Understanding Secondary Storage: Types, Advantages, Disadvantages, and Evolution, Lecture notes of Architecture

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Auxiliary Storage

Introduction

Memory Hierarchy What is Secondary Storage? The Advantages of Secondary Storage The Disadvantages of Secondary Storage Evolution of Secondary Storage Devices Types of Secondary Storage Types of Optical Disk Why we use Secondary Storage Devices

Memory hierarchy

 Computer memory divide in to detail levels as a memory hierarchy  "Memory hierarchy" in computer storage distinguishes each level in the "hierarchy" by response time.  Since response time, complexity, and capacity are related the levels may also be distinguished by those factors as well.  There are four major storage levels,  Internal – Processor registers and cache.  Main – the system RAM and controller cards.  On-line mass storage – Secondary storage (Auxiliary Storage).  Off-line bulk storage – Tertiary and Off-line storage.

Secondary Storage (Auxiliary

Memory)

Secondary Storage (Auxiliary

Memory)

• Used in a computer system to overcome the limitations of primary storage,
• Has virtually unlimited capacity because the cost per bit of storage is very low,
• Has an operating speed far slower than that of the primary storage,
• Used to store large volumes of data on a permanent basis,
• Also known as auxiliary memory.

Disadvatages

• While RAM electronic storage devices are fast, secondary storage devices are slower because they are electro-mechanical.
• The information on the secondary device has to be first located, then copied and moved to the primary memory or RAM.
• Takes more time.

Evolution of Secondary Storage

• The first hard drive was used in 1956 which is created by IBM and whose capacity was 5 MB.
• In 1971, IBM introduced a technology called the floppy disk,
• At the beginning of the 1980s the first optical devices were released by Sony and Philips. This drive can store approximately 650 to 700 of data.
• From 1990 to till now there are many devices is created like card reader, Memory Stick, Multimedia Card etc.

Tape Backups/Magnetic Tapes

• Oldest storage device,
• Used for large computer like mainframe computers,
• Made of plastic coated with magnetic material,
• Store data permanently,
• Used to read and write data,
• Cost of storing data is expensive,
• Used in reels.

Tape Backups/Magnetic Tapes

 Hard drives may fail-data must be backed up onto another storage medium  Provides ability to periodically copy the contents of data from usual storage device to a tape cartridge device.  Use tape magnetic tape medium for storage instead of disks and it is slow.  Can store large amounts of data internally or externally.

Hard Disks

• Usually used as secondary storage,
• Also called fixed disk,
• Consists of one or more metal plates,
• Metal plates are coated with magnetic material to store data,
• Also have an access arm and read / write heads.

Hard Disks

 The first hard disk consists of one or more platters inside of an air-sealed casing.  Internal hard disks reside in a drive bay and connect to the motherboard using an ATA, SCSI, or SATA cable, and are powered by a connection to the PSU (power supply unit).  Desktop hard disks consists of the following components: head actuator, read/write actuator arm, read/write head, spindle, and platter. On the back of a hard drive is a circuit board called the disk controller.  External hard disks also available with 32GB, 1000GB, 5000GB, 1TB ect.

Floppy Disks

 Diskettes.  Flexible disk and Floppies  The plastic disk inside the diskette cover is flexible  Portable storage media  Floppy disk drives (FDD)  Store data and programs by altering the electromagnetic charges on the  Disk surface to represent ones and zeroes.  Characters are represented by positive + and – charges using ASCII code.

Traditional Floppy Diskette

3.5 inch, 1.44 MB