[GTALUG] New Deaktop PC -- To Run debian Linux - PCPartPicker Recipe;

D. Hugh Redelmeier hugh at mimosa.com
Wed Mar 28 15:04:43 EDT 2018


| From: Lennart Sorensen via talk <talk at gtalug.org>

| On Wed, Mar 28, 2018 at 09:50:42AM -0400, Steve Petrie, P.Eng. via talk wrote:
| > *** I know that PS/2 is an ancient interface. I only chose PS/2 because it is my understanding that a PS/2 keyboard and mouse combination is better supported and earlier, during the actual Linux boot process, than a USB keyboard and mouse combination. So PS/2 keyboard and mouse offer more liklihood of functionality when there are Linux boot problems.
| 
| The BIOS emulates PS/2 for USB mouse/keyboard just fine and should
| not cause any issues.  But yes it is slightly more complex to use a
| USB device.  I don't remember the last time I dealt with a PS/2 device.
| I don't miss them.  I don't think I have had a problem with a USB keyboard
| for a decade.  USB mice are never a problem since you never need a mouse
| unless the system is actually booted normally, so only for a keyboard is
| PS/2 at all interesting.  Well unless you are one of those extreme gamers
| that care about the potentially lower latency of PS/2 mice over USB mice.

(I may have some of this wrong.  These details are considered too
complicated to explain to users so we are just supposed to assume
everything just works.)

- firmware isn't BIOS these days.  In fact, that was a misnomer on the
  PC since day 1.  It's a carry over from the CP/M days on Intel 8080
  processors.  Now it is called, uhh, firmware.  Or UEFI firmware.

- UEFI firmware usually (but not always) includes a CSM (Compatibility
  Support Module) to emulate BIOS for the sake of old OSes.  If
  present in the firmware, it usually can be enabled or disabled in
  the firmware config menus.  As far as I know, all stand-alone
  motherboards have a CSM (Win 10 tablets often do not).

- System Management Mode is a little known feature of all Intel and
  AMD x86 processors since the 486 and the Am486 25 years ago.  It
  allows the firmware to keep some control after booting the OS.  The
  OS has no control over this.

- SMM is used (among other things) to capture USB keyboard and mouse
  events and turn them into simulated PS/2 events.  This is usually
  optional but default behaviour on motherboards.  In effect, this
  emulation appears to be a hardware feature.

- One other limitation of USB and not PS/2 is that there is a limit to
  how many keys can be pressed at once (n-key rollover) and sensed
  properly.  The limit is based on how many key events can be recorded
  in a single USB packet.  But the limit is something like 6.  Surely
  more than enough.

So: mouse emulation and BIOS emulation are behind the back of the OS.
This means legacy OSes should have no trouble with these features.

I recommend using a USB keyboard and mouse.  Unless you are a crazy gamer.


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