Anatomy of Digital Computer
Block diagram of a computer gives you the pictorial representation of a computer that how it works inside. Or you can say that, in computer's block diagram.
Here is the block diagram of a computer system:
In the above diagram, both control (control unit or CU) and arithmetic & logic unit (ALU) combinely called as Central Processing Unit (CPU).
Let's describe about all the parts as included in the above diagram one by one.
The Processor Unit (CPU)
It is the brain of the computer system.
All major calculation and comparisons are made inside the CPU and it is also responsible for activation and controlling the operation of other unit.
This unit consists of two major components, which are arithmetic logic unit (ALU) and control unit (CU).
Arithmetic Logic Unit (ALU)
Here arithmetic logic unit performs all arithmetic operations such as addition, subtraction, multiplication and division. It also uses logic operation for comparison.
Registers:
It is a small memory unit where only a single bit of data can be stored.
Control Unit (CU)
The control unit of a CPU controls the entire operation of the computer. It also controls all devices such as memory, input/output devices connected to the CPU.
CU fetches instructions from memory, decodes the instruction, interprets the instruction to know what the task are to be performed and sends suitable control signals to the other components to perform for the necessary steps to executes the instruction.
Input/Output Unit
The input/output unit consists of devices used to transmit information between the external world and computer memory.
The information fed through the input unit is stored in computer's memory for processing and the final result stored in memory can be recorded or display on the output medium.
Memory unit is an essential component of a digital computer. It is where all data intermediate and find results are stored.
The data read from the main storage or an input unit are transferred to the computer's memory where they are available for processing.
This memory unit is used to hold the instructions to be executed and data to be processes.
Disk Storage Unit
Data and instruction enters into a computer system through input device have to stored inside the computer before actual processing start.
Two types of storage unit are primary and secondary storage unit.
Primary Storage Unit
Primary memory has direct link with input unit and output unit. It stores the input data, calculation result.
Secondary Storage Unit
The primary storage is not able to store data permanently for future use. So some other types of storage technology is required to store the data permanently for long time, it is called secondary or auxiliary storage.
Communication Unit
Hardware devices that support data transmission and reception across a telecommunication system are called communication devices. These devices includes : modem, multiplexer, network interfaced card and so on.communication devices enables computers to communicate in the network.
Computer Architecture mean?
Computer architecture is a specification detailing how a set of software and hardware technology standards interact to form a computer system or platform. In short, computer architecture refers to how a computer system is designed and what technologies it is compatible with.
As with other contexts and meanings of the word architecture, computer architecture is likened to the art of determining the needs of the user/system/technology, and creating a logical design and standards based on those requirements.
Computer Architecture
A very good example of computer architecture is von Neumann architecture, which is still used by most types of computers today. This was proposed by the mathematician John von Neumann in 1945. It describes the design of an electronic computer with its CPU, which includes the arithmetic logic unit, control unit, registers, memory for data and instructions, an input/output interface and external storage functions.
There are three categories of computer architecture:
- System Design: This includes all hardware components in the system, including data processors aside from the CPU, such as the graphics processing unit and direct memory access. It also includes memory controllers, data paths and miscellaneous things like multiprocessing and virtualization.
- Instruction Set Architecture (ISA): This is the embedded programming language of the central processing unit. It defines the CPU's functions and capabilities based on what programming it can perform or process. This includes the word size, processor register types, memory addressing modes, data formats and the instruction set that programmers use.
- Microarchitecture: Otherwise known as computer organization, this type of architecture defines the data paths, data processing and storage elements, as well as how they should be implemented in the ISA.
Von Neumann Architecture
Von Neumann architecture was first published by John von Neumann in 1945.
His computer architecture design consists of a Control Unit, Arithmetic Logic Unit(ALU) , Memory Unit, Registers and Inputs/Outputs.
Von Neumann architecture is based on the stored-program computer concept, where instruction data and program data are stored in the same memory. This design is still used in most computers produced today.
MAR
|
Memory Address Register
|
Holds the memory location of data that needs to be accessed
|
MDR
| Memory Data Register |
Holds data that is being transferred to or from memory
|
AC
| Accumulator |
Where intermediate arithmetic and logic results are stored
|
PC
|
Program Counter
|
Contains the address of the next instruction to be executed
|
CIR
|
Current Instruction Register
|
Contains the current instruction during processing
|
Central Processing Unit (CPU)
The Central Processing Unit(CPU) is the electronic circuit responsible for executing the instructions of a computer program.
It is sometimes referred to as the microprocessor or processor.
The CPU contains the ALU, CU and a variety of registers.
Registers
Registers are high speed storage areas in the CPU. All data must be stored in a registers before it can be processed.
The ALU allows arithmetic (add, subtract etc) and logic (AND, OR, NOT etc) operations to be carried out.Arithmetic and Logic Unit (ALU)
Control Unit (CU)
The control unit controls the operation of the computer’s ALU, memory and Input/Output devices, telling them how to respond to the program instructions it has just read and interpreted from the memory unit.
