 |
Edited by: Florin Balasa ISBN 978-953-307-063-6, Hard cover, 226 pages Publisher: InTech Publication date: April 2010 |
Since the inception of the modern computers in the late 1940s, computing systems have continually grown in complexity, both in hardware and in the software associated systems. This complexity is due to two factors: first, the trade offs in cost/performance versus size of various memory–storage systems, and second the way users organize and use data. Modern computing systems consist of four hardware components: the central processing unit (CPU),
the main memory, the secondary storage (disks, tapes, CD, etc.) and the input-output devices that interfaces with humans. Since the beginning of the modern computer era in the late 1940s and early 1950s, the need for larger storage capabilities has become increasingly apparent.
The need for larger storage is due mainly to the vast amount of digital data including graphic, audio and video media. All computations, either mental, mechanical, or electronic require a storage system of some kind, whether the numbers be written on paper, remembered in our brain, counted on the mechanical devices of a gear, punched as holes in paper, or translated into electronic circuitry. This study reviews the evolution of the storage systems from early mechanical systems to optical storage technology. Because of the importance of the storage systems in computing, evolution of the storage systems is directly related the CSIS 550-History of Computing. Floppy Disk Drives / Floppy Disks Floppy disk drives were originally introduced commercially as a read-only device in the early 1970s. These early floppy disk drives were used to hold microcode and diagnostics for large IBM
mainframe computer systems.
These disk drives were using 8-inch floppy diskettes recorded on only one side. By changing these diskettes inside the floppy drive, technicians could easily update the microcode to the latest revisions or load diagnostics easily. The storage capacity of these early readonly drives was less than 100 kilobytes. In 1973 a new upgraded 8 inch drive with read/write capability and a capacity of about 250 kilobytes began shipping which IBM used in data entry systems. This drive incorporated many technical improvements and became a model for drives still in use today. As time went on, designers learned how to reliably record on both sides of the diskette as well as increase the density of the data recorded on the diskette. In 1976 smaller 5.25 inch size floppy drives were introduced by Shugart Associates. In a cooperative effort, Dysan Corporation manufactured the matching 5.25 inch flexible floppy diskettes.
Originally these drives were available in only a single-sided low density format, and like the first 8 inch models, stored less than 100 kilobytes. Later they received many of the same improvements made to the 8 inch models, and eventually 5.25 inch floppy drives settled at a double-sided, "double density" formatted capacity of about 1.2 megabytes. This drive was used in the IBM-AT personal computer. Modern floppy drives and diskettes (3.5 inch) have evolved to a much smaller size with larger capacities as well. In 1980, the 3.5 inch floppy drive and diskette was introduced by Sony. During the early 1980's many competing formats were tried to compete with the 3.5 inch drives. Over time the industry settled on the 3.5 inch format which was standardized and manufactured by many companies. Today's standard 3.5 inch diskettes hold a formatted capacity of 1.44 megabytes while still using the same basic technology of the second generation 8 inch drives.
The primary factor that caused engineers to reduce the size and cost of floppies was the introduction and evolution of the personal computer. It was in the personal computer market that the low cost, mass produced floppy drive found its first real home. Very quickly, the floppy became the standard method of exchanging data between personal computers. It also became the popular method of storing moderate amounts of information outside of the computer's hard drive. Floppy diskettes are small, inexpensive, readily available, easy to store, and have a good shelf life if stored properly. It is a round, flat piece of Mylar coated with ferric oxide, a rustlike substance containing tiny particles capable of holding a magnetic field, and encased in a protective plastic cover, the disk jacket.
Data is stored on a floppy disk by the disk drive's read/write head, which alters the magnetic orientation of the particles. Orientation in one direction represents binary 1; orientation in the other, binary 0. Hard-Disk Drives (Hard Disks) The hard drive, also called the hard disk or fixed disk, is the primary storage unit of the computer. It is always labeled the C drive. Additional drives are labeled after it as the D, E, F, etc. It has several read/write heads that read and record data magnetically on platters, a stack of rotating disks inside the hard drive. Hard drive is important for the following reasons:
· It stores programs that must be installed to the hard drive before they can be used.
· It stores data files that can be accessed later.
· It organizes files like a file cabinet so they can be accessed more easily.
The Hard Drive can store a large amount of computer data on it. Many advancements have made it possible to store a large amounts of data in a small space. The hard drive's speed is discussed in terms of access time. This is the speed at which the hard drive finds data. The average access time is measured in milliseconds. One millisecond equals 1/1000 of a second. The average drives had 9 to 14 ms access time. The lower the access time the faster the hard drive. The capacity, or amount of information that a hard drive can store, is measured in bytes. Today many computers come with 20- 80 GB (Giga Byte=1,000 Mega Bytes) hard drives.
Types of Hard Drives
(1) Bournolli has a mechanism that acts as a fly wheel. When the HD spins the disk follows gravities course and is lifted up a few centimeters causing the Read/Write heads to touch. When it stops spinning, the HD will fall back down the few centimeters.
(2) Magnetic Optical Drive has the best storage capacity. It has the same principles as the Bournolli, but is mixed with the Compact Disc technology so that the Read/Write head puts data in order and the laser reads off of it.
(3) Standard Magnetic Drive The standard magnetic drive is less complex and less expensive than the others. It stores data with a read/write head which sends a pulse of electricity through causing the magnetic films electrons to line up in a certain way.
No comments:
Post a Comment
leave your opinion