STORAGE DEVICES Towards the end of this unit you will be able to identify the type of storage devices and their storage capacity
WHAT IS STORING ?
STORAGE CAPACITY Storage capacities and file sizes are measured from lowest to highest in: bits bytes kilobytes megabytes gigabytes Terabytes
Relationship between measurement 8 bits 1 byte 1024 bytes 1 kilobyte 1024 kilobytes 1 megabyte 1024 megabytes 1 gigabyte 1024 gigabytes 1 terabyte 1000 Terabyte 1 Petabyte 1000 Terabyte 1Petabyte
ACTIVITY PLACE THE FOLLOWING MEASURING UNIT IN TERMS OF THEIR STORAGE CAPACITY FROM SMALLEST TO LARGEST bits Kilobytes Gigabytes Terabytes Megabytes Bytes
STORAGE DEVICES USED IN A COMPUTER A computer uses two types of storage. A main store consisting of ROM and RAM, and backing stores which can be internal, eg hard disk, or external, eg a CD or USB flash drive.
HOME WORK DRAW THE MEASUREMENT RELATIONSHIP TABLE 8 bits……….. 1 byte. …………………………. ………………….. 1 terabyte
MAIN STORE (COMPUTER MEMORY) Main store (or computer memory) is divided into Read Only Memory (ROM) and Random Access Memory (RAM). ROM (NON VOLATILE MEMORY) ROM is memory that cannot be changed by a program or user. ROM retains its memory even after the computer is turned off. For example, ROM stores the instructions for the computer to start up when it is turned on again.
RAM RAM (VOLATILE MEMORY) In the case of RAM, it is volatile (this means that when power is switched off all of the data in the memory disappears). Main memory is used to store data whilst it is being processed by the CPU. Data can be put into memory, and read back from it, very quickly.
ROM AND RAM
INTERNAL BACKING STORE-HARD DISK The main internal backing store is a computer's hard disk. A hard disk stores: the operating system software applications or programs the majority of your data files Note: Hard disks store large amounts of data - 200GB to 1TB is common in desktop computers. The data stored on a hard disk is retained until deleted, but it needs to be loaded into main store RAM before it can be used.
HARD DISK
ACTIVITY 1.Which of the following retains its data even after the computer is switched off? ROM RAM REM 2. What does RAM stand for? random accessible memory random access memory random allowable memory 3. What is a computer's main internal backing store? CD-ROM ROM hard disk 4. How best is the size of a hard disk measured? kilobytes megabytes gigabytes
ANSWERS 1.Which of the following retains its data even after the computer is switched off? ROM RAM REM 2. What does RAM stand for? random accessible memory random access memory random allowable memory 3. What is a computer's main internal backing store? CD-ROM ROM hard disk 4. How best is the size of a hard disk measured? kilobytes megabytes gigabytes
MAGNETIC STORAGE MEDIUM-Floppy disks Floppy disks hold very small amounts of data, just 1.44MB and a computer needs a floppy drive to read them. They are used to: transfer small files of data from one machine to another backup important small files that are stored on your hard disk store restricted files that you don't want other users of your computer seeing
MAGNETIC STORAGE MEDIUM-ZIP DISK Zip disks are like large floppy disks but can store 250MB or more of data. To read them a computer needs a zip drive. Their use is similar to that of floppy disks.
MAGNETIC STORAGE MEDIUM- HARD DRIVES Hard Drives- There are two types of Hard Drives. One is Internal that we studied earlier. The other is an Portable Hard Drive. A portable hard-drive is one that is placed into a small case along with some electronics that allow the hard-drive to be accessed using a USB or similar connection. Portable hard-drives allow very large amounts of data to be transported from computer to computer. HARD DRIVES ARE RANDOM ACCESS DEVICES
MAGNETIC STORAGE DEVICES- MAGNETIC TAPE Magnetic tape are serial access devices and are used only where batch processing is used. Advantages: (i) Tape is light and compact and easy to carry and yet it stores far more data than floppy discs.