Editing Diode–transistor logic (section)

===Discrete===
The [[IBM 1401#Hardware implementation|IBM 1401]] (announced in 1959<ref>[http://www.computermuseum.li/Testpage/IBM-1401.htm computermuseum.li]</ref>) used DTL circuits similar to the circuit shown in the first picture.<ref>The IBM 1401 may have also used a current mode logic.</ref> IBM called the logic "complemented transistor diode logic" (CTDL).<ref>{{Harvnb|IBM|1960|p=6}}</ref> CTDL avoided the level shifting stage (R3 and R4) by alternating NPN and PNP based gates operating on different power supply voltages. NPN based circuits used +6V and -6V and the transistor switched at close to -6V, PNP based circuits used 0V and -12V and the transistor switched at close to 0V. Thus for example a NPN gate driven by a PNP gate would see the threshold voltage of -6V in the middle of the range of 0V to -12V. Similarly for the PNP gate switching at 0V driven by a range of 6V to -6V. The 1401 used [[germanium]] transistors and diodes in its basic gates.<ref name="IBM-1401"/>  The 1401 also added an inductor in series with R2.<ref name="IBM-1401">[http://www.bitsavers.org/pdf/ibm/140x/1401_CE_Drws_1962.pdf IBM 1401 logic] {{webarchive|url=https://web.archive.org/web/20100809033255/http://www.bitsavers.org/pdf/ibm/140x/1401_CE_Drws_1962.pdf |date=2010-08-09 }} Retrieved on 2009-06-28.</ref><ref name="Form 223-688">{{cite book |author=IBM |year=1960 |title=Customer Engineering Manual of Instruction: Transistor Component Circuits |publisher = IBM |id=Form 223-688 (5M-11R-156) |url=http://ibm-1401.info/Form223-6889-TransistorComponentCircuits.pdf |access-date=2012-04-24 }}</ref> The physical packaging used the [[IBM Standard Modular System]].