Rack computers in a nutshell
The 19”rack chassis format has been around for nearly a century, with the form factor standard rack as we know it today being introduced by AT&T in the early 1920’s for their telephony and telecommunication systems, designed to save space and allow their equipment to be flexibly mounted.
The first industrial rack-mount computer was released in 1985 by IBM and this was a passive backplane system using a full size ISA based 8088 single board computer, with built in memory, storage, power and MS DOS. This system allowed expansion for five additional ISA cards allowing the system to be specified to the customers requirement using any number of I/O and comms boards, many of them being proprietary.
Rack computer chassis use what are called “rack-units”, each being 1.75mm high so for instance a 4U rack chassis is 7 inches in height (4 x 1.75”) whilst a 2U rack is 3.5” high. These standardised units means that chassis’ along with 19” peripheral equipment can be mixed and matched in a full 19” rack cabinet, many offering up to 48U in overall height. Mounting of rack chassis in a cabinet is done using slide rails should the chassis need to be pulled out, or statically mounted used mounting brackets at the front and rear of the chassis.
19” x86 rack computer chassis are made from high grade steel or aluminium, normally with a front lockable door, behind which is access to the system fans, filters and drive bays. Additional features normally include LEDs for power, temperature and other system management functions plus ports for connecting peripherals into the system via USB, serial and even PS/2. On the rear of the chassis is where the connectivity to the main board and expansion slots are found. Traditionally industrial rack-mount computers use motherboards or a combination of backplane and single board computer (SBC) all of which are designed to fit in to a standard 19” chassis. Backplane and SBC based systems are still used when many more additional cards are needed than can be offered on an industrial motherboard with up to 20 slots available in some 6U based chassis systems. All the I/O ports required can then be fed out on to the rear of the chassis for easy connectivity in the cabinet. These ports can be a combination of main board I/O connectors like USB, serial, display etc… as well as add-on cards fitted in to ISA, PCI and PCI Express slots, offering more specialist connectivity like analog/digital I/O as well as multi-port serial and Ethernet interfaces. This design gives true versatility for the user depending on their application requirements which is why rack computers are heavily used in test, measurement and control applications. With many components and boards being fitted inside the rack system, careful and considered cabling of the system internally is essential in order to maximise airflow between the front fans which often bring in cooling air, and the rear fans which extract warmer air from out of the chassis ensuring the internal temperature in the system is kept to minimum improving system performance and reliability.
In addition to the rack computer there are now many rack-mountable peripherals and devices which all use the 19” form factor, these include rack LCD monitors, KVM drawers, UPS’, signal conditioning and DAQ systems and allows engineers to fully delivery an all-in-one rack cabinet to their exact application requirements. Such examples where rack computing technology is used in the industrial computing sector include automotive test beds, flight simulator systems, rolling stock and trackside rail control and power substation monitoring.