The control unit also provides the timing and control signals required by other computer components.
Buses
Buses are the means by which data is transmitted from one part of a computer to another, connecting all major internal components to the CPU and memory.
A standard CPU system bus is comprised of a control bus, data bus and address bus.
| Address Bus |
Carries the addresses of data (but not the data) between the processor and memory
|
Data Bus
|
Carries data between the processor, the memory unit and the input/output devices
|
Control Bus
|
Carries control signals/commands from the CPU (and status signals from other devices) in order to control and coordinate all the activities within the computer
|
Memory Unit
The memory unit consists of RAM, sometimes referred to as primary or main memory. Unlike a hard drive (secondary memory), this memory is fast and also directly accessible by the CPU.
The address will uniquely identify every location in the memory.
Loading data from permanent memory (hard drive), into the faster and directly accessible temporary memory (RAM), allows the CPU to operate much quicker.
Harvard Architecture mean?
The Harvard architecture is a term for a computer system that contains two separate areas for commands or instructions and data. In the Harvard architecture, the media, format and nature of the two different parts of the system may be different, as the two systems are represented by two separate structures.
Some examples of Harvard architectures involve early computer systems where programming input could be in one media, for example, punch cards, and stored data could be in another media, for example, on tape. More modern computers may have modern CPU processes for both systems, but separate them in a hardware design.
The Harvard architecture, with its strict separation of code and data processes, can be contrasted with a modified Harvard architecture, which may combine some features of code and data systems while preserving separation in others. One example is the use of two caches, with one common address space. It can also be contrasted with a von Neumann architecture, named for John von Neumann, which does not focus on separating input from data.
Anatomy of digital computer
Block diagram of a computer gives you the pictorial representation of a computer that how it works inside. Or you can say that, in computer's block diagram, we will see how computer works from feeding the data to getting the result.
Here is the block diagram of a computer system:
I
In the above diagram, both control (control unit or CU) and arithmetic & logic unit (ALU) combinely called as Central Processing Unit(CPU).
Let's describe about all the parts as included in the above diagram one by one.
The Processor Unit (CPU)
It is the brain of the computer system.
All major calculation and comparisons are made inside the CPU and it is also responsible for activation and controlling the operation of other unit.
This unit consists of two major components, which are arithmetic logic unit (ALU) and control unit (CU).
Arithmetic Logic Unit (ALU)
Here arithmetic logic unit performs all arithmetic operations such as addition, subtraction, multiplication and division. It also uses logic operation for comparison.
Registers:
It is a small memory unit where only a single bit of data can be stored.
Control Unit (CU)
The control unit of a CPU controls the entire operation of the computer. It also controls all devices such as memory, input/output devices connected to the CPU.
CU fetches instructions from memory, decodes the instruction, interprets the instruction to know what the task are to be performed and sends suitable control signals to the other components to perform for the necessary steps to executes the instruction.
Input/Output Unit
The input/output unit consists of devices used to transmit information between the external world and computer memory.
The information fed through the input unit is stored in computer's memory for processing and the final result stored in memory can be recorded or display on the output medium.
Memory Unit
Memory unit is an essential component of a digital computer. It is where all data intermediate and find results are stored.
The data read from the main storage or an input unit are transferred to the computer memory, where they are available for processing.
This memory unit is used to hold the instructions to be executed and data to be processes.
Disk Storage Unit
Data and instruction enters into a computer system through input devices have to stored inside the computer before actual processing start.
Two types of storage unit are primary and secondary storage unit.
Primary Storage Unit
Primary memory has direct link with input unit and output unit. It stores the input data, calculation result.
Secondary Storage Unit
The primary storage is not able to store data permanently for future use. So some other types of storage technology is required to store the data permanently for long time, it is called secondary or auxiliary storage.
Communication Unit
Hardware devices that support data transmission and reception across a telecommunication system are called communication devices. These devices includes : modem, multiplexer, network interfaced card and so on.communication devices enables computers to communicate in the network.
Computer memory/storage:
Primary Storage
• Also known as main memory, Main memory is directly or indirectly connected to the central processing unit via a memory bus.
• The CPU continuously reads instructions stored there and executes them as required.
• Examples:
– RAM (Random Access Memory)
– ROM (Read Only Memory)
– Cache
RAM
• It is called Random Access Memory because any of the data in RAM can be accessed just as fast as any of the other data.
• There are two types of RAM:
– DRAM (Dynamic Random Access Memory) and SRAM ( Static Random Access Memory)
Static RAM
• Faster • More expensive • More power consumption • does not need to be refreshed
Dynamic RAM
• Slower • Less expensive • Less power consumption • needs to be refreshed thousands of times per second– SRAM (Static Random Access Memory)
ROM
• This memory is used as the computer begins to boot up.
• Small programs called firmware are often stored in ROM chips on hardware devices (like a BIOS chip), and they contain instructions the computer can use in performing some of the most basic operations required to operate hardware devices.
• ROM memory cannot be easily or quickly overwritten or modified.
Cache
• Cache is a high-speed access area that can be either a reserved section of main memory or a storage device.
