Path: ...!news.iecc.com!.POSTED.news.iecc.com!not-for-mail From: John Levine Newsgroups: comp.arch Subject: Re: ancient OS history, ARM is sort of channeling the IBM 360 Date: Wed, 26 Jun 2024 19:51:34 -0000 (UTC) Organization: Taughannock Networks Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Date: Wed, 26 Jun 2024 19:51:34 -0000 (UTC) Injection-Info: gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="41736"; mail-complaints-to="abuse@iecc.com" In-Reply-To: Cleverness: some X-Newsreader: trn 4.0-test77 (Sep 1, 2010) Originator: johnl@iecc.com (John Levine) Bytes: 2086 Lines: 21 According to Stephen Fuld : >understand why not for writes. The no crossing block boundries is a >side effect of fixed block disks. This couldn't happen in OS/360 with >CKD disks. Actually, it did. OS had a Variable Block Spanned record format that could split a logical record over several physical disk blocks. I don't think it was very widely used, but it's still there in z/OS: https://www.ibm.com/docs/en/zos/3.1.0?topic=SSLTBW_3.1.0/com.ibm.zos.v3r1.cbcpx01/spanned.html This doesn't mean it was a particularly good idea as implemented, of course. I see that VSAM now has what they call linear datasets, which we would call normal block files, which are used for Data in Virtual which we call memory mapped files: https://www.ibm.com/docs/en/zos/3.1.0?topic=guide-data-in-virtual -- Regards, John Levine, johnl@taugh.com, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. https://jl.ly