Hard Drives

The hard drive first appeared in the IBM PC/XT and stored a whopping 10MB of data. Most people never dreamed they could ever use that much storage space. Today, hard drives can store more than 9GB of data. While most computers on store shelves have at least a 1 GB hard drive, a 2GB hard drive is fast becoming the norm. Hard drives of the past used either an ST-506 interface or an ESDI (enhanced small device interface) to transmit data to other parts of the computer. Today's hard drives use either SCSI (small computer system interface) or IDE (integrated drive electronics) drives. A hard drive consists of several disks, or "platters" Data is stored on hard drives in bytes. The bytesare arranged into groups of 512 bytes, which are called sectors. Sectors are grouped together intoconcentric tracks. Tracks are sometimes referred to as "cylinders," but this is a mistake. Cylindersare actually made up of a single track that runs through the platters. Tracks are circles and if youstack circles on top of each other, you will get a cylinder. The number of tracks on each platter isidentical to the number of cylinders on the hard drive. This is why manufacturers list information about the number of cylinders and don't usually list any track information.

Floppy Drives

Floppy drives have been designed in many sizes. The first floppy drive in a PC could hold 160Kbytes of data. When IBM introduced the PC/XT, it came with a 360K diskette drive. These were called floppy drives because the diskettes that were used in the drives were very flexible. Eventually, a 1.2MB diskette with this same construction was introduced. Even though the 1.2MB looks identical to the 360K diskette, it is constructed using different materials and stores data in adifferent way. You may be tempted to format a 360K diskette to 1.2MB, but you will get several badsectors during the format process. You should always use the appropriate diskette to avoid data loss.In the late 1980s, the 3.5-inch diskette was introduced. This new diskette could hold 720K of data.This diskette also came in a harder case than previous diskettes. A spring-loaded door closed overthe opening to the magnetic media when the diskette was removed from the drive. Today these3.5-inch diskettes can hold up to 2.88MB of data, but the norm is 1.44MB. Diskette drives use MFM to encode data on the disks. This is the same encoding method the first hard drives used. Access times for most floppy drives are greater than 100 milliseconds (ms). This compares to less than lOms for most new hard drives.

Expansion Cards

Expansion cards, also called adapters, allow you to add devices to your PC. These devices canrange from CD-ROMs to video display devices. Expansion cards vary according to the bus theywere designed for. The most common type of expansion card is the 16-bit ISA card. Expansion cards plug into slots on the motherboard. Most expansion cards have external connectors to attach external devices to the computer. Below is a list of some of the more common types of expansion cards:
 

Some expansion cards are multifunction cards. These cards combine several controllers onto onecard. An example of this would be an input/output (I/O) card that has serial ports, a parallel port, agame port, a hard drive controller and a floppy controller all on a single card. You may find severalof these devices integrated on the motherboard.