• Most computers today come with L3 cache or L2 cache, while older computers included only L1 cache.
Secondary Storage
• It is not directly accessible by the CPU. • Computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage.
• Example: –
Hard disk
The hard disk drive is the main, and usually largest, data storage device in a computer.
• It can store anywhere from 160 gigabytes to 2 terabytes.
• Hard disk speed is the speed at which content can be read and written on a hard disk.
• A hard disk unit comes with a set rotation speed varying from 4500 to 7200 rpm.
• Disk access time is measured in milliseconds
The types of Hard Disk are:
i) Internal hard disk: features are: No portable, Less expensive, Fast speed, big size as compare to external.
ii) External Hard disk : features are: Portability, More expensive, Slow speed, Small size
-Optical Disc
• Optical disc is any storage media that holds content in digital format and is read using a laser assembly is considered optical media.
• The most common types of optical media are
– Blu-ray (BD)
– Compact Disc (CD)
– Digital Versatile Disc (DVD)
-Magnetic Tape
• A magnetically coated strip of plastic on which data can be encoded.
• Tapes for computers are similar to tapes used to store music.
• Tape is much less expensive than other storage mediums but commonly a much slower solution that is commonly used for backup.
Off-line Storage
• Examples:
– Floppy Disk
• A soft magnetic disk.
• Floppy disks are portable.
• Floppy disks are slower to access than hard disks and have less storage capacity, but they are much less expensive.
• Can store data up to 1.44MB.
• Two common sizes: 5 ¼” and 3 ½”.
– Zip diskette
Hardware data storage device developed by Iomega that functions like a Standard 1.44" floppy drive.
• Capable to hold up to 100 MB of data or 250 MB of data on new drives.
• Now it less popular as users needed larger storage capabilities.
– USB Flash drive
A small, portable flash memory card that plugs into a computer’s USB port and functions as a portable hard drive.
• Flash drives are available in sizes such as 256MB, 512MB, 1GB, 5GB, and 16GB and are an easy way to transfer and store information.
– Memory card
• An electronic flash memory storage disk commonly used in consumer electronic devices such as digital cameras, MP3 players, mobile phones, and other small portable devices.
• Memory cards are usually read by connecting the device containing the card to your computer, or by using a USB card reader.
SIMM (Single In-line Memory Module) and DIMM (Dual In-line Memory Module)
Theses two terms (SIMM and DIMM) refer to a way series of dynamic random access memory integrated circuits modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers.
SIMM
Short for Single In-line Memory Module, SIMM is a circuit board that holds six to nine memory chips per board, the ninth chip usually an error checking chip (parity/non parity) and were commonly used with Intel Pentium or Pentium compatible motherboards. SIMMs are rarely used today and have been widely replaced by DIMMs. SIMMs are available in two flavors: 30 pin and 72 pin. 30-pin SIMMs are the older standard, and were popular on third and fourth generation motherboards. 72-pin SIMMs are used on fourth, fifth and sixth generation PCs.
DIMM
Short for Dual In-line Memory Module, DIMM is a circuit board that holds memory chips. DIMMs have a 64-bit path because of the Pentium Processor requirements. Because of the new bit path, DIMMs can be installed one at a time, unlike SIMMs on a Pentium that would require two to be added. Below is an example image of a 512MB DIMM memory stick.
SO-DIMM is short for Small Outline DIMM and is available as a 72-pin and 144-pin configuration.
SO-DIMMs are commonly utilized in laptop computers.
Some of the advantages DIMMs have over SIMMs:
§ DIMMs have separate contacts on each side of the board, thereby providing twice as
much data as a single SIMM.
§ The command address and control signals are buffered on the DIMMs. With heavy
memory requirements this will reduce the loading effort of the memory.
1.4.2 Advantage of ICs
· In consumer electronics, ICs have made possible the development of many new products, including personal calculators and computers, digital watches, and video games.
· They have also been used to improve or lower the cost of many existing products, such as appliances, televisions, radios, and high-fidelity equipment.
· The logic and arithmetic functions of a small computer can now be performed on a single VLSI chip called a microprocessor.
· Complete logic, arithmetic, and memory functions of a small computer can be packaged on a single printed circuit board, or even on a single chip.
1.4.3 Scale of integration – SSI, MSI, LSI, VLSI
During 1959 two different scientists invented IC’s. Jack Kilby from Texas Instruments made his first germanium IC during 1959 and Robert Noyce made his first silicon IC during the same year. But ICs were not the same since the day of their invention; they have evolved a long way. Integrated circuits are often classified by the number of transistors and other electronic components they contain:
· SSI (small-scale integration): Up to 100 electronic components per chip
· MSI (medium-scale integration): From 100 to 3,000 electronic components per chip
· LSI (large-scale integration): From 3,000 to 100,000 electronic components per chip
· VLSI (very large-scale integration): From 100,000 to 1,000,000 electronic components per chip
· ULSI (ultra large-scale integration): More than 1 million electronic components per chip
0 Comments