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ANDRÉS PUENTES
FATIMA ALYLI
SALVADOR BARDAWIL
SUSANN HERNÁNDEZ

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Trackball mouse

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Any kind of device used to send data from a computer to another external device or user.

1- Projectors - They´re connected to the computer by a program or a cable. With light, it reflects the images that are shown in the computer on a wall.
2- Speakers- Are connected by a cable or bluetooth. The sounds that are played in the computer, sound in the speakers making the noise louder.
3- Printers- Are connected by cable or by bluetooth. Documents are send by the computer to the printer and prints the document.

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A memory is just like a human brain. It is used to store data and instruction. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts. Each part is called a cell. Each location or cell has a unique address which varies from zero to memory size minus one.

For example if computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory location. The address of these locations varies from 0 to 65535.

Memory is primarily of two types

Characteristics of Memory Hierarchy are following when we go from top to bottom.

Capacity in terms of storage increases.

Cost per bit of storage decreases.

Frequency of access of the memory by the CPU decreases.

Access time by the CPU increases.

RAM

A RAM constitutes the internal memory of the CPU for storing data, program and program result. It is read/write memory. It is called random access memory (RAM).

Since access time in RAM is independent of the address to the word that is, each storage location inside the memory is as easy to reach as other location & takes the same amount of time. We can reach into the memory at random & extremely fast but can also be quite expensive.

RAM is volatile, i.e. data stored in it is lost when we switch off the computer or if there is a power failure. Hence, a backup uninterruptible power system (UPS) is often used with computers. RAM is small, both in terms of its physical size and in the amount of data it can hold.

RAM is of two types

Static RAM (SRAM)

The word static indicates that the memory retains its contents as long as power remains applied. However, data is lost when the power gets down due to volatile nature. SRAM chips use a matrix of 6-transistors and no capacitors. Transistors do not require power to prevent leakage, so SRAM need not have to be refreshed on a regular basis.

Because of the extra space in the matrix, SRAM uses more chips than DRAM for the same amount of storage space, thus making the manufacturing costs higher.

Static RAM is used as cache memory needs to be very fast and small.

Dynamic RAM (DRAM)

DRAM, unlike SRAM, must be continually refreshed in order for it to maintain the data. This is done by placing the memory on a refresh circuit that rewrites the data several hundred times per second. DRAM is used for most system memory because it is cheap and small. All DRAMs are made up of memory cells. These cells are composed of one capacitor and one transistor.

ROM

ROM stands for Read Only Memory. The memory from which we can only read but cannot write on it. This type of memory is non-volatile. The information is stored permanently in such memories during manufacture.

A ROM, stores such instruction as are required to start computer when electricity is first turned on, this operation is referred to as bootstrap. ROM chip are not only used in the computer but also in other electronic items like washing machine and microwave oven.

Following are the various types of ROM −

MROM (Masked ROM)

The very first ROMs were hard-wired devices that contained a pre-programmed set of data or instructions. These kind of ROMs are known as masked ROMs. It is inexpensive ROM.

PROM (Programmable Read Only Memory)

PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM programmer. Inside the PROM chip there are small fuses which are burnt open during programming. It can be programmed only once and is not erasable.

EPROM (Erasable and Programmable Read Only Memory)

The EPROM can be erased by exposing it to ultra-violet light for a duration of upto 40 minutes. Usually, an EPROM eraser achieves this function. During programming an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultra-violet light is passed through a quartz crystal window (lid). This exposure to ultra-violet light dissipates the charge. During normal use the quartz lid is sealed with a sticker.

EEPROM (Electrically Erasable and Programmable Read Only Memory)

The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. Both erasing and programming take about 4 to 10 ms (millisecond). In EEPROM, any location can be selectively erased and programmed. EEPROMs can be erased one byte at a time, rather than erasing the entire chip. Hence, the process of re-programming is flexible but slow.

Serial Access Memory

Sequential access means the system must search the storage device from the beginning of the memory address until it finds the required piece of data. Memory device which supports such access is called a Sequential Access Memory or Serial Access Memory. Magnetic tape is an example of serial access memory.

