ROM

ROM (read only memory) is a flash memory chip that contains a small amount of non-volatile memory. Non-volatile means that its contents cannot be changed and it retains its memory after the computer is turned off.

History of ROM

Read-only memory were employed as non-volatile storage for programs in most early stored-program computers, such as ENIAC after 1948. ... Most home computers of the 1980s stored a BASIC interpreter or operating system in ROM as other forms of non-volatile storage such as magnetic disk drives were too costly.

Types of ROM

• Programmable read-only memory (PROM), or one-time programmable ROM (OTP), can be written to or programmed via a special device called a PROM programmer. Typically, this device uses high voltages to permanently destroy or create internal links (fuses or antifuses) within the chip. Consequently, a PROM can only be programmed once.

• Erasable programmable read-only memory (EPROM) can be erased by exposure to strong ultravoilet light (typically for 10 minutes or longer), then rewritten with a process that again requires application of higher than usual voltage. Repeated exposure to UV light will eventually wear out an EPROM, but the endurance of most EPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chip packages can often be identified by the prominent quartz "window" which allows UV light to enter. After programming, the window is typically covered with a label to prevent accidental erasure. Some EPROM chips are factory-erased before they are packaged, and include no window; these are effectively PROM.

• Electrically erasable programmable read-only memory (EEPROM) is based on a similar semiconductor structure to EPROM, but allows its entire contents (or selected banks) to be electrically erased, then rewritten electrically, so that they need not be removed from the computer (or camera, MP3 player, etc.). Writing or flashing an EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing to a RAM (nanoseconds in both cases).

Where is the ROM on a computer?

For the computer, the main EEPROM and BIOS is on the computer motherboard.

How does ROM work?

ROM is sustained by a small, long-life battery in the computer. It contains two basic components: the decoder and the or logic gates. In ROM, the decoder receives input in binary form; the output will be the decimal equivalent. The OR gates in ROM use the decoder's decimal output as their input.

ROM performs like a disk array. It contains a grid of rows and columns that are used to turn the system on and off. Every element of the array correlates with a specific memory element on the ROM chip. A diode is used to connect the corresponding elements.

When a request is received, the address input is used to find the specific memory location. The value that is read from the ROM chip should match the contents of the chosen array element.

 

 

 

RAM

Alternatively referred to as main memory, primary memory, or system memory, RAM (random-access memory) is a hardware device that allows information to be stored and retrieved on a computer. RAM is usually associated with DRAM, which is a type of memory module. Because data is accessed randomly instead of sequentially like it is on a CD or hard drive, access times are much faster. However, unlike ROM, RAM is a volatile memory and requires power to keep the data accessible. If the computer is turned off, all data contained in RAM is lost.

History of RAM

The first form of RAM came about in 1947 with the use of the Williams tube. It utilized a CRT (cathode ray tube); the data was stored on the face as electrically charged spots.

The second widely used form of RAM was magnetic-core memory, invented in 1947. Frederick Viehe is credited with much of the work, having filed for several patents relating to the design. Magnetic-core memory works through the use of tiny metal rings and wires connecting to each ring. One bit of data could be stored per ring and accessed at any time.

However, RAM, as we know it today, as solid state memory, was first invented in 1968 by Robert Dennard. Known specifically as dynamic random-access memory, or DRAM, transistors were used to store bits of data.

 

Types of RAM

• DRAM (pronounced DEE-RAM), is widely used as a computer’s main memory. Each DRAM memory cell is made up of a transistor and a capacitor within an integrated circuit, and a data bit is stored in the capacitor. Since transistors always leak a small amount, the capacitors will slowly discharge, causing information stored in it to drain; hence, DRAM has to be refreshed (given a new electronic charge) every few milliseconds to retain data.
• SRAM (pronounced ES-RAM) is made up of four to six transistors. It keeps data in the memory as long as power is supplied to the system unlike DRAM, which has to be refreshed periodically. As such, SRAM is faster but also more expensive, making DRAM the more prevalent memory in computer systems.

What are the common types of DRAM?

