35 lines
1.7 KiB
Markdown
35 lines
1.7 KiB
Markdown
---
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layout: post
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title: Booting PDP-11 BASIC
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date: 2016-10-21 23:00:00
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permalink: /blog/2016/10/21/
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machines:
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- id: test1120
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type: pdp11
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debugger: true
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autoMount: ''
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config: /devices/pdp11/machine/1120/basic/debugger/machine.xml
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---
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[PDPjs](http://www.pcjs.org/devices/pdp11/machine/) can now simulate a PDP-11/20. It was one of the first PDP-11
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models, and since it had no MMU, it was limited to a maximum of 56Kb of RAM (or as DEC would say, 28K words), since
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the top 8Kb (or 4K words) of its 16-bit address space was reserved for UNIBUS devices.
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The first PDPjs test of a PDP-11/20 machine was running [PDP-11 BASIC](/apps/pdp11/tapes/basic/), by loading
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it directly into memory from the original paper tape image. This required changes to the [RAM](/modules/pdp11/lib/ram.js)
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component, including a new *loadImage()* interface that understands DEC's paper tape format.
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To provide a more "authentic" experience, there is also a new [PC11 Paper Tape](/devices/pdp11/pc11/) component,
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and machines can now be configured to include a virtual paper tape reader, with an [assortment of paper tapes](/apps/pdp11/tapes/)
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ready to be loaded.
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In the real world, before you could load *any* paper tape, you had to first enter a
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[Bootstrap Loader](/apps/pdp11/boot/bootstrap/). PDPjs has simplified that process by including the "Bootstrap Loader"
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as just another paper tape image that you can read directly into memory, using the **Read** button. Once that has been
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done, you can then load any other paper tape image using the Bootstrap Loader, once you **Load** it into the paper tape
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reader.
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{% include machine.html id="test1120" %}
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*[@jeffpar](http://twitter.com/jeffpar)*
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*Oct 21, 2016*
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