Joe put forth on 1/14/2010 4:57 PM: > Stan Hoeppner wrote: >> Boyd Stephen Smith Jr. put forth on 1/14/2010 12:13 PM: > >> >>> [2] I usually estimate that a "U" is about 1.5 in. or 37.5 mm. >> >> Your estimation is wrong. One EIA/TIA Rack Unit, or "U", is exactly >> 1.75". It >> was defined in standard EIA-310-D in 1992, has been with us for 18 >> years now. >> There shouldn't have to be any guess work or "estimating" involved >> here. ;) >> > > That's probably one of the more recent standards, but the 19 inch rack > has been around for close to a century, having started life in the > telephone business. More than thirty years ago, I was working on > 1946-designed 19 inch rack gear.
19" width racks do predate EIA-310-D by many years. This standard merely formalized the 19" width for electronic and telecommunications use. The key standard that was established in 1992 though was a equipment "height" and mounting hole placement, so that one could assemble a rack full of gear from different manufacturers without having gaps between equipment, or running into "overlap" issues when installing two dissimilar pieces of gear one atop the other. Historically, telecom frames have been 24" not 19", and they are called "frames" in the telco industry, not "racks". 19" racks didn't start appearing in telco central offices until the mid-late 1990s with the explosion of the internet and telcos becoming defacto ISPs in many markets, especially after the advent of DSL. One could/can track this trend merely by watching the available "rack" form factors of SUNs Netra and standard data center servers. In the early days SUN offered 24" wide form factor Netra servers. Now it's all 19" because such racks now proliferate in Telco COs, whereas beyond 15 years ago it was all 24". SUN no longer offers 24" frame rackmount servers, although their StarFire series (e10K-e25K) used a 24" wide custom full height cabinet. Their current flagship Sparc server comes in a 33.5" wide cabinet. -- Stan -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
