From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE, MAILING_LIST_MULTI,RCVD_IN_DNSWL_NONE autolearn=ham autolearn_force=no version=3.4.2 Received: from minnie.tuhs.org (minnie.tuhs.org [45.79.103.53]) by inbox.vuxu.org (OpenSMTPD) with ESMTP id 9380c62e for ; Fri, 10 Jan 2020 15:49:04 +0000 (UTC) Received: by minnie.tuhs.org (Postfix, from userid 112) id B29AD9B843; Sat, 11 Jan 2020 01:49:02 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 099A493D85; Sat, 11 Jan 2020 01:48:39 +1000 (AEST) Authentication-Results: minnie.tuhs.org; dkim=pass (1024-bit key; unprotected) header.d=ccc.com header.i=@ccc.com header.b="i52OCJPk"; dkim-atps=neutral Received: by minnie.tuhs.org (Postfix, from userid 112) id 412A493D85; Sat, 11 Jan 2020 01:48:37 +1000 (AEST) Received: from mail-qt1-f173.google.com (mail-qt1-f173.google.com [209.85.160.173]) by minnie.tuhs.org (Postfix) with ESMTPS id 84B7A93D07 for ; Sat, 11 Jan 2020 01:48:36 +1000 (AEST) Received: by mail-qt1-f173.google.com with SMTP id e5so2273380qtm.6 for ; Fri, 10 Jan 2020 07:48:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ccc.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=jtz8bv9zimhQY4qnubTzx78H1Nfdc84Tj0vHX7zSL00=; b=i52OCJPkERxLezeWjjonTRjcFmQyw/xLqciDP8qQCtJ48ST2ADfMKROSxiDF78Xoyf /EP0miYLWW34Yz++Alqz2+srP/o8PgPDT3M056nLL8ajyN9L2aK3Z9+L0zyDSFSkdIMk 4K5uJDICsSOhORjADBPJ1xWMA81Qcd5G9dfbM= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=jtz8bv9zimhQY4qnubTzx78H1Nfdc84Tj0vHX7zSL00=; b=BTz6WudJtEqvT8fWu4BtNd4mh8KZOUP34qQ5AeT8cpqSxznl/omoqTVoe1nxRdnPwW wap+NT9fHcUy8x7gbdhynLbOjVwGmv+alLMhfmMzEyfRFOKGASolaZnpIr26Mrw5x7Jf HabacxkEZK3Y11a5wH5kN9dTGNPnnc0a9VBfaEdcQouKMcTtCEjZFFVNyjYsrtqmniFS edfere49ov0tjJ7Q9alpDJqtbuazl1dyFV170c2PSkt2bR4QScsJh4X21TU+t70a+OYv Ie+RU+6tYVUDM7xIlm2CjQ1Iv8Wuw9RL7DuSkKQTtUrH2oFy4+OtQz4Awbffc5iHRLwx qNmg== X-Gm-Message-State: APjAAAW0puz1yKKfD2sQeNPj3YbJTxDuw0LZgqhetcM9QqoEfMxusiPi 9nrPXeCsiqXfugMSCmMjdnBGxwOIS/o/teY6cFnoE11FlaygXA== X-Google-Smtp-Source: APXvYqwMqRY+I7J2dLTdaDhCRqDFeXkuq1N8uTdV9zBt8eTCmnwMO6lvN/UMiKagERC0nA+jNu08zPD5aWfgV29kS1w= X-Received: by 2002:aed:2202:: with SMTP id n2mr3087464qtc.4.1578671315516; Fri, 10 Jan 2020 07:48:35 -0800 (PST) MIME-Version: 1.0 References: <9c507ef665851fd21ecdf0e23136dc86@firemail.de> <1ippPk-8PE-00@marmaro.de> <81cf0f73-2141-10c9-7352-51c0aac76959@mhorton.net> In-Reply-To: <81cf0f73-2141-10c9-7352-51c0aac76959@mhorton.net> From: Clem Cole Date: Fri, 10 Jan 2020 10:48:09 -0500 Message-ID: To: Mary Ann Horton Content-Type: multipart/alternative; boundary="000000000000fa9313059bcb0ec9" Subject: Re: [TUHS] screen editors / machine load X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: TUHS main list Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" --000000000000fa9313059bcb0ec9 Content-Type: text/plain; charset="UTF-8" On Fri, Jan 10, 2020 at 10:00 AM Mary Ann Horton wrote: > Yes, it was a real concern. Physical memory on the shared PDP-11 was > limited, and if everyone had a separate copy of vi running the machine > would swap itself silly. > > This only mattered if everyone had their own separate copy of vi > installed. The fix was to put vi in a single system directory, such as > /usr/ucb or /exptools. The instruction part of its memory would be > shared among all the users, resulting in much less swapping. > Actually it was much worse than that... What Mary Ann points out was mostly true of your PDP-11 had DH11's installed; which had deeper hardware buffering and 16 character DMA on output. But these were expensive from DEC and also took up a 'full system unit' in the CPU for 16 lines. Until Able (much later) released the DMAX-11 (*a.k.a.* DH/DM) product of a DH11 clone on a single board, many university sites did not use them; but used multiple DL-11/KL-11's instead. If your system was configured with DL/KL11s or similar (CMU had it's own called 'ASLIs' - a synchronous line interfaces) each character took one interrupt for each either input or output. Moreover, the UARTS that DEC used which were made by Western Digital had 2 >>or less<< characters of input buffering, so they could drop chars[1]. The ASLI's used a later chip with a slightly better buffer IIRC but I admit I've forgotten the details (Jim Tetter probably remembers them). So if you had a single line, the interrupt load was huge on a PDP-11. For this reason, a lot of sites limited glass TTYs to speeds like 2400 or 4800 baud, not the full 9600. DEC later released the DZ-11 which worked on units of 8 ports per board. Unfortunately, it was not DMA and the buffering was still pretty shallow. Joy did a lot of work on 4.1BSD in the DZ driver to cut down the interrupts because 9600 baud DZ lines could swamp a vax and when running the BerkNet between systems (before UCB had ethernet), 9600 baud serial lines were standard. [1] Two things A) The original WD UART chip had very limited buffering. The timing was such that as high rates it could not empty accept a second character without the first being overwritten. This was a long-standing issue for many UARTs long in the 1990s. The original chip NS built and IBM used on the PC (the NS8250) was notorious for the same problem. By the time of Motorola's 6881, it had 8 characters of buffering IIRC. B) As I understand the history, Gordon developed the original idea of the UART at DEC for the PDP-1. But I'm not sure of the patent details. He does not list the UART patent on his web site although he does mention inventing it. I have been under the impression CMU was somehow mixed up in the patent and licensing of it, *i.e.* WD got the license from CMU to make them not DEC; which was part of why we had the ASLI's. Again, IIRC, we got the UART chips from WD at cost and could make the ALSI's locally much cheaper than DL-11s. >>I think<< the story was that one of Gordon's student's designed a chip, which WD fabbed and licensed. Before that DEC had built UARTs on boards from transistors and later logic gates. --000000000000fa9313059bcb0ec9 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Fri, Jan 10, 2020 at 10:0= 0 AM Mary Ann Horton <mah@mhorton.net= > wrote:
= Yes, it was a real concern. Physical memory on the shared PDP-11 was
limited, and if everyone had a separate copy of vi running the machine
would swap itself silly.

