Type of memories

Memory and I/O in computers

Type of memories

 Primary memory

 Secondary memory

Difference

Property Primary Secondary

Storage capacity

Small Large

Access time Fast low

Cost high low

Volatility volatile Non-volatile

Access Random access Sequential access and Direct access

Primary memory

 Every computer has a temporary storage built into the computer hardware

 It stores instructions and data of a program mainly when the program is being executed by the CPU.

 This temporary storage is known as main memory, primary storage, or simply memory

Random Access Memory (RAM)

 Primary storage of a computer is often referred to as RAM because of its random access capability

 RAM chips are volatile memory

 A computer’s motherboard is designed in a manner that the

memory capacity can be enhanced by adding more memory chips

Read Only Memory (ROM)

 ROM a non-volatile memory chip

 Data stored in a ROM can only be read and used – they cannot be changed

 ROMs are mainly used to store programs and data, which do not change and are frequently used. For example, system boot program

Types of ROMs

 Manufacturer-programmed- Data is burnt by the

manufacturer of the electronic equipment in which it is used.

 User-programmed/programmable (PROM)- The user can load and store “read-only” programs and data in it.

 Erasable PROM (EPROM)- The user can erase

information stored in it and the chip can be reprogrammed to store new information.

 Ultra Violet EPROM (UVEPROM)- A type of EPROM

chip in which the stored information is erased by exposing the chip for some time to ultra-violet light.

 Electrically EPROM (EEPROM) or Flash memory- A type of EPROM chip in which the stored information is erased by using high voltage electric pulses.

Cache Memory

 It is commonly used for minimizing the memory-processor speed mismatch.

 It is an extremely fast, small memory between CPU and main memory whose access time is closer to the processing speed of the CPU.

 It is used to temporarily store very active data and instructions during processing

CPU Registers



Commonly used as temporary storage in a processor.



Faster and more convenient than main memory.



More registers can help speed up complex calculations.



There are many different kinds of registers.

Memory Hierarchy

Limitations of Primary Storage

 Limited capacity because the cost per bit of storage is high

 Volatile - data stored in it is lost when the electric power is turned off or interrupted

Secondary Storage

 Used in a computer system to

overcome the limitations of primary storage

 Has virtually unlimited capacity

because the cost of storage is very low

 Has an operating speed far slower than that of the primary storage

 Used to store large volumes of data on a permanent basis

 Also known as auxiliary memory

Sequential-access Storage Devices

 Arrival at the desired storage location may be preceded by sequencing through other locations

 Data can only be retrieved in the same sequence in which it is stored

 Access time varies according to the storage location of the information being accessed

 Suitable for sequential processing applications where most, if not all, of the data records need to be processed one after

another

 Magnetic tape is a typical example of such a storage device

Direct-access Storage Devices

 Devices where any storage location may be selected and accessed at random

 Permits access to individual information in a more direct or immediate manner

 Approximately equal access time is required for accessing information from any storage location

 Suitable for direct processing applications such as on-line ticket booking systems, on-line banking systems

 Magnetic disks are typical examples of such a storage device.

Optical Disks

• Optical secondary storage devices: A common optical disk is Compact disc read-only memory (CD-ROM) with a storage capacity is 740 MB.

• In CD-ROM data can not be modified once it has been recorded, the disk is “read-only”.

• A CD burner or CD recorder is a device that can record data to a compact disk.

• There are two types of CD’s

• CD-recordable {CD-R}

• CD-rewritable {CD-RW}

Digital video disc

• Digital video disc (DVD): DVD is a five-inch diameter CD- ROM looks like a CD but can store about 135 minutes of digital video or several gigabytes of data.

• Capacity of CD is about 740 MB data, single-sided DVD can hold 4.7 GB data and the capacity of double sided DVD is 9.4 GB.

Solid state secondary storage devices

 Solid state secondary storage devices:

 Store data in memory chips rather than magnetic or optical media.

 SSD’s have few moving parts, so they are less breakable than hard disk drives.

 A Universal Serial Bus (USB) flash drive is one example of commonly used SSD.

 USB flash drives are external to the computer and are removable and rewritable.

Input Device

 This unit contains devices with the help of which we enter data into the computer.

 This unit creates a link between the user and the computer.

 The input devices translate the information into a form understandable by the computer

Various input devices

 Keyboard

 Mouse

 Joy Stick

 Light pen

 Scanner

 Microphone

 Optical Character Reader (OCR)

 Bar Code Reader

Keyboard

 Keyboard is the most common and very popular input device which helps to input data to the computer.

 The layout of the keyboard is like that of traditional typewriter, although

there are some additional keys

provided for performing additional functions.

 Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available

Mouse

 Mouse is the most popular pointing device.

 It sends signals to the CPU when the mouse buttons are pressed.

 Generally, it has two buttons called the left and the right button and a wheel is present between the

buttons.

 A mouse can be used to control the position of the cursor on the screen, but it cannot be used to enter text into the computer.

Light pen

 Light pen is a pointing device similar to a pen.

 It is used to select a displayed menu item or draw pictures on the monitor screen.

 When the tip of a light pen is moved over the monitor screen, its photocell sensing

element detects the screen location and sends the corresponding signal to the CPU.

Scanner

 Scanner is an input device, which

works more like a photocopy machine.

 It is used when some information is available on paper and it is to be

transferred to the hard disk of the computer for further manipulation.

 Scanner captures images from the

source which are then converted into a digital form that can be stored on the disk

Output Devices

 An output device consists of devices with the help of which we get the information from the computer.

 This unit is a link between the computer and the users.

 Output devices translate the computer's output into a form understandable by the users.

Commonly used Output Devices

 Monitor

 Printer

Monitor

 Monitors, commonly called as Visual Display Unit (VDU), are the main

output device of a computer.

 It forms images from tiny dots, called pixels that are arranged in a rectangular form.

 The sharpness of the image depends upon the number of pixels.

Printer

 Printer is an output device, which is used to print information on paper.

 Some commonly used printers:

 Dot Matrix

 Laser

 Inkjet

Purchasing a computer

 Four Steps To Purchase a Computer

1. Purpose: What type of computer is needed?

2. Cost: How much money can I spend?

3. Hardware Types: What kind of hardware best serves my needs?

4. Software Types: Which application softwares serves my needs?

Factors

• Cost

• CPU Speed

• Memory Size and Speed

• Portability

• Single/Multi-User System

• Personal or Business

Purchasing a computer

 Monitor-

 Size

 Resolution

• Operating System-

• Windows 10

• Linux

• Mac

Purchasing a computer

 RAM-

 Speed

 Capacity

• Hard Drive-

• Capacity

• CPU-

• Speed

• Core