1. Memories and storage devices

2. Units of Measurement for Storage :-
Description
1 bit
1 binary digit
1 nibble
4 bits
1 byte
8 bits
1 kilobyte (1KB)
1024 bytes
1megabyte(1MB)
1024 KB
1 gigabyte (1GB)
1024 MB
1 terabyte (1TB)
1024 GB
1 petabyte (1PB)
1024 TB
1 exabyte (1EB)
1024 PB
1 zettabyte (1ZB)
1024 EB
1 yottabyte (1YB)
1024 ZB

3. Primary Storage Devices
Primary storage is characterized by faster access time, less storage capacity & higher costs as compared to secondary storage units.
Primary storage or main memory is part of computer system which stores programs , data & intermediate results during program execution.

4. RAM RAM (Random Access Memory) is volatile memory.
i.e. when we switch off computer then contents of this memory get vanished/loosed.
It is possible to randomly select & use any storage location for storage & retrieval of data.
It is also known as ‘primary memory’ , ‘main memory’ or ‘read/write memory’ because data can be both read & written onto these units.

6. Types of Ram :- 1) Dynamic RAM(DRAM) :-
This type of memory must be constantly refreshed or else it will lose its contents.

7. Static RAM (SRAM) :-
SRAM is faster & volatile than DRAM, but it requires more power & it is more expensive.

9. ROM ROM is Read only Memory.
In this type of memory data is permanently stored.
The information can only be read & new data cannot be written onto this memory.
However, contents of ROM are not lost even when power is turned off, i.e. this is non-volatile memory.
Such memories are also called as ‘field stores’ or ‘permanent stores’.
ROM comes in form of chip. Once information is stored on ROM chip, it cannot be changed or altered.

11. Types of ROM 1) PROM(Programmable Read Only Memory) :-
PROM is memory chip on which data can be written only once.
One program has been written onto PROM, information on PROM cannot be changed.

12. 2) EPROM (Erasable Programmable Read Only Memory) :- It is possible to erase data which ha been previously stored on an EPROM and write new data onto chip.

13. 3) EEPROM(Electrically Erasable Programmable Read Only Memory) :- It is special type of PROM that can be erased by exposing it to an electrical charges.

14. Cache Memory It is very special type of high speed memory.
This type of memory cannot be accessed by user.
The main function of cache memory is to make programs & data available to CPU very fast.
This memory also called as ‘high speed buffer’.

16. Registers Registers are used to retain information temporarily.
These are special memory units, which are not actual parts of main memory but allow efficient movement of information between various units of computer system.
Registers receives information , holds it temporarily and make it available as when required.

18. Secondary Memory/ Secondary Storage Devices
Refers to Various techniques & devices used for storing large amounts of data.
Secondary Storage Devices are non-volatile, i.e. data & programs are permanent , when electric power is turned off data in computer
is not loss.

19. Secondary Storage Devices can be accessed in 2 ways :
1) Sequential or Serial Access :- Data can be accessed only in sequence in which it has been stored. Ex:- Magnetic tape. 2) Random or Direct Access :- Data at any location on storage unit can be accessed directly without follow sequence in which it has been stored. Ex:- Magnetic disk , magnetic drum

20. Sequential/Serial Access Devices :-
Magnetic Tape

21. Magnetic Tape :-
It has same structure like videocassette tape.
Magnetic tape is ribbon(strip) of mylar plastic
& coated with thin layer of iron/magnetic oxide material on one side.
Iron oxide material can be magnetized and data is recorded (encoded) on tape in form of magnetized & non-magnetized spots.

22. Tapes are sometimes called ‘streamers or streaming tapes’.
Tapes come in variety of sizes & formats.
capacity is measured in bytes per inch(bpi).
Most common tape densities are 800 bpi, bpi.

23. Advantages of Magnetic Tape :
High data density & Virtually limited storage.
Easy to handle & portable from one computer to another.
Low in cost.
Limitations of Magnetic Tape :-
Support only Sequential access.
It requires proper storage facilities.

24. Direct/ Random Access Storage Devices :-
Magnetic Disk :-
It is made up of thin metal sheets coated with magnetic oxide.
Types of Magnetic Disk :-
Hard Disk
Floppy Disk

25. Hard Disk :-

26. This is most commonly used secondary storage device.
It contains one or more circular metal platters mounted on central spindle/shaft.
It is covered with magnetic coating.
All the disks in disk pack move at same speed, simultaneously in same direction.
These disks are also called as ‘fixed disks’.
Data are recorded as magnetic spots on coating of disk.
The read/write head is moved in order to position it on a specific track
Hard disk spins about spindle at 3600 rpm to 7200 rpm.
Hard drives has huge storage capacity, typically tens or hundreds of Gigabytes(GB).
Example: Seagate, Samsung.

