From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 4247 invoked from network); 13 Dec 2022 15:12:35 -0000 Received: from minnie.tuhs.org (50.116.15.146) by inbox.vuxu.org with ESMTPUTF8; 13 Dec 2022 15:12:35 -0000 Received: from minnie.tuhs.org (localhost [IPv6:::1]) by minnie.tuhs.org (Postfix) with ESMTP id 247A3423B8; Wed, 14 Dec 2022 01:12:13 +1000 (AEST) Received: from mail-ua1-f43.google.com (mail-ua1-f43.google.com [209.85.222.43]) by minnie.tuhs.org (Postfix) with ESMTPS id 64B5941C30 for ; Wed, 14 Dec 2022 01:12:08 +1000 (AEST) Received: by mail-ua1-f43.google.com with SMTP id ay42so2374043uab.6 for ; Tue, 13 Dec 2022 07:12:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dartmouth.edu; s=google1; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=WJfyrqaIW9w9w4no5+LXn9byonD0Bzu7emlhBRkuY04=; b=jGtHS7uW2UHw5Z3yjrj2Wfk4sb+pRBOmoa7R0P2n1i9x9dmhPMnHw813gfOzaj1f0u 9R6fObolcaxKIVhGfLLhh85ZHIzRv/ICYaBDtWzSfXfpiOkEdCd5IxuRzgRhDblKwFWY oShdNyJqOdTo7A5YJPPYs9atB8k5db63rpVUMAObwQx4yvgp4roFZf2kf46yrjgT4VXi M6Q05lzRr+3QnnCaXmUcTK/+zyRmoNLMif/a8y4No9lKLHtteknfnlAXqnmKADTfxr57 PJj+dvY1jNdxDQ2jZ5wD5hxJTHoAMTQgU1T6MVbjKCbv+YjUSLIQSDT7602ZvSA+rGSo rkTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=WJfyrqaIW9w9w4no5+LXn9byonD0Bzu7emlhBRkuY04=; b=gITLU3p+uflxlw8GCwfcAx0ZIBjbFu1rfQyNs1zwKCiLtFp2gyDXbqySc61Jj2BOV6 MHMFmNuyCaXMnCicKiZ3roaFV3nxnHBU/6vBOxuwndJQLC2qZYKf1Vu53rWyxWC7hEJ3 CDjQACsJrBImhKkL/PmmX/OvsOuPYMyDHCz50MGGL+kEW26sRBk1uXJNju/y281i40hV l29gB3quojWXX05a/N0NlP2uHJkaHC5OoPPz5jPrCdjDQwHW0CfYxSK1v9Is8MhbWgKs eCCYDa3l4o7OmP7W0t80WVoPLlf9attd54igKnJC1vi0CqdVtmB3N3HwiujrSQYHD/kc i7lw== X-Gm-Message-State: ANoB5pmd8rzw8FtXEeWbFCxIrD+q8ilH4Ey7a7WuXCNZbR3S9lKtKnVg BQx2Fv+zwW6UYX9gzlSovQnEuMIBnjw/dHY+131F+A== X-Google-Smtp-Source: AA0mqf5zjvz7JAIxNFEYAa5xC/uLXslMxUWy5mwVzFMAK8zyRLdqCnh8a9C8AqCWHkxU2ndngQZ37wIr7aNjMCga4lc= X-Received: by 2002:ab0:3899:0:b0:419:1b4a:360b with SMTP id z25-20020ab03899000000b004191b4a360bmr30732531uav.102.1670944267375; Tue, 13 Dec 2022 07:11:07 -0800 (PST) MIME-Version: 1.0 References: <202212131431.2BDEVCls018959@freefriends.org> In-Reply-To: <202212131431.2BDEVCls018959@freefriends.org> From: Douglas McIlroy Date: Tue, 13 Dec 2022 10:10:51 -0500 Message-ID: To: arnold@skeeve.com Content-Type: text/plain; charset="UTF-8" Message-ID-Hash: 2TZNJAUQO36DRB35S3AZ5UDTFZOQEM7X X-Message-ID-Hash: 2TZNJAUQO36DRB35S3AZ5UDTFZOQEM7X X-MailFrom: douglas.mcilroy@dartmouth.edu X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; header-match-tuhs.tuhs.org-0; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: tuhs@tuhs.org X-Mailman-Version: 3.3.6b1 Precedence: list Subject: [TUHS] Re: Clever code List-Id: The Unix Heritage Society mailing list Archived-At: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: A delay line is logically like a drum, with circulating data that is accessible only at one point on the circle. A delay line was effectively a linear channel along which a train of data pulses was sent. Pulses received at the far end were reshaped electronically. and reinjected at the sending end. One kind of delay line was a mercury column that carried acoustic pulses.. The PB 250 delay line was magnetostrictive (a technology I know nothing about). If instruction timing is known, then the next instruction to appear is predictable. The only caveat is that instruction times should not be data-dependent. You can lay out sequential code along the circle as long as no instruction steps on one already placed. When that happens you must switch modes to jump to an open spot, or perhaps insert nops to jiggle the layout. Doug On Tue, Dec 13, 2022 at 9:31 AM wrote: > > Douglas McIlroy wrote: > > > Apropos of accessing rotating storage, John Kelly used to describe the > > Packard-Bell 250, which had a delay-line memory, as a machine where > > addresses refer to time rather than space. > > > > The PB 250 had two instruction-sequencing modes. In one mode, each > > instruction included the address of its successor. In the other mode, > > whatever popped out the delay line when the current instruction > > completed would be executed next. > > > > Doug > > For us (relative) youngsters, can you explain some more how delay > line memory worked? The second mode you describe sounds like it > would be impossible to use if you wanted repeatable, reproducible > runs of your program. > > Thanks, > > Arnold