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My computer doesn't recognize my new larger hard drive

Taken from PC Magazine (Oct 2002)

Every few years, PC users grapple with hard drive size limitations. Some restrictions, such as the 2GB partition limit under FAT16, are caused by the operating system's file system. Others are caused by

the PC's BIOS, which is the lowest-level interface to the hardware. Regardless of the cause, these limitations often prevent the system from recognizing or using all of the hard drive's space. For example, a system may only see 32GB of your 40GB hard drive. The only way to take full advantage of the space has been to perform upgrades.

Today, PC users are faced with another pressing hard-drive size limit: 137GB. Fortunately, hard drive and computer makers are working together to break this limit using Big Drives technology, which will let computers work with hard drives that can store petabytes (PB, or millions of gigabytes). We'll look at the reasons for hard drive size limits, explain the benefits of Big Drives technology, and show you how to support the new standard on your PC.

Note that in measurements of storage or RAM, the kilo-, mega-, and giga- prefixes are based on the binary system. A kilobyte is 210 (1,024) bytes, a megabyte is 220 (1,048,576) bytes, and a gigabyte is 230 (1,073,741,824) bytes. Windows measures your machine's RAM, file sizes, hard drive free space, and hard drive capacity this way.

Drive vendors, however, treat those prefixes as decimals. When listing drive specs, they round kilobytes to 103 (1,000) bytes, megabytes to 106 (1,000,000) bytes, and gigabytes to 109 (1,000,000,000) bytes. To avoid confusion, we'll stick with the drive makers' preference.

Understanding how hard drive size limits arise requires that you know a few things about how data is stored and retrieved. Data on your drive is placed on platters that spin under read/write heads. The platters are divided into concentric rings (or cylinders), and each cylinder is divided into sectors. Once the drive knows the cylinder, head, and sector, it can locate a precise position for reading or writing. This is called CHS (or cylinder/head/sector) addressing. The maximum values for the early CHS addressing scheme were 1,024 cylinders, 16 heads, 63 sectors, and 512 bytes per sector. This presented the industry with its first size limit: 528,482,304 bytes.

Drive makers overcame this limitation quickly in the early 1990s by adding BIOS extensions to support LBA (logical block addressing). Rather than specifying a particular cylinder, head, and sector, LBA uses a 28-bit address to define 228 (268,435,456) unique sectors. A controller embedded in the drive translates each sector into an appropriate physical location. Because each sector can hold 512 bytes, LBA can support drives up to 137,438,953,472 bytes (137GB).

Note that although LBA always supported 137GB capacities, BIOS makers frequently did not support the full 28-bit addressing scheme. This resulted in size limits at 8GB and 32GB, which were easily corrected with a BIOS upgrade (or a new drive controller card).

Pushing the Limits

Hard drives already exceed 120GB, so the industry will soon need an addressing scheme that supports drives larger than 137GB. Rather than create a new scheme in place of the standard ATA/ATAPI-6 storage interface, Technical Committee T13 (a part of the International Committee on Information Technology Standards, www.t13.org) endorsed a 48-bit (6-byte) addressing standard that would break the barrier. Drive maker Maxtor, along with Compaq, Microsoft, and VIA, began to promote the specification under the name Big Drives in 2001.

48 bits lets you address 248 (281,474,976,710,656) sectors, and at 512 bytes per sector, drives can be up to 144,115,188,075,855,872 bytes (144PB). That's an astonishing 144,115,188GB. The number of sectors transferable with a single command also increases, from 256 to 65,536, boosting data-transfer performance. Even with the rapid growth in drive sizes, 48-bit addressing is expected to support new drives for the next 20 years.

Get Compliant

To work in a PC, Big Drives requires support from the BIOS, the hardware, and possibly the operating system (via drivers). Before you purchase a drive larger than 137GB, take some time to verify the other elements of your PC.

First, check with your system manufacturer to see whether the BIOS version is recent enough. You can find the BIOS version in the text string that appears following power-on, or in BIOS Setup mode, which you enter by pressing the Ins, Del, F1, or F2 key during boot-up, depending on the BIOS. The code that appears after the name of the BIOS maker (usually AMI, Award, or Phoenix) is the version. Your manufacturer may tell you that the system already supports Big Drives, or recommend a BIOS upgrade or a controller card that will do the trick.

The BIOS and the South Bridge chip of your motherboard's chip set must work together to support Big Drives. Late-model Intel chip sets (including the 810, 815, 820, 830, 840, 845, 850, and 860 sets) can be Big Drives–compliant with Intel's Application Accelerator software (www.intel.com/support/chipsets/iaa). The free IAA utility for Windows 98, Me, NT 4.0, 2000, and XP enables the chip set to support 137GB hard drives and larger. Windows 95 uses a FAT16 file system, which limits partitions to 2.1GB, so Big Drives technology isn't a sensible choice.

Most current non-Intel chip sets also support the new technology. For example, the VIA VT8233A South Bridge chip is Big Drives–compliant at UDMA/133 speeds, and it is often included with the VIA KT333 or the VIA P4X266A. Check the downloads area of each manufacturer's site for BIOS updates that may help compatibility with 137GB and larger drives.