27. Types of Hard Disks :- 1) Zip Disk :-
A Zip disk is similar in size to a floppy diskette, but thicker.

28. It is basically a “super floppy” but the higher construction tolerances and smaller read/write heads allow the Zip disk to hold more data than a floppy.
The first Zip disks held 100 MB. Later Zip drives could read 250 MB Zips .
An even newer model Zip drive uses 750 MB disks.
We had Zip drives in our previous PCs , but our newer computers don't use this.

29. 2) Disk Packs :-
It consists multiple (two or more) hard disk platters mounted on single central shaft.
All disks revolve together at same speed.
It’s disk drive has separate read/write head for each usable disk surface.
It’s disk drive is of interchangeable type & allows loading/unloading of different disk packs as & when they are to be used.

30. 3) Winchester Disk :-

31. Winchester Disks are permanently enclosed in sealed container.
This are coated with special lubricant to reduce friction with read/write head.
This technology allows for an increase in no. of tracks on disks and higher storage density.
Winchester Disks are fast & highly reliable.
They are extensively in micro computers.

32. Memory Storage Devices:-
These secondary devices has been introduced not only provide storage but also applications like music player.
Types of Memory Storage Devices :-
1) Flash Drive
2) Memory Card

33. Flash Drive (Pen Drive):-
A USB Flash Drive is a portable solid state memory device that plugs into a USB port on your computer.
They have many other names (such as key drive, pocket drive, thumb drive, pen drive).
They have replaced floppy diskettes and Zip disks to carry files around.
These small drives store data on flash memory microchips (a kind of EEPROM).
Flash memory can be erased and re-written a limited number of times (typically many thousands of times).
The storage capacity varies, but anything from 16 MB to over a gigabyte are available.

36. Optical Devices / Discs:-

37. Optical Disk :-
Optical Disk storage system consists of rotating disk coated with thin metal or some material which is highly reflexive.
It uses laser beam technology for recording/ reading of data on disk surface.
Optical Disks are also known as ‘laser disks’ or ‘optical laser beam technology’ because they used laser beam technology for data read/write.

38. Types of Optical Disks :-
(1) CD-ROM(Compact Disk Read Only Memory):-_

39. (2)CD-R (Compact Disc – Recordable):-
The CD-R discs have a layer of dye that is changed by a higher power laser in the drive to record data (the low power reading laser does not change the data).
The CD-R can only have its data surface changed ONCE at each spot (although you can write multiple sessions to one disk until it is full).
After that, it is read-only. CD-Rs can hold 700 MB of data.

40. (3) CD-RW (Compact Disk - Rewritable) :-
The CD-RW discs contain a phase-change material that different power laser beams can read, write, and erase, so these disks can be used many times (but must be erased before re-writing).

41. DVD (Digital Versatile Disc) :-

42. DVD (Digital Versatile Disc) :-
DVD’s are optical storage media similar to CD- ROMs, but with a higher storage capacity.
There are 2 variants of DVD :-
Single layer has storage capacity of 4.7 GB data
dual-layer/double-sided layer holding up to 18 GB of data
Like CD , DVDs also have many types : DVD- R/RW,
DVD +R/RW , DVD- Video, DVD- Audio.

43. Blue-Ray

44. Blue-Ray
Blue-ray is an optical disc format designed to display high definition video and store large amounts of data.
Blue-ray was developed collaboratively by Hitachi, LG, Matsushita (Panasonic), Pioneer, Philips, Samsung, Sharp, Sony, and Thomson. It became the default optical disk standard for HD content and optical data storage.
Blue-ray, also known as Blue-ray Disc (BD) is the name of a new optical disc format that is rapidly replacing DVD. The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data.

45. The format offers more than five times the storage capacity of traditional DVDs and can hold up to 25GB on a single-layer disc and 50GB on a dual-layer disc.
Blue-ray plans to provide a wide range of formats including ROM/R/RW. The following formats are part of the Blue-ray Disc specification:  BD-ROM - read-only format for distribution of HD movies, games, software, etc. BD-R - recordable format for HD video recording and PC data storage. BD-RE - rewritable format for HD video recording and PC data storage.
There's also plans for a BD/DVD hybrid format, which combines Blue-ray and DVD on the same disc so that it can be played in both Blu-ray players and DVD players.