Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!husc6!bbn!uwmcsd1!marque!nic From: nic@marque.mu.edu (Nic Bernstein) Newsgroups: comp.sys.att Subject: Re: Missing: 5 MB on a Unix PC. Message-ID: <1912@marque.mu.edu> Date: Tue, 3-Nov-87 21:30:12 EST Article-I.D.: marque.1912 Posted: Tue Nov 3 21:30:12 1987 Date-Received: Sat, 7-Nov-87 09:08:08 EST References: <381@sdcjove.CAM.UNISYS.COM> <8700198@eta.ETA.COM> <316@zorch.UU.NET> Reply-To: nic@marque.UUCP (Nic Bernstein) Distribution: comp.sys.att Organization: Marquette University, Milwaukee, WI Lines: 59 In article <316@zorch.UU.NET> scott@zorch.UU.NET (Scott Hazen Mueller) writes: >In article <8700198@eta.ETA.COM> lm@eta.UUCP (Larry McVoy) writes: >#In article <381@sdcjove.CAM.UNISYS.COM> john@CAM.UNISYS.COM (John Dempsey) writes: >#>I think I'm missing 5 MB of memory and would like to know why. When I type: >#I didn't read this closely but I'll bet you're forgetting about /dev/swap which >#lives on a different partition of your disk. >#Sorry 5 meg. > >Close. Actually, I'd say that the swap space is 4M (remember, 4M max memory >size?) and the 5th is his alternate sectors (for bad sector replacement.) >Thus, on the 67M drive, you get 60M total space since you need 3M for bad >sectors. > >#Larry McVoy uucp: ...!{uiucuxc, rosevax, meccts, ihnp4!laidbak}!eta!lmcvoy ># arpa: eta!lmcvoy@uxc.cso.uiuc.edu or lm@arizona.edu > > >-- >Scott Hazen Mueller ( near_me ? lll-crg!csustan!helium : uunet )!zorch!scott >(209) 527-1203 scott@zorch.UU.NET Actually you are close, but not right. The pc7300/3B1 machines have a active memory limit of 4 megs. That is what you are refering to as the 4 meg max memory size. The swap space is in the first partition of the hard disk and can be almost any logical size. This is used as if it were active memory when the actual memory would overflow and the machine can page into the swap space as if it were real memory. It still only uses as many pages as it needs and if you are swapping tasks you can use all of 4 megs of memory and 4 megs of swap up. Try running several GNU-Emacs for this and then have everyone use "info" for the emacs info file. You'll use most of the active and swap up. The bad blocks are something else. The disk is formatted to have 17-512 byte sectors per track. The system uses physical blocks of 512 bytes but has logical blocks of 1024 bytes. This means the the disk is formatted for 17 blocks per sector but the system uses only 16 of the blocks. The 17th block then becomes the alternate for the bad block mapping. These are hidden to you and an "iv -vt" will only report the actual physical mapping. If you do an "iv -vt" on the disk, then the partitioning will become visible. You will probably find the 1st partition to contain 5000 blocks (the actual 1st partiton is the boot sectors, usually about 23 or 24 blocks). This is the swap area. This is caused when you first initalize the system from the "diagnostic" disk, which asks if the system will be used multi-user. If you answer yes to this question, then the default swap area will be 5 megs, if you answer no then the default swap area is 4 megs. Be careful though! If the swap area is too small then the system will kill processes (sometimes silently). We had tried to cut the swap down to 3 megs on one pc-7300 and then ran GNU-Emacs and it could never load the emacs info file, even though it loaded all the other info files properly. It turned out that the system killed the load, silently. Other things can also be a problem, 14 bit compress will run real slow on a 1meg active memory system, spending most of its time swapping things on and off the disk. Much depends on how much disk space you have to play with, but setting the swap size at 5 megs seems the best bet (hope he's not got one of those early 10 meg monsters). - Nic