Blog 2 Assignment POST

I have selected the POST and ESD items from our list. Please drink lots of coffee before viewing.

Power On Self Test better known as POST, is the first sequence in the pre-boot routine. This self test program is run from the BIOS and verifies, through diagnostics, that all the systems in the computer are functioning properly. If a system passes POST depending on the type of system, you will hear one or two beeps as the boot program continues to run.
On a hard boot, the first system checked is the power supply. This check verifies the correct voltages are present by way of the power good signal. Some systems use a reset instead of a power good signal. Either way, the condition of this signal tells the system to continue or hold. The next check is the BIOS itself. It must report a valid checksum to indicate that it does not contain corrupt data. From here, different systems may alter the following sequence but the checks must all be done.
The CPU must indicate that it has completed its power on reset and is capable of initializing communications with memory. Read and write tests are done to the first 64KB to verify bus, module and controller function. The CMOS must also pass a checksum test to insure there is no corrupt data. The last series of tests check the I/O functions are working properly including the video. Again, a series of read and write operations are preformed.
The soft boot routines are not quite so extensive. Much of the information from the hard boot are saved and do not need to be re-run. After for POST has run the operating system takes control and finished initializing the hardware with the installed device drivers.
I won't bore you with each beep code and description since they will be different depending on the type of BIOS driving the system. They will show the obvious errors such as BIOS and CMOS checksum errors and some not-so-obvious errors like errors with the system clock, PCI bus communications errors, coprocessor erros and configuration errors. I have seen these errors personally and wouldn't wish them on any repair technician.
POST does not perform all the startup routines though. During startup, it may pass the initialization of certain devices off to other programs. In summary, the POST is not only a necessity for the computer to become operational, but is also the best tool you can use to troubleshoot a system.