Talk:SITS - Revision history

Jnc: /* Virtual memory? */ DEC engineers' opinion on what it was

2022-11-04T15:54:54Z

‎Virtual memory?: DEC engineers' opinion on what it was

Jnc: /* Category */ Yeah, direct links will probably do it

2022-10-31T18:23:34Z

‎Category: Yeah, direct links will probably do it

Jnc: /* Virtual memory? */ Atlas virtual memory was to give the illusion of more memory than physical

2022-10-31T18:08:25Z

‎Virtual memory?: Atlas virtual memory was to give the illusion of more memory than physical

Larsbrinkhoff: /* Category */ No big deal.

2022-10-28T18:56:31Z

‎Category: No big deal.

Jnc: /* Category */ A few ideas - none of them really good

2022-10-28T18:33:58Z

‎Category: A few ideas - none of them really good

Larsbrinkhoff: /* Category */ What to name it?

2022-10-28T17:53:08Z

‎Category: What to name it?

Jnc: /* Category */ That was a suggestion, really

2022-10-28T16:44:45Z

‎Category: That was a suggestion, really

Larsbrinkhoff: /* Category */ Ok!

2022-10-28T15:35:59Z

‎Category: Ok!

Jnc: /* Category */ new section

2022-10-28T14:33:24Z

‎Category: new section

Larsbrinkhoff: /* Hardware support */ No EAE, no EIS.

2022-10-27T17:11:57Z

‎Hardware support: No EAE, no EIS.

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 :::: [[MERT]] actually makes use of the PDP-11 MMU to map multiple independent segments into the process address space.
 :::: Unix stacks have been automatically expandable since [[UNIX V5]]; see [https://minnie.tuhs.org/cgi-bin/utree.pl?file=V5/usr/sys/ken/trap.c here]. [[User:Jnc|Jnc]] ([[User talk:Jnc|talk]]) 19:07, 31 October 2022 (CET)
 ==Hardware support==

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	::::: It's not a super big subject, and I don't think I'm planning on adding more articles. I'm fine with having them link to each other and people navigating that way. It's no big deal to me either way. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 20:56, 28 October 2022 (CEST)		::::: It's not a super big subject, and I don't think I'm planning on adding more articles. I'm fine with having them link to each other and people navigating that way. It's no big deal to me either way. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 20:56, 28 October 2022 (CEST)
		+
		+	Hmm. To me, categories are mostly for finding things ''easily''. (See, e.g. my recent [[:Category: File Systems]].) I guess from that point of view, a Category:SITS would mostly be useful for finding ''other'' SIS articles; and if there are only a few, as you point out, having explicit links is just as good. One wouldn't use a SITS category to find SITS itself; [[:Category: PDP-11 Operating Systems]] would get you there. So I guess we don't really need it. [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 19:23, 31 October 2022 (CET)

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 ::: Speaking about the PDP-11 hardware. Yes, the initial 11/45 processor handbook used the term segments, but every later documentation changed the term to pages. And I would argue that pages are a more correct term for what the PDP-11 MMU have. Segments are usually described by a base address and a length, and all your address space are then remapped based on this. The PDP-11 MMU have 8 pages. Each start at a fixed virtual address, 8K apart. One page seamlessly starts where the previous one ends, and it's based on the virtual address that you use. Thus, depending on how much space we're talking about, you are going to be using one or several pages to map this. And of course, the mapping for each page do not care about what the mapping for the previous page was. No need for contiguous physical memory to map your virtual memory. The main reason some people want to talk about the PDP-11 MMU pages as segments are because there is a high level of control of the size of the page. Which basically means the pages are not fixed in size (well, the have a max size that you can't go beyond), which was traditionally seen on other machines. But nowadays, this is actually pretty common on most architectures. Almost no modern architecture have just one fixed size page anymore. And the size of the pages have grown. The 8K size of the PDP-11 page is not even considered that big by today's standards. So there is pretty much nothing about the PDP-11 MMU pages that match what a segmented memory model works like, but pretty much everything is the same as most any other paged MMU. So why should we not call it pages?
 :::
-::: Finally, demand paged systems can certainly be done on a PDP-11, even if it is hard to find examples of it being done. You could argue that the stack handling in BSD on the PDP-11 is using demand paging. Memory is not allocated for much of a stack when a program starts. When references happen below what is currently allocated for the stack, the stack is grown, and the additional memory gets mapped in as needed. However, once it's been mapped, it is then always in the address space, and a valid mapping exists at all times when the process is executing. So it's not a fully demand-paged example, but a bit of a hybrid thing.
+::: Finally, demand paged systems can certainly be done on a PDP-11, even if it is hard to find examples of it being done. You could argue that the stack handling in BSD on the PDP-11 is using demand paging. Memory is not allocated for much of a stack when a program starts. When references happen below what is currently allocated for the stack, the stack is grown, and the additional memory gets mapped in as needed. However, once it's been mapped, it is then always in the address space, and a valid mapping exists at all times when the process is executing. So it's not a fully demand-paged example, but a bit of a hybrid thing. --[[User:Bqt|Bqt]] ([[User talk:Bqt|talk]]) 17:50, 27 October 2022 (CEST)
-::: --[[User:Bqt|Bqt]] ([[User talk:Bqt|talk]]) 17:50, 27 October 2022 (CEST)
 ==Hardware support==