• Synchronous DRAM (SDRAM) “synchronizes” the memory speed with CPU clock speed so that the memory controller knows the exact clock cycle when the requested data will be ready. This allows the CPU to perform more instructions at a given time. Typical SDRAM transfers data at speeds up to 133 MHz.
•  Rambus DRAM (RDRAM) takes its name after the company that made it, Rambus. It was popular in the early 2000s and was mainly used for video game devices and graphics cards, with transfer speeds up to 1 GHz.
• Double Data Rate SDRAM (DDR SDRAM) is a type of synchronous memory that nearly doubles the bandwidth of a single data rate (SDR) SDRAM running at the same clock frequency by employing a method  called "double pumping," which allows transfer of data on both the rising and falling edges of the clock signal without any increase in clock frequency.

Computer Memory

In computing, memory refers to a device that is used to store information for immediate use in a computer or related computer hardware device. It typically refers to semiconductor memory, specifically metal–oxide–semiconductor memory, where data is stored within MOS memory cells on a silicon integrated circuit chip.

Types of Computer Memory: Primary and Secondary

Although many types of memory in a computer exist, the most basic distinction is between primary memory, often called system memory, and secondary memory, which is more commonly called storage.

The key difference between primary and secondary memory is speed of access.

• Primary memory includes ROM and RAM, and is located close to the CPU on the computer motherboard, enabling the CPU to read data from primary memory very quickly indeed. It is used to store data that the CPU needs imminently so that it does not have to wait for it to be delivered.
• Secondary memory by contrast, is usually physically located within a separate storage device, such as a hard disk drive or solid state drive (SSD), which is connected to the computer system either directly or over a network. The cost per gigabyte of secondary memory is much lower, but the read and write speeds are significantly slower.

Primary Memory Types: RAM and ROM 

There are two key types of primary memory:

• RAM, or random access memory
• ROM, or read-only memory

Let's look in-depth at both types of memory.

RAM Computer Memory

The acronym RAM stems from the fact that data stored in random access memory can be accessed – as the name suggests – in any random order. Or, put another way, any random bit of data can be accessed just as quickly as any other bit.

The most important things to understand about RAM are that RAM memory is very fast, it can be written to as well as read, it is volatile (so all data stored in RAM memory is lost when it loses power) and, finally, it is very expensive compared to all types of secondary memory in terms of cost per gigabyte. It is because of the relative high cost of RAM compared to secondary memory types that most computer systems use both primary and secondary memory.

Data that is required for imminent processing is moved to RAM where it can be accessed and modified very quickly, so that the CPU is not kept waiting. When the data is no longer required it is shunted out to slower but cheaper secondary memory, and the RAM space that has been freed up is filled with the next chunk of data that is about to be used.

Types of RAM

• DRAM: DRAM stands for Dynamic RAM, and it is the most common type of RAM used in computers. The oldest type is known as single data rate (SDR) DRAM, but newer computers use faster dual data rate (DDR) DRAM. DDR comes in several versions including DDR2 , DDR3, and DDR4, which offer better performance and are more energy efficient than DDR. However different versions are incompatible, so it is not possible to mix DDR2 with DDR3 DRAM in a computer system. DRAM consists of a transistor and a capacitor in each cell.
• SRAM: SRAM stands for Static RAM, and it is a particular type of RAM which is faster than DRAM, but more expensive and bulker, having six transistors in each cell. For those reasons SRAM is generally only used as a data cache within a CPU itself or as RAM in very high-end server systems. A small SRAM cache of the most imminently-needed data can result in significant speed improvements in a system

The difference between DRAM and SRAM is that SRAM is faster than DRAM - perhaps two to three times faster - but more expensive and bulkier. SRAM is usually available in megabytes, while DRAM is purchased in gigabytes.

DRAM uses more energy than SRAM because it constantly needs to be refreshed to maintain data integrity, while SRAM  - though volatile – does not need constant refreshing when it is powered up.

ROM Computer Memory

ROM stands for read-only memory, and the name stems from the fact that while data can be read from this type of computer memory, data cannot normally be written to it. It is a very fast type of computer memory which is usually installed close to the CPU on the motherboard.

ROM is a type of non-volatile memory, which means that the data stored in ROM persists in the memory even when it receives no power – for example when the computer is turned off. In that sense it is similar to secondary memory, which is used for long term storage.

When a computer is turned on, the CPU can begin reading information stored in ROM without the need for drivers or other complex software to help it communicate. The ROM usually contains "bootstrap code" which is the basic set of instructions a computer needs to carry out to become aware of the operating system stored in secondary memory, and to load parts of the operating system into primary memory so that it can start up and become ready to use.

