Short questions Class 11 Computer Science notes Chapter 2
Q.2 i) What is computer memory?
“The storage space in computer where data is to be processed and instructions required for processing are stored”.
It is any device that is capable of storing information temporarily or permanently. It is just like a human brain. The computer memory is divided into large number of small parts called cells. Each location or cell has a unique address which varies from zero to memory size minus one. For example, if memory size is ‘n’ then the cell address ranges to ‘n-1’.
Memory is of three types:
– Cache memory
– Primary memory / Main memory
– Secondary memory
Cache memory is the fastest memory. It acts as a buffer between the CPU and main memory. Primary memory is the working area of the computer. It stores data temporarily.
Secondary memory is the permanent storage area of the computer.
Q.2 ii) Define bit, byte and memory word.
A bit is a short form of ‘binary digit’.
“A bit is a single and smallest amount of computer memory.”
A binary digit is logical 0 or 1 representing a passive or active of the component in an electric circuit.
“A group of 8 bits is called byte.”
A byte is the smallest unit which can represent a data item or a character.
“A group of a fixed number of bits processed as a unit which varies from computer to computer.”
Modern computers have a size of 16, 32 or 64 bits.
Q.2 iii) What is the importance of cache memory in a computer?
Cache memory is a very high speed semiconductor memory which can speed up CPU. It is extremely important part of modern computers. Computers are faster now day because they have fastest memory transfer rate that competes to the speed of microprocessor which makes calculations. Microprocessor can only perform fast calculations when the data is fed quickly. If the processor doesn’t have any data to calculate on a cycle, the cycle is missed and the calculation will not occur until the next cycle, which reduces the speed of microprocessor. The job of the cache memory is to eliminate as many wasted cycles as possible.
The advantages of cache memory are as follows:
- 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.
The disadvantages of cache memory are as follows:
- Cache memory has limited capacity.
- It is very expensive.
Q.2 iv) Give some uses of secondary memory.
Secondary 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 memory are first transferred to main memory and them CPU can access it. For example, disk, CD-ROM, DVD etc.
Read more: KPK Class 11 Computer Science notes Chapter 1 (Introduction to computer system)
Uses of secondary memory:
- The secondary memory has huge space for data storage.
- The secondary memory is used for long-term storage of programs and data in computer.
- CPU cannot access it directly so it is less accessible to viruses.
Q.2 v) What is the role of registers in computer?
Register is a special high speed storage area within the CPU. It is has a major role in memory of computer because all data must be represented in a register before it can be processed. For example, it two numbers are added, both numbers must be in registers and the result is also placed in a register.
The register can also contain the address of a memory location where data is stored rather than the actual data itself.
The number of registers that a CPU has and the size of each register determine the power and speed of a CPU. For example, a 32-bit CPU is one in which each register is 32-bits wide. Therefore, each CPU instruction can manipulate 32 bits of data.
Some of the main registers in CPU are as follows:
Accumulator register (AC): It is located in ALU and it is used to store the results of arithmetic and logic unit operations.
Status register: It is used to indicate certain condition during CPU operation.
Instruction Register (IR): It holds the instruction which has to be executed next.
Program Counter (PC): It is also called instruction pointer register. It is used store the address of next instruction which is to be fetched for execution.
Buffer Register : This register is used to hold the contents of data or instruction read or written in memory.
Q.2 vi) Differentiate between DRAM and SRAM.
The difference between SRAM and DRAM is as follows:
|Static/dynamic||SRAM is static.||DRAM is dynamic.|
|Speed||SRAM is fast.||DRAM is slower than SRAM.|
|Power||SRAM consumes less power.||DRAM consumes more power than SRAM.|
|Transistors||SRAM uses more transistors per bit of memory.||DRAM uses fewer transistors per bit of memory.|
|Value||SRAM is expensive.||DRAM is cheaper.|
|Used in||SRAM is commonly used in cache memory.||DRAM is used in main memory.|
Q.2 vii) Give few characteristics of secondary storage devices
Secondary storage devices are used for storing data permanently in computer system. Their characteristics are as follows:
- It is a non-volatile memory i.e. it does not require continuous power to store data.
- The storage capacity of these devices is very high. It can store data up to TaraBytes.
- They are cheaper than main memory.
- They can be reused even after data is erased and stored anytime.
- They can be sequential, random or direct access.
Q.2 viii) Differentiate between the following.
a) Chip memory and Magnetic memory
b) Cache and Register ‘
c) Volatile and non-volatile memory
d)Magnetic tapes and Magnetic disks
e) EPROM and EEPROM
a) Chip memory and Magnetic memory.
