UNITS OF DATA:
HOW CPU PROCESS DATA
The processing of data is performed using following hardware units:
1. Central Processing Unit (CPU) 2. Memory
CPU:
The CPU is the brain of the computer, which executes instructions one after the other. The execution of each instruction is performed with the help of two basic parts:
1. Control unit
2. Arithmetic Logic Unit CONTRUL UNIT (CU):
It controls and co-ordinates the activities of all the units by issuing proper commands. The various responsibilities of the control unit are:
1. Issue propersignals to the memory to fetch the next instruction to be executed.
2. Decode the instruction.
3. Execute the instruction.
4. Issue proper command to ALU, memory, I/O units to get the job done.
INTERCONNECTION OF UNITS
A group of wires connected between various sub-units of a computer to transfer the data/instructions is called PC bus or bus. Two types of PC bus:
1. System bus
a) Data bus b) Address bus c) Control bus 2. I/O bus
a) ISA bus b) PCI bus c) USB bus SYSTEM BUS:
It is used to connect the CPU with RAM and cache memory.
1. Data bus: A group of wires used to transfer the data is called data bus.
2. Address bu: A group of wires exclusively used to transfer the address is called address bus.
3. Control bus: A group of wires used to transfer the control signals is called control bus.
THE I/O BUS:.
It is used to connect all I/O devices with CPU and RAM.
1. ISA bus: ISA (Industry Standard Architecture) I/O bus was also 8 bit and ran at 4.77MHz. It typically runs much slower. One reason is the fact that the ISA bus clock and CPU clock run asynchronously, resulting in many wasted clock cycles.
2. PCI bus: (Peripheral Component Interface), the performance of PCI is much the same as VLB; it too is 32 bits wide and runs and 33MHz, resulting in a bandwidth of 127MB/sec. Two major advantages of PCI over VLB are the support for bus mastering and for Plug and Play.
3. USB: (Universal Serial Bus), helps to convert various devices such as keyboard, mouse, printer very quickly and easily.
MEMORY
Two types:
1. Primary memory 2. Secondary memory
PRIMARY MEMORY/MAIN MEMORY:
Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and data get lost when power is switched off.
It is generally made up of semiconductor device. These memories are not as fast as registers. The data and instruction required to be processed earlier reside in main memory. It is divided into two subcategories RAM and ROM.
Characteristic of Main Memory:
1. These are semiconductor memories.
2. It known as main memory.
3. Usually volatile memory.
4. Data is lost in case power is switch off.
5. It is working memory of the computer.
6. Faster than secondary memories.
7. A computer cannot run without primary memory.
SECONDARY MEMORY:
This type of memory is also known as external memory or non-volatile. It is slower than main memory.
These are used for storing Data/Information permanently.
CPU directly does not access these memories instead they are accessed via input-output routines.
Contents of secondary memories are first transferred to main memory, and then CPU can access it.For example: disk, CD-ROM,DVD etc.
Characteristic of Secondary Memory:
1. These are magnetic and optical memories.
2. It is known as backup memory.
3. It is non-volatile memory.
4. Data is permanently stored even if power is switched off.
5. It is used for storage of the data in the computer.
6. Computer may run without secondary memory.
7. Slower than primary memories.
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.
ADVANTAGE
1. Cache memory is faster than main memory.
2. It consumes less access time as compared to main memory.
3. It stores the program that can be executed within a short period of time.
4. It stores data for temporary use.
DISADVANTAGE:
1. Cache memory has limited capacity.
2. It is very expensive.
RAM (Random Access Memory):
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), Dynamic RAM (DRAM).
ROM (Read Only Memory):
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.