Direct Access Memory

Direct access memory or Random Access Memory, refers to conditions in which a system can go directly to the information that the user wants. Memory device which supports such access is called a Direct Access Memory. Magnetic disks, optical disks are examples of direct access memory.

Cache Memory

Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory. It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs, are transferred from disk to cache memory by operating system, from where CPU can access them.

Advantages

Cache memory is faster than main memory.

It consumes less access time as compared to main memory.

It stores the program that can be executed within a short period of time.

It stores data for temporary use.

Disadvantages

Cache memory has limited capacity.

It is very expensive.

Virtual memory is a technique that allows the execution of processes which are not completely available in memory. The main visible advantage of this scheme is that programs can be larger than physical memory. Virtual memory is the separation of user logical memory from physical memory.

This separation allows an extremely large virtual memory to be provided for programmers when only a smaller physical memory is available. Following are the situations, when entire program is not required to be loaded fully in main memory.

User written error handling routines are used only when an error occurred in the data or computation.

Certain options and features of a program may be used rarely.

Many tables are assigned a fixed amount of address space even though only a small amount of the table is actually used.

The ability to execute a program that is only partially in memory would counter many benefits.

Less number of I/O would be needed to load or swap each user program into memory.

A program would no longer be constrained by the amount of physical memory that is available.

Each user program could take less physical memory, more programs could be run the same time, with a corresponding increase in CPU utilization and throughput.

Auxiliary Memory

Auxiliary memory is much larger in size than main memory but is slower. It normally stores system programs, instruction and data files. It is also known as secondary memory. It can also be used as an overflow/virtual memory in case the main memory capacity has been exceeded. Secondary memories cannot be accessed directly by a processor. First the data/information of auxiliary memory is transferred to the main memory and then that information can be accessed by the CPU. Characteristics of Auxiliary Memory are following −

Non-volatile memory − Data is not lost when power is cut off.

Reusable − The data stays in the secondary storage on permanent basis until it is not overwritten or deleted by the user.

Reliable − Data in secondary storage is safe because of high physical stability of secondary storage device.

Convenience − With the help of a computer software, authorised people can locate and access the data quickly.

Capacity − Secondary storage can store large volumes of data in sets of multiple disks.

Cost − It is much lesser expensive to store data on a tape or disk than primary memory.

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A memory is just like a human brain. It is used to store data and instruction. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. The memory is divided into large number of small parts. Each part is called a cell.

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Alternatively referred to as digital storage, , storage media, or storage medium, a storage device is any hardware capable of holding information either temporarily or permanently. The picture shows an example of a Drobo, an external secondary storage device.

There are two types of storage devices used with computers: a primary storage device, such as RAM, and a secondary storage device, like a hard drive. Secondary storage can be removable, internal, or external storage.

Examples of computer storage

Magnetic storage devices

Today, magnetic storage is one of the most common types of storage used with computers and is the technology that many computer hard drives use.

Optical storage devices

Another common storage is optical storage, which uses lasers and lights as its method of reading and writing data.

Flash memory devices

Flash memory has started to replace magnetic media as it becomes cheaper as it is the more efficient and reliable solution.

Online and cloud

Storing data online and in cloud storage is becoming popular as people need to access their data from more than one device.

Paper storage

Early computers had no method of using any of the above technologies for storing information and had to rely on paper. Today, these forms of storage are rarely used or found. In the picture to the right is an example of a woman entering data to a punch card using a punch card machine.

Why is storage needed in a computer?

Without a storage device, a computer can not save or remember any settings or information and would be considered a dumb terminal.

Although a computer can run with no storage device, it would only be able to view information unless it was connected to another computer that had storage capabilities. Even a task such as browsing the Internet requires information to be stored on your computer.

Why so many different storage devices?

As computers advance so do the requirements for storage space and the technologies used to store data. Because people need more and more space, want it faster, cheaper, and want to take it with them new technologies have to be invented. When new storage devices are designed, as people upgrade to those new devices the older devices are no longer needed and stop being used.