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	:::: Here are some ideas: 'SITS Operating System', 'Small ITS' (which seems to be the first-level expansion of 'SITS'). None of them strike ''me'' as really good - but I can't come up with any others.		:::: Here are some ideas: 'SITS Operating System', 'Small ITS' (which seems to be the first-level expansion of 'SITS'). None of them strike ''me'' as really good - but I can't come up with any others.
	:::: A separate question: no matter what the name, do you think that it is worth having a separate 'SITS' category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 20:33, 28 October 2022 (CEST)		:::: A separate question: no matter what the name, do you think that it is worth having a separate 'SITS' category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 20:33, 28 October 2022 (CEST)
		+
		+	::::: It's not a super big subject, and I don't think I'm planning on adding more articles. I'm fine with having them link to each other and people navigating that way. It's no big deal to me either way. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 20:56, 28 October 2022 (CEST)

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	::: I meant it seriously. I thought just "SITS" was a boring name, so I was hoping you had something better in mind. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:52, 28 October 2022 (CEST)		::: I meant it seriously. I thought just "SITS" was a boring name, so I was hoping you had something better in mind. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:52, 28 October 2022 (CEST)
		+
		+	:::: Ah, OK. Now I am glad I asked!
		+	:::: Here are some ideas: 'SITS Operating System', 'Small ITS' (which seems to be the first-level expansion of 'SITS'). None of them strike ''me'' as really good - but I can't come up with any others.
		+	:::: A separate question: no matter what the name, do you think that it is worth having a separate 'SITS' category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 20:33, 28 October 2022 (CEST)

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	:: As you may know, in English, the phrase 'if you insist' is often used in an ironic way, not seriously. Your command of English is very good, so you might indeed be using it in the 'native' way - but I'm not sure! For the record, I don't ''insist'' on the category; I was merely ''suggesting'' (really!) it. 18:44, 28 October 2022 (CEST)		:: As you may know, in English, the phrase 'if you insist' is often used in an ironic way, not seriously. Your command of English is very good, so you might indeed be using it in the 'native' way - but I'm not sure! For the record, I don't ''insist'' on the category; I was merely ''suggesting'' (really!) it. 18:44, 28 October 2022 (CEST)
		+
		+	::: I meant it seriously. I thought just "SITS" was a boring name, so I was hoping you had something better in mind. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:52, 28 October 2022 (CEST)

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	: Oh sure, if you insist. Please create the category. I can update the articles. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 17:35, 28 October 2022 (CEST)		: Oh sure, if you insist. Please create the category. I can update the articles. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 17:35, 28 October 2022 (CEST)
		+
		+	:: As you may know, in English, the phrase 'if you insist' is often used in an ironic way, not seriously. Your command of English is very good, so you might indeed be using it in the 'native' way - but I'm not sure! For the record, I don't ''insist'' on the category; I was merely ''suggesting'' (really!) it. 18:44, 28 October 2022 (CEST)

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	I think there are enough SITS articles to warrant a SITS category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 16:33, 28 October 2022 (CEST)		I think there are enough SITS articles to warrant a SITS category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 16:33, 28 October 2022 (CEST)
		+
		+	: Oh sure, if you insist. Please create the category. I can update the articles. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 17:35, 28 October 2022 (CEST)

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	: I don't remember any more why EAE was enabled, but I tested it now and it works fine without. EIS is not needed. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:11, 27 October 2022 (CEST)		: I don't remember any more why EAE was enabled, but I tested it now and it works fine without. EIS is not needed. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:11, 27 October 2022 (CEST)
		+
		+	== Category ==
		+
		+	I think there are enough SITS articles to warrant a SITS category? [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 16:33, 28 October 2022 (CEST)

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	: Yeah, in ''theory'' one ''could'' plug an [[KE11-A Extended Arithmetic Element]] - a UNIBUS device - into an -11/45, but why would one do so? Everything the KE11 could do (MUL, DIV, ASH, etc), the native instruction set on the -11/45 already did. I too suspect that someone wrote 'EAE' when they meant '[[EIS]]' (which was standard on the -11/45; although it was an option in the -11/40.) [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 18:27, 27 October 2022 (CEST)		: Yeah, in ''theory'' one ''could'' plug an [[KE11-A Extended Arithmetic Element]] - a UNIBUS device - into an -11/45, but why would one do so? Everything the KE11 could do (MUL, DIV, ASH, etc), the native instruction set on the -11/45 already did. I too suspect that someone wrote 'EAE' when they meant '[[EIS]]' (which was standard on the -11/45; although it was an option in the -11/40.) [[User:Jnc\|Jnc]] ([[User talk:Jnc\|talk]]) 18:27, 27 October 2022 (CEST)
		+
		+	: I don't remember any more why EAE was enabled, but I tested it now and it works fine without. EIS is not needed. [[User:Larsbrinkhoff\|Larsbrinkhoff]] ([[User talk:Larsbrinkhoff\|talk]]) 19:11, 27 October 2022 (CEST)