Upgrade the Controller

Big Drives technology has been around since September 2001. Systems that shipped prior to that will probably not be fully compliant. If your system doesn't support Big Drives natively, or you're just not sure, consider upgrading your drive controller using a PCI expansion card, such as the Maxtor Ultra-ATA/133 PCI adapter or the Promise Technology Ultra133 TX2 controller.

Update the OS

If your BIOS can handle hard drives larger than 137GB, you won't need new drivers, but you will need drivers for your OS if you're adding Big Drives support via a controller card. You must install the drivers before you install a high-capacity hard drive. As a rule, you should install the new controller alongside your current controller, then install any drivers for your OS from the manufacturer's CD. Once the Device Manager correctly identifies the controller, you can power down the PC and transfer your drives to the new controller ports. Disable the old controller ports if necessary—usually through the BIOS Setup.

At some point in the future, PC users may require an OS patch or update to overcome other possible drive size limits. Although 48-bit addressing will allow incredibly large hard drives, all current Windows platforms—including Windows XP—use 32-bit addressing. This imposes a partition limit of 2.2TB (2,200GB, or 232 sectors at 512 bytes per sector).

Choose a Drive

With hardware support settled, it's time to select a hard drive. Maxtor's D540X line includes UDMA/133 drives up to 160GB (model 4G160J8). It's only a matter of time until other drive makers release drives with capacities above 137GB.

Big Drives hard drives use the same 40-pin IDE interface as smaller-capacity drives, but the drive circuitry is updated to support the additional addressing bits and to decode the related commands. Big Drives controllers still support older drives (those with capacities below 137GB or slower than UDMA/133), though. Both drive types will work off the same controller, so you don't need to abandon existing drives.

Install a Controller

We mentioned earlier that updating the drive controller is a good way to ensure Big Drives compatibility. Here, we'll discuss the basic installation for a Big Drives controller. Keep in mind that you should always refer to the manufacturer's documentation for specific installation and setup instructions. Also note that there is a small risk of data loss when upgrading the drive system, so be sure to back up any important work before proceeding.

Always start by powering down the PC, unplugging the power cord, and opening the outer case; you should be able to see the motherboard and its available PCI slots. Remove a cover plate from an available slot, insert your new controller card, and screw the card to the chassis. You can also connect the hard drive activity LED cable to a connector on the controller card, if you'd like.

If you're building a new system and your hard drives are currently empty, the BIOS will recognize them, and you can attach them to the new controller card now. If you have an existing system with a working OS and data on your hard drives, you'll need to install drivers for the new controller before moving your hard drives to it. We'll assume that you're upgrading an existing system, so leave your drives on the old controller for now.

Power up the PC, and allow the operating system to boot. Windows 98, Me, and XP should detect the new controller hardware as PCI Adapter. Open Device Manager. Expand the Other Devices entry; you'll probably see an entry for a generic PCI Mass Storage Adapter. Highlight this and click on Properties. Select the Driver tab and click Update Driver to start the Update Device Driver wizard. Insert the new drive controller's CD into the CD-ROM drive, and follow the wizard to update the driver for your specific card (for example, a Maxtor Ultra-ATA/133 Adapter). Finish the installation, remove the driver CD, and reboot the computer.

Confirm that the new controller card is properly installed by starting the Device Manager and looking for the new controller's entry under SCSI Adapters (or SCSI and RAID controllers under Windows XP). Don't be thrown by the SCSI reference; it's a quirk of Windows. If you still have a PCI Adapter entry under Other Devices, the new controller has not been installed correctly.

Under Windows NT 4.0 and 2000, install the new controller and then power up the PC. Select Start | Settings | Control Panel | SCSI Adapters. When the SCSI Adapters dialog opens, click on Drivers and select Add. The Install Drivers dialog opens; click on Have Disk. Insert the driver CD and make sure the CD-ROM drive is on the list of drives to search, then click on OK. The Install Driver dialog opens. Select the driver for your particular controller, and click on OK. When the Select SCSI Adapter Option dialog opens, click Install. After installation, the SCSI Adapter Setup dialog will show that the new controller was installed.

Transfer the Drives

After the new controller card is installed and the OS drivers updated, power down the system and transfer your drives from the current controller (usually integrated into the motherboard) to the new controller. This typically involves disconnecting the IDE cable connector at the motherboard and reconnecting it to the corresponding port on the new controller card.

As the system reboots, start the BIOS Setup and disable the old (motherboard) drive controller channels so that only the new drive controller is recognized. Some PCs may disable the old controller automatically if no drives are attached, but it's worth a check just to make sure. Save any changes to the BIOS Setup and reboot the system. The system should boot normally.

In rare instances, you may find that you can't boot the system once the new controller is installed and the drives are transferred. In this case, you have to change the Boot Order in the BIOS Setup so that SCSI is the first entry.

Now install the drive. Power down, then configure the Big Drive's master/slave jumper. Bolt the Big Drive into place and connect the power. Connect the 40-pin/80-wire cable between the drive and the new controller. Boot to the BIOS setup and see that the new drive is auto-detected and auto-configured properly. Reboot with a Windows Startup Disk. Partition the drive with FDISK. If this is a secondary drive, just format the drive with FORMAT. Boot normally, and you're done. If this is a primary drive, install Windows (remember those new drivers for the controller), and setup will run FORMAT for you. Once your changes are made, your operating system will be able to see your old and new drives.