[SBE] Rack standards

[Smith, Jeff]

Right from Wikipedia...

 

http://en.wikipedia.org/wiki/19-inch_rack

 


Overview and history


Equipment designed to be placed in a rack is typically described as
rack-mount, rack-mount instrument, a rack mounted system, a rack mount
chassis, subrack, rack mountable, or occasionally simply shelf. The
height of the electronic modules is also standardized as multiples of
1.75 inches (44.5 mm) or one rack unit
<http://en.wikipedia.org/wiki/Rack_unit>  or U (less commonly RU).

Because of their origin as mounting systems for railroad signaling
<http://en.wikipedia.org/wiki/Railroad_signaling>  relays
<http://en.wikipedia.org/wiki/Relay> , they are still sometimes called
relay racks, but the 19-inch rack format has remained a constant while
the technology that is mounted within it has changed to completely
different fields. The 19-inch (482.6 mm) standard rack arrangement is
widely used throughout the telecommunication
<http://en.wikipedia.org/wiki/Telecommunication> , computing
<http://en.wikipedia.org/wiki/Computer> , audio
<http://en.wikipedia.org/wiki/Sound_recording_and_reproduction> ,
entertainment <http://en.wikipedia.org/wiki/Entertainment>  and other
industries, though the Western Electric
<http://en.wikipedia.org/wiki/Western_Electric>  23-inch standard
<http://en.wikipedia.org/wiki/23-inch_rack> , with holes on 1-inch (25.4
mm) centers, prevails in telecommunications.

19-inch racks are often used to house professional audio and video
equipment, including amplifiers <http://en.wikipedia.org/wiki/Amplifier>
, effects units <http://en.wikipedia.org/wiki/Effects_unit> ,
interfaces, headphone <http://en.wikipedia.org/wiki/Headphone>
amplifiers, and even small scale audio mixers. They are also widely used
for computer server <http://en.wikipedia.org/wiki/Computer_server>
equipment, allowing for dense hardware configurations without occupying
excessive floorspace or requiring shelving. A third common use for
rack-mounted equipment is industrial power, control, and automation
hardware.

Typically, a piece of equipment being installed has a front panel height
1/32-inch (0.031 inches (0.787 mm)) less than the allotted number of Us.
Thus, a 1U rackmount computer is not 1.75 inches (44.5 mm) tall but is
1.719 inches (43.7 mm) tall. 2U would be 3.469 inches (88.1 mm) instead
of 3.5 inches (88.9 mm). This gap allows a bit of room above and below
an installed piece of equipment so it may be removed without binding on
the adjacent equipment.

In 1965 a durable fiber reinforced plastic
<http://en.wikipedia.org/wiki/Fiber_reinforced_plastic>  19-inch
rackmount case was patented by ECS Composites and became widely used in
military and commercial applications for electronic deployment and
operation. State-of-the-art rackmount cases are now also constructed of
thermo stamped composite, carbon fiber
<http://en.wikipedia.org/wiki/Carbon_fiber>  and DuPont
<http://en.wikipedia.org/wiki/DuPont> 's Kevlar
<http://en.wikipedia.org/wiki/Kevlar>  for demanding military and
commercial uses

 

 

Jeff Smith CSRE CBNT

Supervisor Broadcast Systems

Clear Channel Radio NYC

Power 105.1, 103.5 WKTU, Z100, 106.7 Lite FM, Q 104.3

 

From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of Dan
Rapak
Sent: Tuesday, October 25, 2011 1:53 PM
To: SBE Broadcast Group
Subject: [SBE] Rack standards

 

I just received a question from a colleague that made me scratch my
head. Where did the standards for equipment racks (rack units, 19"
width, hole spacing) come from and why were they set at these values?

 

Dan Rapak

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