The difference between Chip and magnetic memory is as follows:
|Headings||Chip memory||Magnetic memory|
|Parts||They don’t have moving parts.||They have moving parts called tracks.|
|Data storage||Data is stored electronically.||Data is stored magnetically.|
|Speed||Chip memory is faster.||Magnetic memory is comparatively is slower.|
|Reliability||Its data is more reliable.||Its data is not that much reliable after specific time.|
|Example||Flash memory etc.||Hard disk etc.|
b) Cache and registers:
The difference between cache and registers as follows:
|Visibility||Cache is completely transparent to software.||Registers are visible to software.|
|Managed by||Caches are completely managed by the hardware.||Registers are managed at compile time when the high level program is converted to machine specific assembly.|
|Located at||It is located next to CPU on separate chip.||These are located in the processor.|
|Number||There is one cache in computer memory.||There are number of registers in the processor.|
c) Volatile and non-volatile memory
The difference between volatile and non-volatile is as follows:
|What is it?||It requires an active power connection to function.||It does not require a continuous power to connection.|
|Retains information||Volatile memory retains the information as long as power is supplied.||Non-volatile memory retains information for ever.|
|Examples||RAM and Registers.||ROM, Flash memory, hard disk etc.|
d) Magnetic tapes and magnetic disks
The difference between magnetic tapes and magnetic disks are as follows:
|Headings||Magnetic tapes||Magnetic disks|
|Coating||Magnetic tapes are polymers coated with special material to store data.||Magnetic disks are metal disks that are coated with special material to store data.|
|External devices||A magnetic tape has storage parts that are touched by external devices.||A magnetic disk is not touched by external device.|
|Data access tape||The data access speed of magnetic tape is slower.||The data access speed of magnetic disk is fast.|
|Space.||Magnetic tape has comparatively less storage space.||Magnetic disk can hold more data per unit volume.|
|Examples||Audio cassettes, video cassettes etc.||Hard disk drives, floppy drives etc.|
e) EPROM and EEPROM
The difference EPROM and EEPROM is as follows:
|Erased||EPROM has to be erased with exposure to ultraviolet rays.||EEPROM is erased electronically.|
|Casing||It has a Quartz window in the package to expose the chip ultraviolet light.||EEPROM are completely encased in an opaque plastic case.|
|Speed||EPROM is slower.||EEPROM is much faster.|
|Used as||Previously used as BIOS chips.||Currently used as BIOS chips.|
Q.3 i) Briefly explain the processor internal memory and its types.
Internal processor memory:
Internal processor memory is the part of main memory of computer. It is directly accessed by the CPU. It works very fast. There are two types of internal processor memory, these are:
1. Cache memory
1. Cache memory:
ache memory is a portion of the high speed static RAM (SRAM) and is effective because most programs access the same data or instructions over and over. If repeatedly used information is placed in cache, CPU will access it faster and more efficiently.
There are different levels of Cache. These are:
- Level 1 (L1) Cache: It is referred to as primary cache, internal cache or system cache. It exists in the microprocessor and is very fast and most expensive cache. Processor first checks the L1 cache memory.
- Level 2 (L2) Cache: It is commonly referred to as secondary cache or external cache. It is located on the motherboard on earlier computers. In modern computers it is found on the processor chip.
- Level 3 (L3) Cache: In modern computer L3 is located on motherboard. Its size is large in comparison to L1 and L2 cache.
Register is a memory component which resides within a CPU. These are high speed temporary memory used to help the CPU get access to data and instructions quickly and effectively. These are semiconductor devices whose contents can be read and write at extremely high speeds but which are held their temporarily during the execution of programs.
Registers are the top memory hierarchy. These are the fastest way for the system to manipulate data. These are measured by the number of bits they can hold. For example, an 8-bit register means it can store 8 bits of data or a 32-bit register means it can store 32 bit of data.
The main registers are:
- Accumulator register (AC): It is used to store the result of arithmetic and logical instructions.
- Status register: It is also called Processor Status Word (PSW). It holds the system status indicators i.e. carry digits, overflow.
- Instruction register (IR): It is used to store the current instruction being executed.
- Program counter (PC): This register contains the address of the next instruction to process.
- Buffer register: This register is used temporarily store the data from memory.
Q.3 ii) Explain RAM and ROM along with their types in detail
Random Access Memory (RAM):
RAM is also called primary storage of computer. It is the working area of computer. It is Read and Write (R/W) memory. It is a volatile memory means that all data will be lost when power goes off. It holds data and instructions temporarily. CPU gets that information from RAM when it needs that for processing. It is the most common type of memory found in computers.
RAM stands for Random Access Memory.
It has two different types:
– Static Random Access Memory (SRAM)
– Dynamic Random Access Memory (DRAM)
1) Static Random Access Memory (SRAM):
SRAM is a type of memory that retains data bits in its memory as long as power is being supplied. SRAM provides faster access to data and is more expensive than DRAM. SRAM is used for computer’s cache memory. It is called SRAM because it does not have to be periodically refreshed to maintain its state.
