Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/17/84; site nbires.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!gatech!ut-sally!seismo!hao!nbires!bob From: bob@nbires.UUCP (Bob Bruck) Newsgroups: net.micro.pc Subject: Re: How do set drive size > 10mb? Message-ID: <558@nbires.UUCP> Date: Wed, 4-Dec-85 11:28:20 EST Article-I.D.: nbires.558 Posted: Wed Dec 4 11:28:20 1985 Date-Received: Sat, 7-Dec-85 04:01:54 EST References: <970@mako.UUCP> <452@nicmad.UUCP> Reply-To: bob@nbires.UUCP (Bob Bruck) Distribution: net Organization: NBI,Inc, Boulder CO Lines: 46 >In article <970@mako.UUCP> johnco@mako.UUCP (John M. Cole) writes: >>I have need for more than 10 meg worth of storage, but when my drive is >>done formatting, it says I have ~10mb free space. Yes, the drive is larger >>than 10 mb. Is there anything obvious I have missed? > In article <452@nicmad.UUCP> brown@nicmad.UUCP (Mr. Video) writes: >Use the FDISK command and check to see if your DOS partition is set up >correctly, ie, it should be the whole disk. Also, you will need PC-DOS 3.0, >or greater. I believe that DOS 2.1 and below only knew about 10MB disks. >PC-DOS 3.0 (really 3.10 now) knows up through 33MB disks. This isn't entirely accurate, although it is close to the truth. In PC-DOS 2.x, unlike PC-DOS 3.x, the information about the format of the fixed disk partitions was determined at boot time based on the size of the disk par- titions (such as the root directory size, number of FATs, etc.). The al- gorithm used was a simple table lookup based on the number of sectors in the partition and was contained in the IBMBIO.COM startup program. This exact same algorithm was duplicated in the FORMAT routine to initiallize the partition. The FORMAT routine does place this information in the BOOT sector, but that information was not used in the startup sequence in DOS 2.x. In DOS 3.x, the startup sequence (IBMBIO.COM) reads the information about the format of the partition from the boot sector rather than determining it from the partition size. This was neccessary because the algoritm used for de- termining the format changed and they wanted DOS 3.x to be able to access disk partitions formatted with DOS 2.x. Note that partitions formatted with DOS 3.x may not be useable with DOS 2.x (the standard 10 Meg partition will work, though). Now, the reason DOS 2.x would not work with partitions larger than about 16 Meg was because of a bug in the FORMAT routine. Because of the mistaken use of a signed comparison instead of an unsigned comparison, FORMAT would only work for partitions <= 32K sectors. This bug was fixed in 3.x so that par- titions can be as large as 64K sectors. Getting back to the original problem posed by Mr. Cole, it sounds like he forgot to set the jumpers on his Fixed Disk Adapter card, so that the FDISK routine still thinks he has a 10 Meg drive. If his drive looks like one of the 4 drives in the table on the Adapter card, all he will have to do is change the jumper on the card. Otherwise, he will have to burn a new ROM for his fixed disk controller card with a table entry for his drive (is this legal???) or use an FDISK routine from a third party vendor that will enable him to describe his drive (are there any of these comercially available???). Bob Bruck (hao | allegra | ucbvax | ...)!nbires!bob NBI Inc. Boulder, Co.