Storing Data

Memory vs. Storage

Storage devices are like file drawers, in that they hold programs and data. Programs and data are stored in units called FILES. The files are stored in digital envelopes called DIRECTORIES.

Why is storage necessary?Storage retains data when the current is switched

off.

• The computer’s random-access memory (RAM) is volatile. All the information in RAM is irretrievably lost.

• Storage devices are nonvolatile. They do not lose data when the power goes off.

Why is storage necessary cont’d. . .

• Storage is cheaper than memory, RAM is designed to operate very quickly so that it can keep up with the computer’s CPU.

• Storage devices do not transfer data as rapidly as memory, but they are much less expensive. A computer system’s storage devices typically holds much more data and software than the computer’s memory.

• Storage devices also play an important role when you start an application.

• Storage devices are increasing in capacity to the point that they can hold an entire library’s worth of information.

Storage Sizes

Term Abbreviation Bytes (approximate)

Kilobyte K or KBone thousand

Megabyte M or MBone million

Gigabyte G or GBone billion

Terabyte T or TB one trillion

Types of storage devices

Read/Write media vs. Read-only media

Most storage devices are read/write media. They enable the computer to perform writing (output) operations as well as reading (input) operations.

Some storage devices are read only, operations. CD-ROM drives are read only devices; CD-RW drives are read/write media.

Sequential vs. Random-Access storageStorage devices are categorized

according to the way they get to the requested data. In a sequential storage device, such as tape backup unit, the computer has to go through a fixed sequence stored items to get to the one that’s needed.

A random-access storage device can go directly to the requested data without having to go through a sequence. This device is faster and more expensive.

Storage Hierarchy

Storage devices fit into one of three locations in the storage hierarchy. They are differentiated by their availability of the data they contain.

1. Online storage – primary storage. It consists of the storage devices that are actively available to the computer system and do not require any action on the part of the user. The computer’s hard disk is a personal computer’s online storage system.

2. Near-Online storage – secondary storage that’s not directly available but require some simple action (s) on the user’s part. Eg. Inserting a disks (floppy disks and CD-ROMS)

3. Offline storage – tertiary storage or archival storage (not readily available). Such as the magnetic tapes, are used for infrequently accessed data that needs to be kept for archival purposes. Some personal computers are equipped with tape drives, which can be use for archival storage.

Capacity of storage devices

A storage device’s capacity is measured in bytes (a unit of data composed of eight bits).

A 2 GB or 4 GB disk may be needed to hold these items plus software. A scientist working with laboratory data may need 50 GB of storage, while a huge corporation may need several terabytes of storage to hold all the information it works with.

Access Time: Memory vs. Storage

Device Typical access time

Static RAM (SDRAM) 5-15 nanoseconds

Dynamic RAM (DRAM) 50-70 nanoseconds

Solid state disk (SSD) 0.1 milliseconds

Hard disk drive 6-12 milliseconds

CD-ROM drive 80-800 milliseconds

Speed of storage devices (access time)

A storage device most important characteristic – the speed with which it retrieves the desired data – is measured by its access time, the amount of time it takes for the device to begin reading the data.

Eg. Disk drives – the access time includes the seek time, the time it takes the read/write head to locate the data before reading begins.

Formatting: preparing disks for use

Before a magnetic disk can be used for storage, it must be prepared using a process called FORMATTING.

You can format floppy disks yourself using the formatting utility supplied with the computer’s operating system. However, you will seldom need to do so. Most of the floppy disks are preformatted.

Be aware that formatting destroys all the data that has been recorded on a disk.

You should never format the computer’s hard disk, unless you have just purchased a new hard disk and are following the installation instructions.

Formatting

• Double click on My Computer

• Select the drive

• Right click on mouse

• Format: following the instructions

• Select start

Virtual MemoryTo increase your virtual memory:

1. My computer Right click

2. Properties then advanced

3. Setting then advanced

4. Virtual memory change

The standard is 744 but you can increase to 800 = 1 GB or 1000 depending on how much you have available.

CLASS WORK TIME

IN YOUR NOTEBOOKS OR ON FOLDER SHEET, COMPLETE THE FOLLOWING:

1. State two reasons why storage is necessary

2. Explain the difference between memory and storage

3. Explain the difference between Read-only and Read/Write

CLASS WORK TIME Cont’d

IN YOUR NOTEBOOKS OR ON FOLDER SHEET, COMPLETE THE FOLLOWING:

HOMEWORK:

• Create a conversation dialogue (i.e. between two persons) explaining to someone is unsure of how to format and save their information on a flash drive.

Dialogue should be no more than a page long.