
(18:34):
prevent conflicts and ensureproper communications.
It is very rare nowadays,ladies and gentlemen, that you
get an RQ conflict.
Back in the day it was commonEvery time you put an expansion
card in you had to worry aboutRQs, but nowadays you don't.
Expansion ROM initializationSome expansion cards have
built-in firmware or expansionROMs that provide additional
(18:56):
functionality.
The post initializes expansionROMs to make sure they're
accessible and operational.
Air detection and reporting Ifany issues are detected during
the expansion card check, thepost may generate error messages
, beep codes and displaydiagnostic information.
Error messages help identifythe specific expansion card
causing the problem.
(19:17):
Graphic card initialization theinitialization of a graphic
card is a critical part of theexpansion card check.
The post ensures that thegraphic card is operational and
capable of providing videooutput to the display.
Boodlewood deviceidentification Some expansion
cards, such as storagecontrollers, may be responsible
(19:38):
for connecting to bootabledevices, for example hard drives
.
The post identifies andverifies the presence of these
bootable devices.
Numeric interfaceinitialization If a network
interface card is present, thepost initializes it to enable
network connectivity.
This may involve obtaining anIP address through the HCP.
(19:59):
The expansion card checks areimportant for ensuring that all
components of the system areproperly detected and
initialized during the bootprocess.
Any issues identified duringthis phrase or this phase can be
critical for digusting andresolving hardware related
problems.
If there are problems withspecific expansion cards, users
(20:21):
may need to reset, take it outand put it back or replace the
card, update firmware or driversor address any conflict in the
system's configuration.
Next we're going to go with thedisplay test.
It's a little bit moreexpanding on the monitor and the
graphics card.
The display test is a criticalcomponent of post-process during
(20:42):
the computer's boot up sequence.
This test focuses on verifyingthe functionality of the display
subsystem, which includes thegraphic card, the monitor and
related components.
The primary goal is to ensurethat the system can provide a
video output to the display andthe display is capable of
presenting information to theuser.
Here's an overview.
(21:05):
Our graphic card initializationthe post begins by initializing
the graphic card, which isresponsible for rendering images
and sending them to the display.
This involves configuring thegraphics card and ensuring that
it's operational.
Checking video memory the postmay perform a quick test of the
video memory on the graphic cardto ensure that it's functioning
(21:26):
correctly.
Any issues with the videomemory can lead to graphical
artifacts or display issues.
Setting display parameters thesystem configures the display
parameters, such as screenresolution, refresh rate, based
on default settings or userdefined preferences so that in
the bios you can find output todisplay the post and signals of
display instructing it to showspecific patterns or information
(21:49):
.
This allows the systems toverify the display is receiving
signals and can presentinformation.
Color and pixel text.
The display makes sure seriesof colors, patterns or pixel
grids to ensure that each pixelon the screen is functional.
This helps identify any deadpixels or abnormalities in that
(22:09):
display.
Testing multiple monitors If youhave more than one systems will
multiple monitors may undergotests to ensure that all
connected devices arefunctioning as expected.
This includes checking forcorrected, correct detection and
configuration and multipledisplay outputs.
User interface elements somesystem display basic user
(22:30):
interface elements during thepost, such as manufacturers logo
, system information ordiagnostic message.
This provides visual feedbackto the user and indicate that
the display system isoperational.
Error messages and beep codesIf any systems are detected
during the display test, thepost may generate error messages
, beep codes and or other visualindicators to alert the users.
(22:52):
These indicators can helpdiagnose the problem with
graphical with the graphicalcards, monitor or display
connections.
External display checks.
For systems with externaldisplay connections HDMI or
display port the post may checkthe functionality of these
connectors and the correspondingsignals.
The display test is criticalbecause it can confirm that a
(23:14):
computer can communicate withthe display hardware, providing
a visual interface for the user.
If the issues are identifiedduring the test, users may need
to check the display connections, test with different monitor or
cable, or troubleshootingproblems with the graphic cards
or its drivers.
