{"id":5935,"date":"2023-02-18T09:51:44","date_gmt":"2023-02-18T14:51:44","guid":{"rendered":"https:\/\/forths.com\/?p=5935"},"modified":"2023-02-19T11:43:24","modified_gmt":"2023-02-19T16:43:24","slug":"built-a-1975-era-computer-sort-of","status":"publish","type":"post","link":"https:\/\/forths.com\/index.php\/2023\/02\/18\/built-a-1975-era-computer-sort-of\/","title":{"rendered":"Built a 1975-era Computer (sort of)"},"content":{"rendered":"\n

In late 1974 I was fortunate enough to get some experience using an HP-2000F minicomputer with a teletype terminal in my school. Compared to using a computer today, the teletype was noisy and slow, and seemed to self-destruct every few weeks, needing repairs or adjustments to keep it printing clearly. Still, the experience seemed magical to me. A friend and I would play various games, including a Star Trek game that was purely text-based, but kept us engaged for hours as the teletype slowly printed the outcome of every Klingon battle.<\/p>\n\n\n\n

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Teletype Model 33<\/figcaption><\/figure>\n\n\n\n

I didn’t realize it then, but this was during the rise of the “minicomputer”. Minicomputers were smaller than the room-sized mainframes and cost much less, but were still the size of a refrigerator or two. Minicomputers were made by several companies including IBM, Digital Equipment Corporation (DEC), Prime, Wang, Data General, and many more. Corporate departments, mid-sized companies, and universities all found uses for the cost-effective minicomputers. In 1983, my employer’s financial systems ran on a DEC PDP11. I programmed using the DIBOL language to create sales or financial reports.<\/p>\n\n\n\n

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DEC PDP11\/70 Minicomputer<\/figcaption><\/figure>\n<\/figure>\n\n\n\n

Fast-forward to modern times, when I stumbled upon information on the internet about a fellow in Switzerland who sells 6:10 scale reproduction kits of the Digital PDP-11\/70 front panel, complete with a row of 1970s-era red and magenta switches and the requisite “blinkenlights<\/a>” flashing away. The kit runs hardware emulation on an embedded Raspberry Pi computer. This was perfect, since I had an unused Raspberry PI in my stock of spare parts. The kits are built to order, so I ordered one. The kit arrived a few weeks later.<\/p>\n\n\n\n

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Bags of parts and the circuit board<\/figcaption><\/figure>\n\n\n\n
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Parts are sorted and prepared<\/figcaption><\/figure>\n\n\n\n
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Diodes are soldered in place<\/figcaption><\/figure>\n\n\n\n
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Board is ready for testing<\/figcaption><\/figure>\n<\/figure>\n\n\n\n

The parts came in several bags, one with switches and the other with everything else. An acrylic panel faithfully replicates the colors and logo of the PDP11\/70, along with a display case and rear panel to house the electronics and any interfaces the builder opts to include. Since the Pi includes WiFI, I’ll likely let this computer connect wirelessly, but I still included an RJ-45 ethernet port on the back to allow for a hard-wired network connection.<\/p>\n\n\n\n

The kit took about 6 hours to assemble. Included were 30 switches of various types, 64 LEDs, 37 diodes, 2 rotary encoders, 18 resistors, and an 8-channel logic driver integrated circuit. I was pleased that everything worked when I powered up the circuit board the first time. After the PDP11 replica was assembled, I added it to my network and logged in.<\/p>\n\n\n\n

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My replica PDP11 running<\/figcaption><\/figure>\n<\/figure>\n\n\n\n

I booted into BSD 2.11, an early UNIX variant, and explored the file systems. Under the \/usr\/games directory were programs called trek and hangman, both of which I used almost 50 years ago. I typed .\/trek to start the program and instantly remembered the game’s commands and strategy. It all came back to me – surprising, since I usually can’t remember what I had for breakfast on any given day. The main difference was that I was using a terminal emulator, which instantly displays the text output where the older teletype would take forever to type each character at a blazing 110 baud communication speed, adding to the sense of anticipation.<\/p>\n\n\n\n

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Running trek on my replica PDP11 with BSD 2.11 UNIX<\/figcaption><\/figure>\n<\/figure>\n\n\n\n

This PDP11 replica is mainly a novelty, but I’ve enjoyed logging onto it, booting various operating systems, compiling old software, and navigating the file system using commands from the very origins of the UNIX operating system. What a great way to revisit childhood memories from a time when computers were not yet in our homes.<\/p>\n","protected":false},"excerpt":{"rendered":"

In late 1974 I was fortunate enough to get some experience using an HP-2000F minicomputer with a teletype terminal in my school. Compared to using a computer today, the teletype … <\/p>\n","protected":false},"author":2,"featured_media":5945,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_crdt_document":"","footnotes":""},"categories":[3],"tags":[259,257,258],"class_list":["post-5935","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-projects","tag-kit","tag-pdp11","tag-pidp11"],"_links":{"self":[{"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/posts\/5935","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/comments?post=5935"}],"version-history":[{"count":13,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/posts\/5935\/revisions"}],"predecessor-version":[{"id":5963,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/posts\/5935\/revisions\/5963"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/media\/5945"}],"wp:attachment":[{"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/media?parent=5935"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/categories?post=5935"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/forths.com\/index.php\/wp-json\/wp\/v2\/tags?post=5935"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}