Date: Tue, 29 Jan 2002 18:14:03 -0800 (PST) From: <babkin@FreeBSD.org> To: hackers@FreeBSD.ORG, justin@mac.com Subject: Re: OS Textbook FreeBSD Appendix Message-ID: <200201300214.g0U2E3f62586@freefall.freebsd.org>
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"Justin C.Walker" wrote: > > On Monday, January 28, 2002, at 05:10 PM, Greg Shenaut wrote: > > >> I'd guess that the point deals with the use of "shared memory" between > >> processes for the purposes of sharing data. Given the granularity of > >> the PDP-11 "VM" hardware, it seemed like a bad tradeoff, and wasn't > >> considered useful until long after the PDP-11 went to the Boston > >> Computer Museum, where it sipped tea and complained about the Red Sox. > > > > Well, on PDP11s, which I used for V6, V7, and 2.8 & 2.9 BSD, you > > could share text memory, as has already been stated, and IIRC you > > could also share data memory after a vfork (once vfork became> > remember PDP/11 architecture all that well either. > > You're correct; that's what I meant by the 'granularity' of the > hardware. You had to share a fairly hefty chunk of memory, so (except > for vfork-like-things), it put too much of a constraint on the use of > the sharing. As far as I remember from reading the Lyons' book, there were 16 mapping descriptors for text and data each. I think, 1/16 of the address space is not too big, and in absolute values it's the size of today's pages (4KB). -SB To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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