Path: csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!news.glorb.com!feed.news.qwest.net!mpls-nntp-07.inet.qwest.net!news.qwest.net!not-for-mail Message-ID: <4DC4390F.9040401@eisner.decus.org> Date: Fri, 06 May 2011 13:08:15 -0500 From: G Cornelius Organization: Dis User-Agent: Debian Thunderbird 1.0.2 (X11/20070113) X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.os.vms,alt.sys.pdp11,comp.sys.dec,vmsnet.pdp-11 To: rgilbert88@comcast.net Subject: Re: Y3K for PDP-11 Operating Systems References: <4d99c3b6$0$23756$14726298@news.sunsite.dk> <4dc032d4$0$313$14726298@news.sunsite.dk> <7d287cc3-4605-49a0-826e-fb92fc14e98d@j28g2000vbp.googlegroups.com> <92bjl8F19sU1@mid.individual.net> <92d114Fhm7U1@mid.individual.net> <92ddfkF764U1@mid.individual.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Lines: 35 NNTP-Posting-Host: 4e49aab1.news.qwest.net X-Trace: DXC=A:11QHWiHdH9DA_04m28ER\IJYZO1_H39oBmTIA\LXWeLEflS64bTjofOOP76Cf[[DcO X-Complaints-To: news@qwest.net Xref: x330-a1.tempe.blueboxinc.net comp.os.vms:2697 comp.sys.dec:413 Richard B. Gilbert wrote: > I have no PDP-11. I had one at work many long years ago. I don't miss it. You must never have worked on an -8! A 22-bit PDP-11 with RSX-11M+ (I/D space, supervisor mode libraries) was a huge improvement over the sad little 18-bit beasts (physical address, of course). And memory resident overlays at least meant that you did not have to wait for more than a single system call's overhead for additional segments of your overlaid program to be accessed. But, oh, the task builder overlay description language files you had to manage! The 18-bit physical address space was a broken concept from the beginning: "Hey, we have all this 18/36 bit stuff already built for the 10- and 20-series, let's give the 11's two entire bits of extended physical address!" To go to 22 bits your device drivers still had to go through the 18 bit atrocity, with the extra two bits tucked into the CSR somewhere, just so they could address a set of "Unibus mapping registers" to extend the map from 18 bits to 22 bits. In retrospect it all seems to have been rather poor planning. If in fact your code fit into the address space and did not need 32 bit arithmetic, it could be fast. The first time I started working in a group that had VAXen I noticed two 750's sitting off to the side because they had not been able to handle the application load. Their replacement: a pair of 11/84's. Granted, this was specialized in that the language interpreter had to do a lot of single byte operations, resulting in the initial versions, on 750's at least, being rather inefficient. Sometimes extra bits just mean extra overhead. George