2) Dynamic Random Access Memory (DRAM):
DRAM is a type of memory used in most computers. DRAM must have an electric current to maintain electrical state. It is called DRAM because it is periodically refreshed to maintain its state. DRAM is used as internal memory of computer as it has simple structure and it is also cost effective with high storage.
It has two types:
– DDR SDRAM
SDRAM stands for Synchronous Random Access Memory.
It is semiconductor memory with very high speed. It is improved version of earlier DRAM. It’s working is synchronized with system data bus, because of this it’s speed is very in operation than non-synchronous RAM.
2.2) DDR SDRAM
DDR SDRAM stands for Double Data Rate SDRAM. It is improved technology of SDRAM. It allows data transfer at double speed. Types of DDR SDRAM used today are:
- DDR1 RAM (Double Data Rate)
- DDR2 RAM
- DDR3 RAM
DDR2 and DDR3 are used in computers nowadays. DDR3 RAM is shown below in figure:
Read Only Memory (ROM):
ROM is a non-volatile memory i.e. it retains the information stored in it even when power is not supplied. So, it is permanent storage device. ROM is written by manufacturers not by users or programmers.
ROM has following types:
I. Programmable Read Only Memory (PROM)
II. Erasable Programmable Read Only Memory(EPROM)
III. Electrically Erasable Programmable Read Only Memory (EEPROM)
PROM is the type of ROM which is programmed only for once after it has been created and then it can never be changed. Once it has been programmed, the information written on it cannot be deleted or erased. Computer BIOS is an example of PROM.
EPROM is the type of ROM which is erasable for once. The data written on EPROM can be removed by using Ultra Violet Rays and it can be re-written. Its erasing time is about 20 minutes. Intel 8048 chip is an example of EPROM.
EEPROM is the type of ROM which can be erased and reprogrammed within milliseconds. It has a limited number of times for re-programming. Usually it can be re-programmed for 10,000 times. Flash drive is an example of EEPROM.
Q.3 iii) What is meant by secondary storage devices also explain the difference between Sequential access and Random access.
Secondary storage devices:
Secondary storage devices are one of the most valuable assets of the computer. It is storage where software and data can be stored on a permanent basis. Secondary storage is necessary because data is lost from memory or primary storage when a computer is turned off whereas secondary storage does not. Therefore, it is commonly known as non-volatile storage. The data on it stays forever until it is deleted or overwritten by the user.
Characteristics of secondary storage devices:
Some characteristics of secondary storage devices are as follows:
- It is non-volatile storage that is it retains data even after power is switched off.
- The storage capacity of these devices is very high.
- They are cheaper than main memory.
- They can be reused as data can be erased or deleted and then re-written.
- They can be either sequential, random or direct acces.
Examples of secondary storage devices:
Following are the some common examples of secondary storage devices:
- Floppy disks
- Hard disks
- Optical disks
- Magnetic tapes etc.
Difference between sequential and random access:
The differences between direct and sequential access are as follows:
|Headings||Sequential access||Random access|
|Storage||It can store data in volumes.||It can store data in disk blocks which uses more space.|
|Access||It access data in sequence.||It can access data randomly that is in any order.|
|Examples||Magnetic disks, magnetic tapes etc.||RAM, flash drives etc.|
Q.3 iv) Describe the following along with their advantages and disadvantages:
a) Magnetic tapes
b) Magnetic disks
c) Optical disks( CD, DVD, Blue Ray)
Magnetic tape is commonly used to record and store computer and video data.Magnetic tape is mainly used by large companies and organizations that require massive data storage.Following are the advantages nd disadvantages of magnetic tapes:
- A single magnetic tape cartridge can store large amount of data up to 1 Terabyte.Large cartidge are used by big companies and institutions that require continuous recording and backup of data.
- Data collection can go on without interruption overnight or for an entire weekend.
- Magnetic tape can be recorded over and reused repeatedly.
- Large amounts of information is stored.
- Magnetic tape is inexpensive and budget friendly.
- Special equipment must be purchased and set up for recording and storing data. The data can only be read on the special equipment.
- If the data is stored near a strong magnetic field or a large speaker,the tape can be damanged.
- Magnetic tape has a lifespan of 15 years.Data quality gradually erodes over time.
- It is necessary to keep older tape equipment just to be able to read the stored data.
A magnetic disk is a storage device that use a magnetization to write,rewrite and access data.It is a covered with a magnetic coating and stored data in the form of tracks,spot,and sectors.Hard disks and floppy disks,zip disks are common example of magnetic disks.
- Unlike the magnetic tapes, which support sequential access of data, magnetic disks support direct access of data. Hence, they are more suitable for wider range of applications.
