1. CHAPTER 7
STORAGE

2. Objectives
Explain the two categories of storage: Primary and Secondary.
Identify the different types of primary storage:
RAM
ROM
PROM
EPROM
Identify the different types of Secondary storage:
Magnetic Tape
Magnetic Disks
Optical Disks
Understand the benefits of memory
Explain the many types of memory.
Introduction to bits, bytes and their higher powers.
Understand how the hard drive work
Understand the two types of magnetic discs:
Floppy disk
Hard Disk

3. Objectives – Continued.
Identify the parts of the hard disk:
Tracks, Sectors, Cylinders etc.
Describe the Evolution of hard disk
Explain Removable Storage Devices: CD’s, DVD’s, Floppy disks, Flash Drives etc.
Identify all the components of storage as it relates to CD-ROMs and CD-rewritable
Understand the different types of storage devices by a comparative tabular study.
Explain the alternative storage concepts such as backup options and the online storage options.
Understand the File Systems and folders structure.
Explain the methods used to keep the computer efficient and maintain memory.

4. STORAGE
All computers and servers used today contains one or more hard-disk drives. Every types of computer such as desktop, laptop, mobile devices, mainframe and even a super computer are typically connected to a hard drive.
Storage provides all users and computers the ability to remember things when the power is turned off.
There are many different types of storage devices which provides you with a wide variety of methods for different uses.

5. PRIMARY & SECONDARY STORAGE

6. TYPES OF PRIMARY STORAGE
RAM (“Random Access Memory”)
Called “RAM” because any location in the memory can be directly accessed in the same amount of time as any other location. RAM is a major component of personal computers. RAM is the fastest storage device, and is accessed at the speed of the microprocessor. Most software has a minimum RAM requirement. RAM can be installed on the motherboard, or installed in expansion slots in a computer displayed in the above image.
ROM (``Read Only Memory'')
Is what it says: contains programs and/or data ``burned in'' at the time of manufacture. Commonly used to contain programs to ``boot up'' the computer when it is switched on.

7. TYPES OF PRIMARY STORAGE
PROM (``Programmable Read Only Memory'').
ROM which is ``blank'' and into which programs and/or data can be written, but only once.
EPROM (``Erasable Programmable Read Only Memory'').
PROM which can be erased, usually by exposure to UV light through a transparent window above the chip.

8. MEMORY
Main memory also known as the Primary Storage keeps track of what is currently being processed. It's volatile, meaning that turning the power off erases all of the data.
The computer main memory uses RAM, or Random Access Memory. These memory chips are the fastest, but most expensive, type of storage.
Storage devices are used by the processor to temporarily or permanently store data so that it can be retrieved at a later time. Ex. Random Access Memory

9. TYPES OF SECONDARY STORAGE
Secondary storage is non-volatile meaning all data contents retained when power is in the off position. i.e. does not require electrical power to retain its contents. This type of storage is relatively permanent ``not part of the internal system further away'' from the central processing unit CPU.
The basic types of secondary storage are:
Magnetic tape
Magnetic disk (``hard'' and ``floppy'')
Optical disk (CD-ROM, WORM, MO).

10. BITS AND BYTES One bit represents one "0/1" switch.
The smallest piece of information possible: On/Off, True/False, Yes/No.
One byte represents 23 bits = 8 bits.
A byte is eight bits (a nibble is four bits). A single byte can store a number between 0 and 255 (28-1). A lowercase "b" usually means bit, while an uppercase "B" usually means byte.
After that, we increment bytes by powers of 10.

11. BITS AND BYTES One Kilobyte (KB) = 210 Bytes = 1024 Bytes
= 213 Bits = 8192 Bits
Most files on your computer, or downloads from the Internet, are measured in KB. This page is about 8 KB in HTML format.
One Megabyte (MB) = 210 Kilobytes = 1024 Kilobytes
= 220 Bytes = Bytes
= 223 Bits = Bits
Your computer's memory is typically measured in MB. Large computer files, especially images, music, or video, are often in this range. 1 MB = 1,024 KB.

