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2        $seiten_id = 'lgp30';
3        $version = '$Id: elektro-mechanik.php 688 2014-11-15 09:18:06Z heribert $';
4        $titel = 'Schoppe & Faeser: LGP 30';
6        require "../../lib/technikum29.php";
9<h2 id="lgp30">LGP 30</h2>
11The 1st-generation dataprocessing system LGP-30 was developed in the United
12States by <b>L</b>ibrascope and <b>G</b>eneral-<b>P</b>recision in the mid-1950s. About 40 such
13machines were built under a license agreement by Schoppe & Faeser in Germany.
14The LGP-30 was intended as a scientific computer system and was superseded
15by the <a class="go" href="/en/computer/early-computers.php"> <b>LGP-21</b></a> in 1962.<br>
17Programs and data are stored on 1" paper tape which are fed to a high-speed
18punch/reader. Manual input and output is performed by a so-called
19"Flexowriter" made by Friden. This device is basically an electric
20typewriter with a paper tape attachment.</p><br>
22<div class="center">
23                <img src="/shared/photos/rechnertechnik/lgp30-1.jpg" alt="LGP 30" width="850" height="380" />
24                <p class="center">     
25                <b>LGP-30 vacuum tube based computer - prior to restauration</b>
26                </p></div>
28<p>Unfortunately, our machine is missing the special interconnect cables
29for the high-speed paper tape system and the Flexowriter. Therefore we
30are looking desperately for the required <a class="go" href="/en/wanted.php#connector" target="_blank">special connectors </a>. <br>
31Apart from this, the machine is in rather good shape. First
32of all the side panels have to be repainted and all the mechanic parts
33have to be brought back to working condition. After that the electronics
34can be debugged - a true adventure, digging deep into vacuum tube based
35digital electronics.</p>
38        <div style="width: 350px;" class="desc-left borderless no-copyright">
39    <a class="popup" href="/shared/photos/rechnertechnik/lgp30-2.jpg">
40                <img src="/shared/photos/rechnertechnik/lgp30-2.jpg" alt="Front View" height="266" width="350"></a>     
41                <div class="bildtext"> 
42                        <p><b>Front View without casing</b></p> <a class="popup" href="/shared/photos/rechnertechnik/lgp30-2.jpg"> enlarge picture</a>
43                </div></div>   
45                <div style="width: 350px;" class="desc-right borderless no-copyright">
46    <a class="popup" href="/shared/photos/rechnertechnik/lgp30-3.jpg">
47                <img src="/shared/photos/rechnertechnik/lgp30-3.jpg" alt="Backside" height="262" width="350"></a>       
48                <div class="bildtext"> 
49                        <p><b>Backside without casing</b></p> <a class="popup" href="/shared/photos/rechnertechnik/lgp30-3.jpg"> enlarge picture</a>
50                </div></div>   
52<p class="clear">The technical data is rather interesting: The magnetic drum rotates at
533600 RPM, the distance between two adjacent tracks is 2mm, a single track
54has a width of 1mm and the spacing between read/write heads and the
55drum surface is 25 um! The memory capacity is pretty large for its time
56at 4,096 words of 32 bits each. The basic clock frequency is 120 kHz and
57the access time is between 2 ms and 15 ms. A single addition takes
580.23 ms while a multiplication requires 15 ms (without the necessary
59access times to the drum).<br>
60All in all, there are 113 long-life vacuum tubes and 1450 Germanium
61diodes packaged in 34 modules (12 different module types). <br>
63The paper tape reads is capable of reading 200 characters/s, the high-speed
64punch can punch at 50 characters/s while the Flexowriter is capable of
65printing 10 characters/s. <br>
67The processing unit (without peripherals) weights 350 kg.</p>
70<p class="clear">Some historical data regarding our machine: Its whereabouts prior to 1962
71are unknown. It was then used from 1962 until 1980 at a land surveying
72office for various purposes including the generation of control paper
73tapes for a ZUSE Graphomat Z64 plotter, recalculation of historic
74triangulation nets, affine transformations, Helmert-transformations,
75basic tasks for land surveying etc.<br>
77Those tasks were quite demanding and even a rather simple fit through
78three points determined by triangulation took about 3 to 4 minutes of
79computer time.<br><br>
82<div class="desc-right borderless">
83<a href="/shared/photos/rechnertechnik/lgp-trommelspeicher.jpg" target="_blank">
84                <img src="/shared/photos/rechnertechnik/lgp-trommelspeicher.jpg" alt="Trommelspeicher" height="325" width="420"></a>   
85                <div class="bildtext"> 
86                        <p>LGP-30 Magnetic Drum. The magnetic layer has some defects. <br> The photo can be enlarge.</p> 
87                </div>  </div>
89<div id="trommel"></div>
91<p>Now the restoration of this vaccum tube based computer started. The biggest
92problem is the magnetic drum memory. Currently four options are under
951. Applying a new magnetic coating to the damaged drum. This approach would
96be ideal but also the most complex solution.<br>
982. Simulating the complete drum assembly by a modern microcontroller.
99Attaching this to the vacuum tube electronics would be feasible by means of
100level shifters (0V and -20V are required for operation).<br>
1023. A discrete approach emplying RAMs, EPROMs, operational amplifiers and lots
103of glue logic. This does not have any advantages over approach 2.<br>
1054. Replacing the rotating drum by a fixed assembly holding magnetic
106read/write heads, one for each head of the drum. This approach has been
107abandoned due to its complexity.<br><br>
109Compared with the complexity of emulating the drum assembly, the missing
110cables are only a minor problem. Fortunately four experts will support the
111restoration effort. We would especially like to thank Mr. Klemens Krause
112<a href=""target="_blank">Computermuseum-Stuttgart</a>.
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