[ale] No RAM = No BIOS?

[alan at alanlee.org]

On August 15, 2012 at 5:40 PM "mike at trausch.us" <mike at trausch.us> wrote:

> On 08/15/2012 04:37 PM, JD wrote:
> > Anyone seen a PC not get to the BIOS screen just because RAM isn't
> > installed?
> > There isn't a troubleshooting section in the MB manual. No beeps at boot
> > either.
>
> BIOS cannot work without RAM.  Simple as that.
>



Sure it can. Processors start by initializing the program counter with a set
reset vector address.  They fetch the first instruction at that program counter
address.  They then execute it and increment the program counter.  It's kinda
how computers work in general.  You only need RAM to store data (i.e.
variables).  As long as you don't need any persistent storage, you can execute
in place directly out of ROM all day long.  All processors do this for a BIST
(Built-in Self Test) or POST (Power on Self Test) including configuring the
basic system clock tree, reading the EEPROMs on the installed DIMMs via I2C to
determine RAM timings and voltage requirements, and programming the Power
Management ICs (PMICs) to provide those correct voltages and setting the PLLs to
provide the required clocks so the SDRAM will even work.  Most SoCs today
include some small amount of on-die SRAM just for BIOS/startup code; including
some Intel processors.





> You *should* be getting some form of beeping, but if there's no speaker> in
> the computer...
>
>         --- Mike



What do you think provides the beeping?  (BIOS!)

-Alan

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