12. BITS AND BYTES – Continued.
One Gigabyte (GB) = 210 Megabytes = 1024 Megabytes
= 220 Kilobytes = Kilobytes
= 230 Bytes = Bytes
= 233 Bits = Bits
Hard disk capacities are measured in GB these days, but most hard disk manufacturers measure their disk sizes in SI units rather than powers of 2 ("K" to them means 1,000 instead of 1,024). This means an 80 GB hard disk is really only 74.5 GB in size when comparing against other types of storage devices.
One Terabyte (TB) = 210 Gigabytes
= 220 Megabytes
= 230 Kilobytes
= 240 Bytes
= 243 Bits
A Terabyte is approximately one trillion bytes, or 1,000 Gigabytes. There was a time that I never thought I would see a 1 Terabyte hard drive, now one and two terabyte drives are the normal specs for many new computers.

13. HOW IT WORKS? (HARD DRIVE)
A hard drive has only a few basic parts. They can have one or more shiny silver platters in which the information is stored magnetically.
The interior of a hard drive has an attached arm mechanism that moves a tiny magnet called a read-write head back and forth over the platters to record or store information.
The hard drive uses an electronic circuit to control everything which performs a bridge between the hard drive and the rest of your computer.

14. MAGNETIC DISKS
The magnetic disk is the most common form of secondary storage used today. Magnetic disks come in two forms:
hard disks
floppy disks
Hard disks are (usually but not always) permanently mounted inside the computer. All magnetic disks have a magnetically iron oxide coating and read/write heads that can move over the surface of the disk, which is spinning underneath.

15. ITS PARTS: MAGNETIC DISKS

16. ITS PARTS: MAGNETIC DISK
Data on the disk surface is recorded on tracks (magnetic, not physical grooves!) which form concentric circles on the disk.
Each disk has a set number of tracks.
Tracks with the same number on each disk (recording) surface form a cylinder.
Data is read/written when the required sector on the track rotates into position under the read/write head (note that data can be accessed from any track of the cylinder).
The time taken to position the head over the correct track/cylinder is called the seek time.
The time needed for the sector to arrive (once the head is in position over the correct track/cylinder) is called the latency time.
Creating the magnetic tracks on a previously blank disk is called formatting the disk.

17. PAST TO PRESENT: MAGNETIC DISK

18. REMOVABLE STORAGE Magnetic Floppy Disks
Current size is 3.5" diameter (older floppy disks were 5.25" and 8" in diameter).
Organized into clusters, tracks and sectors, like their hard disk.
Floppy Diskette
Which today are now phased out. This was one of the first form a storage media. This was is also an electronic medium storage device.
Reading from and writing to were both possible. Storage capacity 360K MB. This device is no longer used and is obsolete.

19. REMOVABLE STORAGE Diskette (Typically referred to as the “a:” drive)
Has also pretty much phased out. An electronic medium storage device.
Reading from and writing to were both possible. Storage capacity 720K MB.
Zip Disks
100 or 250 MB ZIP disks, designed for use in 100 or 250 MB ZIP drives, which could be an external drive, or part of the box.
Note that the device size (100 or 250 MB) and disk size (100 or 250 MB) must be compatible.

20. REMOVABLE STORAGE
Compact Flash drives, also known as Thumb drives or USB drives are portable, erasable and re-writable data storage devices. They are small and easily transportable – can fit in your pocket or wallet or on a keychain, and tend to be tough – not too easily damaged. They attach to your computer through USB ports.
Memory sticks and other compact media (e.g., micro SD cards, more common to phones, e-readers and cameras) are increasing versatile and vary in capacity. New gadgets, including a drive that reads micro SD cards and can be inserted like a USB flash drive are now available.

21. REMOVABLE STORAGE CD-ROM
Stands for ``Compact Disk - Read Only Memory''.
Comes with data already stored on it - like a music compact disk.
Useful for distributing information that should not be changed (e.g. encyclopedias) and programs (e.g. new versions of software) and, inevitably, games.
Typical storage capacity: 650 Mb.
New technology, known as DVD, will store up to 4G per disk. DVD disk drives are required to read these disks.
Typical data access time: milliseconds, although this is steadily improving and should shortly be comparable with magnetic hard disks.
Easy to handle, and relatively robust.

22. REMOVABLE STORAGE CD-Rewriteable
These are the optical version of magnetic hard disks - that is, data can be written to them and erased from them.
Similar in storage capacity and access time to the other types of optical disks.
Data is written by heating a spot on the disk with a laser beam, in the presence of a magnetic field, the direction of which determines whether a `0' or `1' is written.
Data is read by shining a lower power laser beam onto the disk spot (without the magnetic field) and detecting the polarization of the light that is reflected.
CD-R/W - Compact Disk-Read/Write.
However, care must be taken in selection of type of CD and method of “writing” to the CD – which can also depend upon the type of drive available in your computer.
Some CD’s can only be written to once, and cannot be erased and overwritten. Other CD’s are designed for re-writing.