The visual feedback providedduring the display test is
(23:36):
valuable for diagnostic andresolving potential display
related issues.
Next we have and this isprobably going to be the last
one storage device.
Storage device checks are inintegral part of post process
during the computer boot upsequence.
These checks are designed toverify the presence, integrity
(23:59):
and functionality of storeddevices, such as hard drive,
solid state drives and otherstorage peripherals.
Here's the overview of thestorage devices check during
post detecting attached storagethe post begins by detecting and
identifying the storage deviceconnected to the system.
This includes internal drives,external drives and other
(24:19):
storage peripherals.
Initialization of storagecontrollers the storage
controllers, which manage datatransfer between storage devices
and the rest of the systems,are initialized.
This involves checking theintegrity of the controller and
ensuring it is ready tocommunicate with the attached
storage devices.
Checking storage device powerand connection the post verifies
(24:40):
that the power supply and dataconnections to the storage
device are stable and correctlyconfigured.
Loose cables or power issuescan lead to storage device
failures.
Smart self monitoring, analysisand reporting technology checks
If supported by the storagedevice, the post may query smart
data to assess the help of thedrives.
(25:02):
Smart checks can identifypotential issues with the drives
, such as bad sectors orimminent drive failure.
Bios UEFI recognition the postensures that the system bios or
UEFI recognizes storage device.
The bios UEFI providesinformation about the connected
drives and their basicconfigurations.
(25:22):
Boot sector and partitionchecks the post checks the boot
sector and partition informationof bootable drives to ensure
that they are correctlyconfigured.
If the system is configured toboot from a specific drive, the
post verifies that the drivecontains a valid boot loader.
Read write test Basic read andwrite test may be performed on
(25:42):
the storage device to ensurethat data can be properly
written to and read from devices.
These tests help identifyissues with data integrity and
storage device.
Raid configuration checks ifapplicable.
In a system with a RAID, whichis redundant array of
independent disk configurations,the post verifies the status
(26:05):
and the integrity of the RAIDarrays.
This includes checking for faildrives and ensuring that the
RAID configuration is consistent.
Error handling If any issuesare detected during the storage
device check, the post maygenerate error messages because
of display diagnosticinformation.
These indicators help identifythe nature of the storage
(26:29):
related problem, Loading storagedevice data if needed.
If specific storage devices arerequired for proper operation,
the post may load these devicesto enable connections between
the operating system and thestorage device.
Ensuring the proper functioningof storage devices is critical
(26:49):
for the successful booting ofthe operating system and the
overall stability.
If the storage device issuesare identified during the post,
users may need to check cables,replace faulty drives, update
firmware or addressconfiguration problems to ensure
reliable storage performance.
Now there is a couple of more.
(27:10):
I might have to do a part twoon this because there's uh, uh,
that's not too many, that'sprobably like two left.
Uh, I just don't like to do alot.
I think sometimes if I do toomuch, uh, it's already.
You know I don't want to do toomuch and it might, it might
bore you, so I'm going to do apart two.
(27:31):
I'll do a part two on this, um,one day.
But yeah, and it's amazing thatit does all this, and what?
In a matter of seconds, right,two, three seconds it takes to
do all the stuff that I justtold you.
Right, the computer does itbefore the computer goes into,
(27:53):
you know, before you can log into Windows, right?
So it's it's pretty amazingthat it does all this stuff.
Now, um, you know, all thisthing 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, butit was a good thing to learn.
(28:15):
A lot of this stuff is on theCompti 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 listeningand I hope you learned
(28:35):
something today, especiallyabout posts until next time.
This has been a presentation ofLittle Chacha Productions.
(28:56):
Art by Joachim.
Music by Art by Sarah.
Music by Joachim.
If you want to get in contactwith me, you can.
My email address isProfessorJRotjrod at gmailcom.
I'm also at Instagram atProfessor J Rod.
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