This only mattered if everyone had their own separate copy of vi
installed. The fix was to put vi in a single system directory, such as
/usr/ucb or /exptools. The instruction part of its memory would be
shared among all the users, resulting in much less swapping.
Actually it was much worse than that...
What Mary Ann points out was mostly true of your PDP= -11 had DH11's installed; which had deeper hardware buffering and 16 ch= aracter DMA on output.=C2=A0 =C2=A0But these were expensive from DEC and al= so took up a 'full system unit' in the CPU for 16 lines.=C2= =A0=C2=A0 Until Able (much later) released the DMAX-11 (a.k.a. D= H/DM) product of a DH11 clone on a single board, many university sites did = not use them; but used multiple DL-11/KL-11's instead.

If your system was configured=C2=A0with DL/KL11s or simi= lar (CMU had it's own called 'ASLIs' - a synchronous line inter= faces) each character took one interrupt for each either=C2=A0input or outp= ut.=C2=A0 Moreover, the UARTS that DEC used which were made by Western Digi= tal had 2 >>or less<< characters of input buffering, so they co= uld drop chars[1].=C2=A0 The ASLI's used a later chip with a slightly b= etter buffer IIRC but I admit I've forgotten the details (Jim Tetter pr= obably remembers them).

So if you had a single line, t= he interrupt load was huge on a PDP-11.=C2=A0 For this reason, a lot of sit= es limited glass TTYs to speeds like 2400 or 4800 baud, not the full 9600.= =C2=A0 =C2=A0

DEC later released the DZ-11 which worke= d on units of 8 ports per board.=C2=A0 Unfortunately, it was not DMA and th= e buffering was still pretty shallow.=C2=A0 =C2=A0Joy did a lot of work on = 4.1BSD in the DZ driver to cut down the interrupts because 9600 baud DZ lin= es could swamp a vax and when running the BerkNet between systems (before U= CB had ethernet), 9600 baud serial lines were standard.

<= div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif= ">
[1]=C2=A0 Two things
=C2=A0A) The original WD UART c= hip had very limited buffering.=C2=A0 =C2=A0The timing was such that as hig= h rates it could not empty accept a second character without the first bein= g overwritten.=C2=A0 This was a long-standing issue for many UARTs long in = the 1990s.=C2=A0 The original chip NS built and IBM used on the PC (the NS8= 250) was notorious for the same problem.=C2=A0 By the time of Motorola'= s 6881, it had 8 characters of buffering IIRC.

B) As I= understand the history, Gordon developed the original idea of the UART at = DEC for the PDP-1. But I'm not sure of the patent details. He does not = list the UART patent on his web site although he does mention inventing it.= =C2=A0 =C2=A0I have been under the impression CMU was somehow mixed up in t= he patent and licensing of it, i.e. WD got the license from CMU to m= ake them not DEC; which was part of why we had the ASLI's.=C2=A0 Again,= IIRC, we got the UART chips from WD at cost and could make the ALSI's= =C2=A0locally much cheaper than DL-11s.=C2=A0 >>I think<< the s= tory was that one of Gordon's student's designed a chip, which WD f= abbed and licensed.=C2=A0 Before that DEC had built UARTs on boards from tr= ansistors and later logic gates.

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