23. REMOVABLE STORAGE DVD (Digital Video Display)
These drives are currently a common option on computers.
They often come in combination with a CD-R/W drive; DVD-ROM and DVD- R/W drives are both available.
More and more software, especially with complex graphics (particularly games) is distributed on DVD, which have larger storage capacity than CD’s.

24. REMOVABLE STORAGE DVD (Digital Video Display)
These drives are currently a common option on computers.
They often come in combination with a CD-R/W drive; DVD-ROM and DVD- R/W drives are both available.
More and more software, especially with complex graphics (particularly games) is distributed on DVD, which have larger storage capacity than CD’s.

25. REMOVABLE STORAGE Magnetic Tape
This is oldest, and originally the only, form of secondary storage.
It is still used, mostly for backup or archival storage, and for batch processing.
Data is stored on tracks on the tape - most tapes have 9 tracks.

26. COMPUTER STORAGE DEVICES

27. ACCESSING DATA
The concept access time is the time required by the CPU of the computer to access one byte of information on a device for example: hard-drive, CD, DVD, flash drive, etc. It is always good to have fast access time. The Access time is always measured in milliseconds.
Early machines (for example: The famous Intel machine) had access times of 88 milliseconds.
CD-ROM drive, 200 milliseconds.
Todays, hard disk drives have access times of 15 milliseconds or less.
In general, the higher the storage device, the faster the access time.

28. ALTERNATIVE STORAGE
Network drives: In a network environment, the designated “server” typically houses “network” drives that allow for both for shared access to files among network users, as well as secure back-up. Computers can be attached to the network physically through cable connections, or via wireless connection.
Online or internet storage houses data on computers that act as web servers. Data stored online can then be accessed from any computer with internet access.

29. ALTERNATIVE STORAGE
“Cloud” storage is a model of networked storage where data is stored in virtualized pools which are generally hosted on one or more web servers. Hosting companies operate large data centers, and users buy or lease storage capacity from them. Physically, the data storage resource may span across multiple servers. The security of the files depends upon the hosting websites. “Dropbox” is one well known example of a cloud storage company.
VPN or a Virtual Private Network provides a secure connection via the internet from any computer to a networked computer. Essentially, this is a service that allows you to operate one computer from another through the internet. When the VPN type software is housed on a network, you can log in to a computer on the network through the internet, allowing remote access to networked resources.

30. DRIVES AND PARTITION
In Windows, when you open "My Computer", you'll see a list of all of the "[disk] drives" that the operating system knows about, helpfully named using a letter of the alphabet (e.g. C:, D:, E:). Windows actually calls these "logical drives".
A logical drive can correspond to a physical hard disk, or it may in fact correspond to just part of a disk (a "partition") or even a hard disk that's not actually installed on your PC but is located somewhere on the network.
Once a partition is created for your hard drive it is quite difficult to change its size without losing all of the data on the partition.

31. FILESYSTEMS
A filesystem is a low-level organization of a logical drive's recording surface. Only one filesystem may be installed on a logical drive. "Formatting" is the process used to install a filesystem on a logical drive.
Filesystems allow us to organize our data into files and folders.
Filesystems also provide other attributes that apply to files and folders: read-only, modification date, hidden files, whether the file is ready to be archived

32. FOLDERS
A folder is a "logical container of files and other folders." It's a "logical" container because the physical disk structure of a folder has nothing whatsoever to do with the files and folders that are inside.
Folders are used to organize the files on a computer into a human-understandable hierarchy. Folders form a tree structure (actually an upside-down tree), starting at the "root" folder.

33. COMPUTER CARE
First, computers must be kept clean. This means insisting on no food or drink near the computer, and regular cleaning of dust and debris.
Second, computers should be kept at moderate temperature (between 45 and 85 degrees F). High or low temperatures may damage motherboard memory and disk drive memory.
Third, computers and disks must be kept clear of static. Since information is stored via magnetic fields, static electricity can destroy stored information. Similarly, static electricity can destroy RAM prior to installation in a computer. Computer memory, when shipped, comes packed in static proof wrap. Special care and grounding will minimize the chance that memory will be destroyed during installation. Low static carpeting may be a good investment.