CHAPTER 7 Storage1. Storage 课件.ppt

1、CHAPTER 7 Storage,Storage,When a computer is first switched on, it needs to load up the BIOS (Basic Input/Output System) and basic instructions for the hardware.,These are stored in ROM (Read Only Memory).,This type of memory is called non-volatile because it retains the data.,Data stored in ROM rem

2、ains there even when the computer is switched off.,ROM can be found on the motherboard.,Read Only Memory (ROM),Computers store temporary data in the RAM (Random Access Memory). These could be operating instructions, loose bits of data or content from programs that are running.,The contents of RAM ar

3、e constantly rewritten as the data is processed.,When the computer is switched off, all the data is cleared from the RAM.,This type of memory is called volatile because it only stores the data whilst the computer is switched on.,RAM sticks are found on the motherboard.,Random Access Memory (RAM),RAM

4、 and ROM,Computers need backing storage outside the CPU to store data and programs not currently in use. There are three main types of storage device:,Those that store data by magnetizing a special material that coats the surface of a disk.,Those that store data using optical technology to etch the

5、data onto a plastic-coated metal disk. Laser beams are then passed over the surface to read the data.,Flash drives use solid state technology and store data in a similar way to the BIOS chip.,Types of backing storage,Types of backing storage,The medium is what the data is actually stored on. Example

6、s of media include floppy disks, CD-ROMs and zip disks.,Floppy disks hold about1.44 MB of data.,Zip disks store up to750 MB of data.,CDs hold around 700 MB of data.,The hard disk of the computer stores the system information, programs and data that the computer uses every day. Computer servers will

7、use RAID systems with many hard drives to provide huge capacity and safer storage. The drives can be mirrored so that data written to one of them is also written to others, so if one drive fails, the others just take over. Removable hard drives plug into the USB port and can be used for backup or tr

8、ansfer of data to another computer.,Backing storage hard drives,Floppy disks used to be used a lot, but they are unreliable and dont hold very much data, so they are rarely used now. They hold 1.44 MB of data, so are only really useful for backing up or moving small files that dont contain graphics.

9、 They are easily damaged, which means that files stored on them wont always load. As flash memory has become cheaper, many new computers dont even have a floppy disk drive.,Backing storage floppy disk drives,There are two main types of optical storage: CD and DVD. They look exactly the same, but DVD

10、s hold much more data than CDs and need different drives to read them.,CD-ROMs are read only you can read data from them but cant write more data to them. CD-Rs allow you to write data once, but you cant write over it. CD-RWs allow you to write data and then record new data over it. DVD-Rs and RWs f

11、ollow the same pattern. You need special software to write to CDs and DVDs you cannot simply copy files to them.,Backing storage optical,In recent years, flash memory has become much more popular.,It holds a lot of data in a very small space. It doesnt need special software to use it. Most computers

12、 will recognize the device as soon as you plug it in. Flash memory sticks connect through USB or FireWire ports. Many other devices, like digital cameras and MP3 players, also use flash memory. Flash memory cards can hold different types of data so your MP3 player could hold a data file with your ho

13、mework on it, for example.,Backing storage flash memory,Data is stored using binary code (0 and 1). Computer memory is measured in kilobytes. Read Only Memory (ROM) is non-volatile because it cannot be changed. Random Access Memory (RAM) is volatile because it only works when the computer is switched on. There are three types of storage device: those that use magnetic media, others that us