From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,3cd3b8571c28b75f X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-09-01 14:44:28 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!arclight.uoregon.edu!wn13feed!wn11feed!worldnet.att.net!4.24.21.153!chcgil2-snh1.gtei.net!news.bbnplanet.com!chcgil2-snf1.gtei.net!news.gtei.net!news.binc.net!kilgallen From: Kilgallen@SpamCop.net (Larry Kilgallen) Newsgroups: comp.lang.ada Subject: Re: A Customer's Request For Open Source Software Date: 1 Sep 2003 16:44:25 -0500 Organization: Berbee Information Networks Corporation Message-ID: References: <3F44BC65.4020203@noplace.com><20030822005323.2ff66948.david@realityrift.com> <3F4828D9.8050700@attbi.com> <3F4EA616.30607@attbi.com> <3F512BD1.8010402@attbi.com> <3F52AA5F.8080607@attbi.com> In article <3F53B88E.7040405@attbi.com>, "Robert I. Eachus" writes: > As I said, most RDBMSs already have the ability to bypass the OS and > access disk drives directly. They do ? On what operating systems ? On the one with which I am most familiar, device registers can only be accessed from the innermost mode, and the code that does that is in a device driver. If the DBMS vendor should happen to provide their own driver, installing it would make it part of the operating system. Even ADABAS, the most contrary DBMS I have encountered for system manager relations, was this way. It insisted on calculating sectors and cylinders on its own (back when there were such things), but it ended up calling the operating system's device driver to read those bits into memory. I think there are many hardware architectures that would have a hard time delivering the interrupts without going through the operating system interrupt dispatch. > This is going one step further, and > "mapping" the disk drive into memory. With a memory-mapped drive on a > virtual memory system, you can address the disk just like the memory was > physically present in RAM. I know compilers that read source that way, relying upon the OS paging in the data as appropriate. But it is an individual performance/coding tradeoff, not applied so universally as in Multics.