Path: utzoo!utgpu!attcan!uunet!microsoft!stevesc From: stevesc@microsoft.UUCP (Steve Schonberger) Newsgroups: comp.os.minix Subject: Re: Big disks, big problems Message-ID: <7917@microsoft.UUCP> Date: 1 Oct 89 22:08:01 GMT References: <3442@ast.cs.vu.nl> Reply-To: stevesc@microsoft.UUCP (Steve Schonberger) Organization: Microsoft Corp., Redmond WA Lines: 40 Andy writes: >In particular, since disk addresses are 16 bits, clearly no partition >larger than 64M can work, but how about > 32M? It is possible to work around this problem by using larger sectors. I know some of large-disk-DOS versions use this solution. The 32M limit assumes 512 byte sectors; addresses are unsigned, so with sectors of 1K you get 64M without trouble. >What about disks that are larger than 64M, but have a MINIX partition >above 64M? This probably implies longs somewhere, and I don't know if >they are used properly. Having several partitions of <32M has long been a large-disk-DOS trick. It's quite simple, I think. A third solution, using longer disk addresses, is difficult, and was likely the root of a lot of the compatibility complaints about DOS 4 (but I don't know much about DOS, and even less about DOS 4, so I'm no authority).). A very elegant solution is that of Berkeley fast file system. They use sector clusters as the allocation unit. Files that will fit whole into a cluster only use the sectors they need; files that are larger than a cluster are stored in whole clusters only. Another interesting solution, used by Microsoft's announced and maybe released OS2 High Performance File System is to use extents (starting block, length pairs) as the allocation unit, rather than individual blocks. That would be highly inappropriate for Minix though, since it is both very un-Unix-like and would require a great deal of rework to implement. -- Steve Schonberger microsoft!stevesc@uunet.uu.net "Working under pressure is the sugar that we crave" --A. Lamb Since I've mentioned products made by the company I work for, I need to emphasize my disclaimer. I know very little about DOS. I know very little about the file system part of OS2. Most important, I'm not making official announcements.