Hard Disk Drives

When the power to a PC is switched off, the contents of memory are lost. It is the PC’s hard disk that serves as a non-volatile, bulk storage medium and as the repository for a user’s documents, files and applications. It’s astonishing to recall that back in 1954, when IBM first invented the hard disk, capacity was a mere 5MB stored across fifty 24in platters. 25 years later Seagate Technology introduced the first hard disk drive for personal computers, boasting a capacity of up to 40MB and data transfer rate of 625 KBps using the MFM encoding method. A later version of the company’s ST506 interface increased both capacity and speed and switched to the RLL encoding method. It’s equally hard to believe that as recently as the late 1980s 100MB of hard disk space was considered large. These days, this would hardly be enough to install the operating system, let alone a huge application such as Microsoft Office.

The average size of the hard disk rose from 100MB to 1.2GB in just a few years and by the start of the new millennium a typical desktop hard drive stored 18GB across three 3.5in platters. Thankfully, as capacity has gone up prices have come down, improved areal density levels being the dominant reason for the reduction in price per megabyte.

Nowadays hard drive capacities are Terabytes in size.

Read page 44 of the textbook “Exploring Computer Hardware”.

Go through the lesson content below.