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DADDY BOB'S COMPUTER Q & A
October 28,
2007
Q.
On my keyboard there is a key called "Print
Scrn/SysRq. When pressed it doesn't appear
to do anything. What is its purpose?
Print
Scrn is a key present on most computer
keyboards, usually located just to the left
of the Scroll Lock key. Under earlier
command-line based operating systems like
MS-DOS, this captured what was currently
being displayed on the screen and sent it to
LPT1, which was where the default printer
was connected. In actually, it printed
whatever was on the screen hence the name
Print Scrn.
When
newer operating systems came along with
graphical user interfaces, like Windows, its
action was changed. Now it just copies what
is displayed on the screen and stores it in
the "clipboard". The clipboard is a section
of memory set aside to hold these images.
From the clipboard, it can be pasted into
any document or application that allows
pasting, and can handle graphics. The name
probably should have been changed from Print Scrn to Capture Scrn.
In
Microsoft Windows, pressing Print Scrn key
will capture the entire screen, while
pressing the alt key in combination with
Print Scrn will capture the currently
selected window. Pressing print scrn, the
alt key, and the shift key at the same time
turns on a high contrast mode.
In
versions of Windows before Windows 95, there
was easy user access to the clipboard so its
contents could be viewed. Since Windows 95,
the clipboard still exists, but it is no
longer made easy to be viewed. However, it
can still be opened but takes a little more
effort.
Click
Start, then Run, and enter clipbrd and click
OK. That will open the clipbook viewer,
which is really the clipboard and you can
see what it contains. Unfortunately, the
clipboard can hold only one image, so when
you press the Print Scrn key, whatever was
in the clipbook will be replaced.
I have
not yet found a way to open the clipboard
for viewing in Vista as it is installed by
default. But, if you copy the "clipbrd.exe"
file from XP to Vista it appears to work
just fine there.
SysRq,
short for System Request, is entered by
pressing the Shift key and the Print Scrn
key. This key can be traced back to
the operator interrupt key used on early IBM
console keyboards.
Under
MS-DOS, if a program experienced a problem
it could cause the computer to freeze up.
Some third-party TSRs (Terminate and Stay
Resident programs) were written to allow the
SysRq key to act like a panic button. When
pressed, this could (was supposed to)
terminate the hung up program and return the
computer to the DOS prompt. From
experience I can tell you that this rarely
ever worked.
Windows
NT made this key press semi-usefully if
programmed to do so, but under today's
operating systems of XP and Vista, SysRq really
doesn't do anything. |