- Due to its random access property,magnetic disks are often used as online secondary storage devices,in which case they store data of multiple users of the computer system.A tape is not suitable for such type of usage,due to its sequential-access property.
- Expect for the fixed type Winchester disks,the storage capacity of other magnetic disks is virtually unlimited, because as many disks as required can be used for storing very large data sets.
- Due to their low cost and high data recording densities that magnetic dis, the cost per bit of storage is low for magnetic disks. An additional cost benefit is that magnetic disks can be erased and refused many times.
- Floppy disks and zip disks are compact and light in weight.Hence, they are easy to handle and store.Very large amount of data can be stored in a small storage space.
- Data transfer rate for a magnetic disk system is normally higher than a tape system.
- Magnetic disks are less vulnerable to data corruption due to careless handling or unfavorable temperature and humidity conditions than magnetic tapes.
- Although magnetic disks may be used for both types of application, for applications of the latter type, use of magnetic disks may be less efficient than magnetic tapes.
- It is more difficult to maintain the security of information stored on magnetic disks, which are used as shared, online secondary storage devices as compared to information stored magnetic tapes or on other types of magnetic disks.
- For Winchester disks, a disk crash or drive failure often result in the loss of entire data stored on it.It is not eay ro recover the lost data. Hence,suitable backup procedures are suggested for data stored on Winchester disks.
- Some type of magntic disks, ssuch as disk pack and Winchester disks, are not so easily portable like magnetic tapes.
- On a cost-per-bit basis, the cost of magnetic disk is low, but the cost of magntic tapes is even low.
- They must be stored in a dust – free environment.
- Floppy disks, zip disks and disk packs should be labeled properly to pervent erasure of useful data by mistake.
An optical disks is an electronic data storage medium that can be written to and read using a low-powered laser beam.Few advantages and disadvantsges on optical disk:
- The cost – per-bit of storage for optical disks is very low, because of their low cost and enormous storage density.
- The use of a single spiral track makes optical disks an ideal storage medium for reading large blocks of saquential data, such as music.
- Optical disk drives do not have any mechanical read\write heads to rub against or crash into the disk surface.This makes optical disks a more reliable storage medium than magnetic tapes or magnetic disks.
- Optical disks have a data storage life in excess of 30 years.This makes them a better storage medium for data archiving as compared to magnetic tapes or magnetic disks.
- Since data once stored on an optical disk become permanent, the danger of stored data getting inadvertenly erased/overwritten is not there with optical disks.
- Due to their compact size and light weight, optical disks are easy to handle, store,and port from one place to another.
- Music CDs can be played on a computer having a CD-ROM drive along with a sound board and speakers.This allows computer systems to be also used as music system,whenever desired.
- It is a read-only(permanent) storage medium.Data once recorded, cannot be erased, and hence, the optical disks cannot be reused.
- The data access speed for optical disks is slower than magnetic disks.
- Optical disks require a more complicated drive mechanism than magnetic disks.
Q.3 v) Describe the following chip Memories with their advantages and disadvantages.
a) Flash Memory
b) Memory Cards
Flash Memory storage devices are typically small, lightweight, removable and rewritable.They consist of asmall printed circuit board which is encased in plastic or metal casing.They usually have a removable cap with covers and protects the part of the stick which is inserted into a usb port.Memory sticks are avaliable from 1 Gb upwards.Following are the advantages and this advantages of flash memory:
- They are more compact and portable than CDs or DVD.
- They hold more data than CD,many gigabytes.
- They are reliable as they have no moving parts(unlike a hard disk).
- They are easily branded on their cover to reflect the organization.
- They are not affected by magnetic fields(unlike magnetic tape).
- More expensive than CD or DVD as a medium.
- They can be easily lost.
- The metal part which is inserted into the USB port can be snapped off damaged if they handled roughly.
A memory card is a small storage device,which is used to store your data backups suck as text,picture,audio,and video.There are few advantages and disadvantages of memory card:
- Memory card have non-volatile memory,which keeps data stable on the card.Data on them are not theartened by loss of power source, and need not to be periodically refreshed.
- They are solid state media hence free from mechanical difficulties or damages.
- The new generation memory cards are smaller, lighter amd compact with higher storage capacity.
- They require less amount of power.
- They are highly portable.They can be easily used in number of small,lightweight and low-power devices.
- They do not produce any noise while on work
- They allow more immediate access.
- They come in all sort of sizes.The 64GB SD cards are most common one.
- They have relatively large storage space compared to old backup devices.
- They can easily fit in memory card slot in different devices and are easily removable.
- They can be used in different devices such as cameras, com[uters or mobile phones.
- They are easy to keep track of.
- One can use large card for cost effectiveness.
- Memory cards do not need organization.
- They can break easily.
- They can be lost, misplaced or smashed.
- These cards may be affected by electronic corruption and make entire card unreadable.