TOPIC 4—FIXED HARD DISK SYSTEMS

The following guidelines will help you keep your disk pack in peak condition: Always keep the disk pack in its container when it is not being used. Reassemble the disk pack canister, even when it is empty. Never touch the disk pack’s recording surfaces. Do not expose the disk pack to stray magnetic fields. Always store a disk pack flat. Never store a disk pack on its edge. Store the disk pack in the same environment in which the disk memory set operates. TOPIC 4—FIXED HARD DISK SYSTEMS Fixed hard disk systems are commonly found in minicomputers and microcomputers. They are called fixed disks because the disk is enclosed in a sealed case and is inaccessible to the user. The technology of these disk drives is one of the fastest changing in the computer world. In the 14 years that fixed disks drives have been in common use, capacities have increased from 10 megabytes on a 5.25-inch full height drive, to over 10 gigabytes on a 3.5-inch half height drive. Additionally, data transfer rates have increased ten-fold, while the average seek times have decreased from more than 85 milliseconds (ins) to less than 10 ms. The cost of these systems has also decreased significantly. A 10 MB drive originally cost about $1,500.00 or an average of $150.00 per megabyte of disk space. Today the cost is less than $0.25 per megabyte. FIXED HARD DISK DRIVE CONSTRUCTION Most fixed disk systems have the same basic components and similar operational characteristics. A typical hard drive’s components include: Disk platters Head actuator assembly Read/write head assembly Cables and connectors The heads, head actuator, and platters are usually contained in a sealed unit commonly referred to as a head disk assembly (HDA). The HDA requires a dust free environment when opened to avoid contaminating the disk. Figure 10-18 illustrates atypical fixed disk. Figure 10-18.—A typical fixed disk drive assembly. 10-23