For example, when punch cards were first used in early computers the magnetic media used for floppy disks was not available. After floppy diskettes had been released, they were replaced by CD-ROM drives, which were replaced by DVD drives, which have been replaced by flash drives. The first hard disk drive from IBM cost $50,000, was only 5 MB, was big, and cumbersome. Today, we have smartphones that have hundreds of times the capacity at a much smaller price that we can carry with us in our pocket.

Each advancement of storage devices gives a computer the ability to store more data, save data faster, and access the saved data faster.

What is a storage location?

When saving anything on a computer, it may ask you for a storage location, which is the area in which you would like to save the information. By default, most information is saved to your computer hard drive. If you want to move the information to another computer, save it to a removable storage device such as a flash drive.

What storage devices are used today?

Most of the storage devices mentioned earlier are no longer used with today's computers which primarily use a hard disk drive or SSD to store information and have the options for USB flash drives and access to cloud storage. Desktop computers with disc drives typically use a disc drive that is capable of reading CD's and DVD's and writing CD-R and other recordable discs.

What storage device has the largest capacity?

For most computers, the largest storage device is the hard drive or SSD. However, networked computers may also have access to larger storage with large tape drives, cloud computing, or NAS devices. Below is a list of storage devices from the smallest capacity to the largest capacity.

Note: Many storage devices have been available in many different capacities. For example, over the evolution of the hard drive, there have been drives that range from the first hard drive of 5 MB to hard drives today that are several terabytes in size. Therefore, the below list is only meant to give a general understanding of the size differences between each storage devices today and is not an exact list. For example, the earliest hard drives are smaller than a CD.

Are storage devices input and output devices?

No. Although these devices do send and receive information, they are not considered an input device or output device. It is more proper to refer to any device capable of storing and reading information from a storage device, disk, disc, or a drive.

How do you access storage devices?

To access a storage device on your computer depends on the operating system your computer is using and how it's being used. For example, with Microsoft Windows, you can use a file manager to access the files on any storage device. Microsoft Windows uses Explorer as its default file manager. With Apple computers, Finder is considered the default file manager.

CD terms, Cloud, Floppy drive terms, Hard drive terms, Hardware terms, I/O Device, Memory terms, Permanent storage, SAN, Non-volatile, Tape terms

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Alternatively referred to as digital storage, , storage media, or storage medium, a storage device is any hardware capable of holding information either temporarily or permanently. The picture shows an example of a Drobo, an external secondary storage device.

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An input device is any Hardware device that sends data to a computer. A good example is a Logitech

1.Trackball mouse , it allows an individual to control a pointer in a graphical user interface.

2. Audio conversion device
They are designed to convert audio of various formats into a digital format for use on a computer.

3. Business card reader
allows a user to scan business cards into their computer for digital storage.

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http://www.definitions.net/definition/memory

http://www.tutorialspoint.com/computer_logical_organization/memory_devices.htm

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Is any hardware capable of holding information either temporarily or permanently.
RAM and Hard Drive.

Ex1: Hard Disc:
A small hard drive typically has only one platter, but each side of it has a magnetic coating. Bigger drives have a series of platters stacked on a central spindle, with a small gap in between them.

Ex2: DVD's
Up to 133 minutes of high-resolution video, in letterbox or pan-and-scan format, with 720 dots of horizontal resolution (The video compression ratio is typically 40:1 using MPEG-2 compression.)

Ex3: CD's
A CD can store up to 74 minutes of music.To fit more than 783 megabytes (MB) onto a disc only 4.8 inches (12 cm) in diameter requires that the individual bytes be very small.

http://www.computerhope.com/jargon/s/stordevi.htm

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					What does Memory mean? 
				
			
		

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					What does Memory mean? 
				
			
		

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The part of a computer that stores variable executable code or data (RAM) or unalterable executable code or default data (ROM).

Internal Memory − cache memory and primary/main memory

External Memory − magnetic disk / optical disk etc.

RAM − A RAM constitutes the internal memory of the CPU for storing data, program and program result.

ROM − A ROM, stores such instruction as are required to start computer when electricity is first turned on.

PROM − PROM is read-only memory that can be modified only once by a user.