Editing Digital Equipment Corporation (section)

=== Digital modules (1958) ===
[[File:Dec SYSTEM BUILDING BLOCKS 1103.jpg|thumb|System Building Blocks (System Module) 1103 hex-inverter card (both sides)]]
[[File:PDP-1 System Building Block No. 4106.jpg|thumb|PDP-1 System Building Block #4106, circa 1963 - note that one transistor (yellow) has been replaced]]

In early 1958, DEC shipped its first products, the "Digital Laboratory Module" line. The Modules consisted of a number of individual electronic components and [[Bipolar junction transistor#Germanium transistors|germanium transistors]] mounted to a [[circuit board]], the actual circuits being based on those from the TX-2.<ref name="modules">{{cite book|first1=Richard|last1=Best|first2=Russell|last2=Doane|first3=John|last3=McNamara|chapter-url=http://research.microsoft.com/en-us/um/people/gbell/computer_engineering/00000125.htm|chapter=Digital Modules, The Basis for Computers|url=http://bitsavers.org/pdf/dec/_Books/Bell-ComputerEngineering.pdf |archive-url=https://web.archive.org/web/20100312072729/http://www.bitsavers.org/pdf/dec/_Books/Bell-ComputerEngineering.pdf |archive-date=2010-03-12 |url-status=live|title=Computer Engineering, A DEC view of hardware systems design|publisher=Digital Press|date=1978}}</ref>

The Laboratory Modules were packaged in an extruded aluminum housing,<ref>{{cite web |url=http://www.computerhistory.org/collections/accession/102633142 |title=DEC Laboratory Module&nbsp;– FLIP-FLOP 201 |website=Computer History Museum|date=1960 }}</ref> intended to sit on an engineer's workbench, although a [[19-inch rack|rack-mount]] bay was sold that held nine laboratory modules.<ref name="BuildingBlock1960">{{cite book|url=http://ed-thelen.org/comp-hist/DECbuildingBlockLogic2ndEd.pdf |archive-url=https://web.archive.org/web/20130702192719/http://ed-thelen.org/comp-hist/DECbuildingBlockLogic2ndEd.pdf |archive-date=2013-07-02 |url-status=live|title=DEC Building Block Logic|edition=Second|publisher=Digital Equipment Corporation|date=November 1960}}</ref> They were then connected together using [[4 mm plug|banana plug]] [[patch cord]]s inserted at the front of the modules. Three versions were offered, running at 5&nbsp;MHz (1957), 500&nbsp;kHz (1959), or 10&nbsp;MHz (1960).<ref name="modules" /> The Modules proved to be in high demand by other computer companies, who used them to build equipment to test their own systems. Despite the recession of the late 1950s, the company sold $94,000 worth of these modules during 1958 alone ({{Inflation|US|94000|1958|r=-2|fmt=eq}}), turning a profit at the end of its first year.<ref name=companyhistory/>{{dead link|date=February 2020}}{{better source needed|date=February 2020}}

The original Laboratory Modules were soon supplemented with the "Digital [[System Module]]" line, which were identical internally but packaged differently. The Systems Modules were designed with all of the connections at the back of the module using 22-pin [[Amphenol]] connectors, and were attached to each other by plugging them into a backplane that could be mounted in a [[19-inch rack]]. The backplanes allowed 25 modules in a single 5-1/4&nbsp;inch section of rack, and allowed the high densities needed to build a computer.<ref name=modules/>

The original laboratory and system module lines were offered in 500 kilocycle, 5 megacycle and 10 megacycle versions. In all cases, the supply voltages were -15 and +10 volts, with logic levels of -3 volts (passive pull-down) and 0 volts (active pull-up).<ref name="BuildingBlock1960" />

DEC used the System Modules to build their "Memory Test" machine for testing core memory systems, selling about 50 of these pre-packaged units over the next eight years.<ref name="present3">''Present'' 1978, pg. 3</ref> The [[PDP-1]] and [[LINC]] computers were also built using System Modules (see below).

Modules were part of DEC's product line into the 1970s, although they went through several evolutions during this time as technology changed. The same circuits were then packaged as the first "R" (red) series "[[Flip-Chip module|Flip-Chip]]" modules. Later, other Flip-Chip module series provided additional speed, much higher logic density, and industrial I/O capabilities.<ref name=present10/> DEC published extensive data about the modules in free catalogs that became very popular.