Storage Devices Chapter 7

Floppy Drive Overview The floppy drive subsystem consists of three main parts: ▫the electronic circuits or the controller, ▫the 34-pin ribbon cable, and ▫the floppy drive (sometimes called the “a” drive).

Floppy Media and Construction The media inserted in a floppy drive is a disk or floppy disk. Floppy drives have two read/write heads responsible for placing the data,

Floppy Drive Installation or Replacement Installation of floppy drives is simple after doing the following preliminary homework: ▫An available drive bay ▫An available power connection ▫A motherboard floppy connector or install an additional adapter ▫A floppy cable Figure 7.1 shows a motherboard floppy connector. Figure 7.2 shows a floppy drive cable that attaches from the motherboard to the floppy drive. ▫Keep in mind the end with the twist is the one that connects to the drive.

Hard Drive Overview The hard drive subsystem can have up to three parts: ▫the hard drive; ▫a cable that attaches to an adapter or the motherboard; and ▫control circuits located on an adapter or the motherboard.

Hard Drive Geometry Hard drives have multiple hard metal surfaces called platters. Each platter typically holds data on both sides and has two read/write heads, one for the top and one for the bottom. The read/write heads float on a cushion of air without touching the platter surface. If a read/write head touches the platter, a head crash occurs.

Each hard drive surface is metallic and has concentric circles, each of which is called a track. One corresponding track on all surfaces of a hard drive is a cylinder. Figure 7.5 show how a concentric circle makes an individual track. A single track on all the surfaces makes an individual cylinder. Each track is separated into sectors by dividing the circle into smaller pieces. 512 bytes are normally stored in each sector, as shown in Figure 7.6.

Hard Drive Interfaces Overview A hard drive system must have a set of rules to operate. These rules make up a standard called an interface that governs communication with the hard drive. There are two major hard drive interfaces: ▫IDE (integrated drive electronics), also known as the ATA (AT Attachment) standard, and ▫SCSI (small computer system interface).

Both IDE and SCSI started out as parallel architectures. This means that multiple bits are sent over multiple paths.

A serial architecture is a point-to-point bus where each device has a single connection back to the controller. Bits are sent one bit at a time over a single link.

IDE (Integrated Drive Electronics) There are two types of IDE—PATA (Parallel ATA) and SATA (Serial ATA). PATA (parallel ATA) is the older IDE type, which uses a 40-pin cable that connects the IDE hard drive to an adapter or the motherboard and transfers 16 bits of data at a time.

The newer IDE standard is SATA (serial ATA). Serial ATA is a point-to-point interface, which means that ▫each device connects to the host through a dedicated link (unlike the traditional parallel IDE where two devices share the host link), and ▫each device has the entire interface bandwidth.

eSATA (external SATA) provides external device connectivity using the SATA standard. eSATA allows shielded cable lengths up to 2 meters (~6.56 feet), with faster connections than USB 2.0 or most IEEE 1394 types. However, the eSATA connection does not provide power to external devices.

SSD (Solid State Drive) SSDs (solid state drives) are storage devices that use nonvolatile Flash memory technologies instead of hard drive technologies. Two types of technologies used with SSDs are SLC and MLC. ▫SLCs (single-level memory cells) store 1 bit in each memory cell and last longer than MLCs, but they are more expensive. ▫MLCs (multi-level memory cells) store more than 1 bit in each memory cell and are cheaper to manufacturer, but they have slower transfer speeds.