ROM is also used in simpler electronic devices to store firmware which runs as soon as the device is switched on.

Types of ROM

ROM is available in several different types, including PROM, EPROM, and EEPROM.

• PROM PROM stands for Programmable Read-Only Memory, and it is different from true ROM in that while a ROM is programmed (i.e. has data written to it) during the manufacturing process, a PROM is manufactured in an empty state and then programmed later using a PROM programmer or burner.
• EPROM EPROM stands for Erasable Programmable Read-Only Memory, and as the name suggests, data stored in an EPROM can be erased and the EPROM reprogrammed. Erasing an EPROM involves removing it from the computer and exposing it to ultraviolet light before re-burning it.
• EEPROM EEPROM stands for Electrically Erasable Programmable Read-Only Memory, and the distinction between EPROM and EEPROM is that the latter can be erased and written to by the computer system it is installed in. In that sense EEPROM is not strictly read-only. However in many cases the write process is slow, so it is normally only done to update program code such as firmware or BIOS code on an occasional basis

Secondary Memory Types

• Hard Disk Drives

• Solid State Drives
• Optical Drives
• Tape Drives

 

 

Output Devices

There are several output devices that are as follows:

Monitor

This is the most common computer output device. It creates a visual display by the use of which users can view processed data.  Monitors come in various sizes and resolutions.

Common Types of Monitors

• Cathode Ray Tube – this uses phosphorescent dots to generate the pixels that constitute displayed images.
• Flat Panel Screen – this makes use of liquid crystals or plasma to produce output. Light is passed through the liquid crystals in order to generate pixels.

Printer

This device generates a hard copy version of processed data, like documents and photographs. The computer transmits the image data to the printer, which then physically recreates the image, typically on paper.

Types of Printers

• Ink Jet – this kind of printer sprays tiny dots of ink onto a surface to form an image.
• Laser – this type utilises toner drums that roll through magnetized pigment, and then transfers the pigment onto a surface.
• Dot Matrix – dot matrix printers utilise a print head to set images on a surface, using an ink ribbon.

Speakers

speakers are attached to computers to facilitate the output of sound; sound cards are required in the computer for speakers to function. The different kinds of speakers range from simple, two-speaker output devices right the way up to surround-sound multi-channel units.

Headset

This is a combination of speakers and microphone.  It is mostly used by gamers, and is also a great tool for communicating with family and friends over the internet using some VOIP program or other.

Projector

 This is a display device that projects a computer-created image onto another surface: usually some sort of whiteboard or wall. The computer transmits the image data to its video card, which then sends the video image to the projector. It is most often used for presentations, or for viewing videos.

 

Input Devices

There are several input devices that are as follows:

Keyboard

one of the primary input devices used to input data and commands. It has function keys, control keys, arrow keys, keypad and the keyboard itself with the letters, numbers and commands.  Keyboards are connected to the computer through USB or Bluetooth.  A laptop keyboard is more compact than a desktop keyboard to make the laptop smaller and lighter.  Smartphones and tablets use on-screen keyboard to input messages and select commands.

Mouse

It is an input device used to control the cursor and coordinates. It can be wired or wireless.  It allows the user to do the following:

• Move the mouse cursor
• Select
• Scroll
• Open or execute a program
• Drag-and-drop
• Hover
• Perform other functions with the use of additional buttons
• A laptop uses a touchpad as the mouse.  A smartphone and tablet use a touchscreen as primary input device and the user’s finger is used as the mouse.

Microphone

It is an input device that allows users to input audio into their computers. Here are some uses of the microphone:

• Audio for video
• Computer gaming
• Online chatting
• Recording musical instruments
• Recording voice for dictation, singing and podcasts
• Voice recorder
• Voice recognition
• VoIP – Voice over Internet Protocol

Digital Camera

It is an input device that takes pictures digitally. Images are stored as data on memory cards.  It has an LCD screen that allows users to preview and review images.  Digital cameras have become popular over film cameras because of the following features:

• LCD screen – allows users to view the photos and videos immediately
• Storage – can store thousands of pictures
• Picture development – allows users to choose and pick which pictures to develop
• Size – takes up less space and can be easily carried

