What exactly is POST function?

Discussion in 'General Gaming Discussion' started by brickmii82, Jun 19, 2016.

  1. brickmii82

    brickmii82 GBAtemp Advanced Fan

    Feb 21, 2015
    United States
    So I've been doing RGH's, Letterbomb, a PS3 here and there, and I've seen POST or Post pop up quite a few times. I know it stands for Power On System Test, and have a general idea of what it is. Could anyone possibly give me a slightly detailed explanation of how it functions, what it generally consists of, and/or the variations utilized in its application/procedure?
  2. FAST6191

    FAST6191 Techromancer

    pip Reporter
    Nov 21, 2005
    United Kingdom
    I don't know where you would have seen that pop up in such discussions, I guess I have seen it a few times but it seems an odd thing to pick up on.

    Anyway on what system? It varies quite considerably, even within the PC world (the tests for a server can be rather more involved than a desktop set to try to boot as far as possible).

    Generally computers will have various types of memory, and different means of speaking to devices that are not the CPU and memory. Basic POST stuff is usually testing this memory, seeing if devices are there or devices have changed since last boot. The extent of memory testing usually being the main change here -- you can test CPU registers and various levels of cache almost instantly, system memory takes longer so most consumer stuff will skip it unless it has changed but servers not so much and a full hard drive scan can take hours so most will skip that, unless it is a server that lost power*, exceptions for full hard drive scans tending to come if you instead have a small ROM or CF card or something that the device boots from or wants to ensure security for and will then test. Some POST stuff might also set a reference value for limits -- if the RAM errors out past 800Mhz then it will lock it down to the last working value, another device might go faster and thus gain a high cap on a given value. Equally other things might have onboard diagnostics (SMART in hard drives being a good example).

    *unexpectedly losing power to your server is a very bad thing indeed, and not doing a full drive scan or pressing the button to skip checks as it comes back up would probably get you fired in a lot of places.

    Here is a flow chart of an Oracle setup

    For the most part though it is just something I have to know what it is (like boot sectors) rather than the long lists of boring specifics. I would not suggest going into those boring specifics for the PC, however what I would suggest looking at which is somewhat related is secure embedded electronics, fault tolerant embedded electronics and high availability embedded electronics as all of those often make fairly extensive use of self checking and self testing, and also feeds pretty directly into hacking devices as well.
    brickmii82 likes this.
  3. osaeed09

    osaeed09 Member

    Jul 17, 2008
    United States
    Fast6191 is right. That's basically the definition. But here explains it in a different way

    When power is turned on, POST (Power-On Self-Test) is the diagnostic testing sequence that a computer's basic input/output system (or "starting program") runs to determine if the computer keyboard, random access memory, disk drives, and other hardware are working correctly.

    If the necessary hardware is detected and found to be operating properly, the computer begins to boot. If the hardware is not detected or is found not to be operating properly, the BIOS issues an error message which may be text on the display screen and/or a series of coded beeps, depending on the nature of the problem. Since POST runs before the computer's video card is activated, it may not be possible to progress to the display screen. The pattern of beeps may be a variable numbers of short beeps or a mixture of long and short beeps, depending on what type of BIOS is installed.

    The patterns of beeps contain messages about the nature of the problem detected. For example, if the keyboard is not detected, a particular pattern of beeps will inform you of that fact. An error found in the POST is usually fatal (that is, it causes current program to stop running) and will halt the boot process, since the hardware checked is absolutely essential for the computer's functions. Source- http://whatis.techtarget.com/definition/POST-Power-On-Self-Test
    brickmii82 likes this.