Number 231 - July 2002

Big Disk Limits
by Dick Maybach, Brookdale Computer Users Group
The various components in a PC have evolved over the years, and this can cause problems when you upgrade your system. In particular, old motherboards were not designed to operate with today's multi-gigabyte hard drives, and there are several well-known limits you should be aware of to avoid disappointment. Many of these applied to systems that are now obsolete, and I won't cover them here. I'll limit myself to Windows 95 and later operating systems and to hardware manufactured during or after 1994. If you have an older system, or if you want a more thorough explanation, please check the PC Guide, www.pcguide.com. This is an excellent resource for software and hardware information that its author, Charles Kosierok, updates frequently. BIOS Limits     If you have an old (pre 1994 or so) BIOS that does not support disk geometry translation, your PC will not see more than 528 MB on any hard disk. (By the way, there are two ways to measure disk capacity. Here, I'll use a strictly decimal notation, but many authors and programs use hybrid binary/decimal notation that denotes 1024 as 1K and 1024 x 1024 = 1,048,576 as 1M, which I think is confusing. In this article, 1K = 1000, and 1M = 1,000,000.) The 528-MB problem was solved around 1995 by new BIOS designs and by enhanced disk driver software such as Western Digital's Ontrack. Check your BIOS set-up screens that deal with hard disks and look for options such as LBA (Logical Block Addressing), ECHS (Extended Cylinder, Head, Sector), or just Large. These indicate that your BIOS does not have the 528 MB limit.     A short time later, in 1996, some BIOS bugs imposed a limit of 2.11 GB, and after this people found various other bugs that limited disk sizes to around 3, 4, or 34 GB. Check the above Web site or your BIOS vendor to see if they affect you. The solution to all these problems is to upgrade your BIOS or to use an EIDE expansion card that contains a BIOS extension.	File System Limits     The FAT16 file system imposes a 2.15 GB limit on partition size, regardless of how modern your BIOS is. DOS, Windows 3.1, and early Windows 95 use FAT16. Note however that this does not limit the total hard disk size, which is determined by the BIOS or the file system. If you have Windows 95 OEM SR2 or a later system, you can use FAT32, which can accommodate partitions of up to 8 GB. Windows 95 does not have any provisions to upgrade the file system, so you must use Partition Magic or a similar program to do this. If you have Windows 98 or later, it can upgrade your old FAT16 partitions. Operating System Limits     DOS, versions 6.22 and earlier, and Windows NT, versions 3.5 and earlier, support disk sizes only up to 8.46 GB. Microsoft has announced that Windows 95 will never support disks larger than 32 GB, regardless of the version or your BIOS and the file system you use. They have given no explanation for this. Windows 98 and ME may need a patch for disks larger than 32 GB; check with Microsoft before you buy a disk larger than this.     Different Microsoft operating systems support different file systems. DOS and early Windows 95 support only FAT16. Windows 95 OEM SR2, Windows 98, and Windows ME support FAT16 and FAT32. Windows NT supports FAT16 and NTFS (NT File System). Windows 2000 supports FAT16, FAT32, and NTFS. This means you have to be careful if you dual-boot your PC. For example, if you want to run both 95 and NT on the same machine, you must store your data on a FAT16 partition to allow both operating systems to see it. Disk Hardware Limits     ATA (IDE) disks are limited to 137 GB. This isn't a problem yet, but will surely become one soon. Look for a new hard disk standard in the next year or two, which will probably be incompatible with current BIOS's, disk controllers, and software.
Number 231 - July 2002