c8902348@wombat.newcastle.edu.au (05/15/91)
In article <1991May13.215237.4309@d.cs.okstate.edu>, mmccorm@d.cs.okstate.edu (McCormick Martin) writes: > > From: halpern@casbah.acns.nwu.edu (David Halpern) > I've recently installed dos4.0 on my pc and everytime I boot I guet this > warning message telling me to install share for large media. I should also > add that I have a 286pc with 20MB and 40MB hard drives. Why am I getting > this message and what should I do to stop getting it ? > ------------------------------------------------------------------------ > Please post to the group. Obviously, we could install SHARE, but > I'd really rather know the reason for this message. Without digging > through the DOS manual, I recall that SHARE.EXE has to do with opening > and sharing data files between applications. > > Martin McCormick > Amateur Radio WB5AGZ > Oklahoma State University > Stillwater, OK Its basically this.. Because DOS 4 introduced a new File Descriptor format some programs that do naughty things, like bypassing Bios/DOS could relly stuff up your hard disk.. So share is there for large drives to fix thios problem. Also share is used for MultiTasking/LAN operations (MultiUSER), to regulate who can have the file open at the same time.. Ie.. If you were to have two applications writing to the same file at the same time, you can imagine the problems that would cause, so basically it would let the first application to open the file to have exclusive access to it.. And make the other application wait till the first is finished.. Well this is a simple view of it.. Its much more involved than this.. Tony
cctr132@csc.canterbury.ac.nz (Nick FitzGerald, CSC, Uni. of Canterbury, NZ) (05/16/91)
In article <1991May15.113950.1@wombat.newcastle.edu.au>, c8902348@wombat.newcastle.edu.au writes: > In article <1991May13.215237.4309@d.cs.okstate.edu>, mmccorm@d.cs.okstate.edu (McCormick Martin) writes: >> >> From: halpern@casbah.acns.nwu.edu (David Halpern) >>>I've recently installed dos4.0 on my pc and everytime I boot I guet this >>>warning message telling me to install share for large media. I should also >>>add that I have a 286pc with 20MB and 40MB hard drives. Why am I getting >>>this message and what should I do to stop getting it ? >> >> Please post to the group. Obviously, we could install SHARE, but >> I'd really rather know the reason for this message. Without digging >> through the DOS manual, I recall that SHARE.EXE has to do with opening >> and sharing data files between applications. > > Its basically this.. Because DOS 4 introduced a new File Descriptor format > some programs that do naughty things, like bypassing Bios/DOS could > relly stuff up your hard disk.. So share is there for large drives > to fix thios problem. Nearly but not quite. The old (DOS 1.X) file handling routines used FCB's rather than file handles - the MS recommended way since they were introduced (in DOS 2.0 ?). The problem with using FCB's on large partitions is that the FCB can only address appox 30Meg of disk space and attempts to write past this limit causes arithmetic overflow (or "wrap-around" - not sure which is best term) resulting in the boot-record, the FAT's, root directory and so on being overwritten. To avoid the possibility of problems like this DOS 4.X tries to automatically load SHARE at boot if it detects large media. SHARE was used as it already contained code to "convert" FCB type disk I/O into appropriate file handle type calls. Of course this was very clearly and fully documented in all the Manuals and other reference material distributed with DOS 4.X so all users with large media would understand the significance of needing to load SHARE and the risks of not doing so. (For the uninitiated, the following sentence is what is kown around these parts as sarcasm - for any MS/IBM documentation writers who might be reading (if you can 8-) ) there's something there for you to think about.) The risks are, in reality, _very small_, but the potential damage is _very great_. If you don't want to load SHARE just to protect the file integrity of your 200Meg HD there are a couple of small PD (?) utils NOSHARE and NOTSHARE that intercept FCB calls and return a "fail" to the originating process (the latter is floating around the net as part of someone's sig). --------------------------------------------------------------------------- Nick FitzGerald, PC Applications Consultant, CSC, Uni of Canterbury, N.Z. Internet: n.fitzgerald@csc.canterbury.ac.nz Phone: (64)(3) 642-337