Scanner

It is an input device that reads an image and converts it into a digital file. A scanner is connected to a computer through USB.  There are different types of scanners:

• Flatbed scanner – uses a flat surface to scan documents
• Sheetfed scanner – like a laser printer where paper is fed into the scanner
• Handheld scanner – the scanner is dragged over the page to be scanned
• Card scanner – for scanning business card

Touch Screen

It is an input device that allows users to interact with a computer using their fingers. It is used widely in laptop monitors, smartphones, tablets, cash registers and information kiosks.  Most common functions of touchscreens are as follows:

• Tap
• Double-tap
• Touch and hold
• Drag
• Swipe
• Pinch

Barcode Reader

It is also known as barcode scanner or point of sale (POS) scanner, is an input device capable of reading barcodes.

Webcam

It is an input device connected to the computer and the internet that captures still picture or motion video.

Biometric Devices

It is an input device used to input biometric data into a computer. Here are the types of biometric devices:

• Face scanner
• Hand scanner
• Finger scanner
• Voice scanner

Stylus

 It is a pen-shaped input device used to write or draw on the screen of a graphic tablet or device. Initially it was just used for graphic tablets and PDAs, but now, it has become popular on mobile devices as a replacement for the user’s fingers.  It’s used for more accurate navigation and to keep oils from user’s fingers off the device screen.

Central Processing Unit (CPU)

The central processing unit (CPU) or processor, is the unit which performs most of the processing inside a computer. It processes all instructions received by software running on the PC and by other hardware components, and acts as a powerful calculator.

The CPU is placed into a specific square-shaped socket found on all motherboards by inserting its metallic connectors or pins found on the underside. Each socket is built with a specific pin layout to support only a specific type of processor.

The CPU is the heart and brain of a computer. It receives data input, executes instructions, and processes information. It communicates with input/output (I/O) devices, which send and receive data to and from the CPU.

The central processing unit (CPU) has two components

Control Unit

The control unit extracts instructions from memory and decodes and executes them.

The control unit acts as an intermediary that decodes the instructions sent to the processor, tells the other units such as the Arithmetic Logic Unit (below) what to do by providing control signals, and then sends back the processed data back to memory.

Arithmetic Logic Unit (ALU)

An arithmetic logic unit (ALU) is a digital circuit inside the processor that handles arithmetic and logical operations by loading data from input registers.

After the control unit provides the ALU with the instruction on the operations that must be performed, the ALU completes them by connecting multiple transistors, and then stores the results in an output register.

The control unit will then move this data to memory.

To function properly, the CPU relies on the system clock, memory, secondary storage, and data and address buses.

Smaller devices like mobile phones, calculators, held gaming systems, and tablets use smaller-sized processors known as ARM CPUs to accommodate their reduced size and space.

Components of a Computer System

Every computer system has the following three basic components:

• Input unit
• Central processing unit
• Output unit

Input Unit

These components help users enter data and commands into a computer system. Data can be in the form of numbers, words, actions, commands, etc. The main function of input devices is to direct commands and data into computers. Computers then use their CPU to process this data and produce output.

Another example of input devices is touch-screens. Users can simply touch these screens without using any other device to enter commands. From smartphones to ATM machines, these input devices are becoming very popular these days.

Central Processing Unit

After receiving data and commands from users, a computer system now has to process it according to the instructions provided. Here, it has to rely on a component called the central processing unit. The CPU further uses these three elements:

Memory Unit

Once a user enters data using input devices, the computer system stores this data in its memory unit. This data will now remain here until other components of CPU process it. The memory unit uses a set of pre-programmed instructions to further transmit this data to other parts of the CPU.

Arithmetic and Logic Unit

This part of the CPU performs arithmetic operations. It does basic mathematical calculations like addition, subtraction, division, multiplication, etc. Further, it can even perform logical functions like the comparison of data.

Control Unit

This unit is the backbone of computers. It is responsible for coordinating tasks between all components of a computer system. The control unit collects data from input units and sends it to processing units depending on its nature. Finally, it also further transmits processed data to output units for users.

Output Unit

The third and final component of a computer system is the output unit. After processing of data, it is converted into a format which humans can understand. After conversion, the output units displays this data to users. Examples of output devices include monitors, screens, printers and speakers. Thus, output units basically reproduce the data formatted by the computer for users’ benefit.