Memory organisation is combination of several memory space devices efficiently. Memory devices are blended and organised predicated on their characteristic such as gain access to time, speed, safe-keeping capacity, physical size and cost per byte. Storage devices organised so that computer system should operate at highest velocity, provide bulky storage space capacity, smaller in proportions and less in a cost. Memory organisation uses primary recollection devices and supplementary ram devices.
3. 2 Ram Unit
Memory unit is storage unit of the computer system. It stores content such as instructions (rules) and data for temporary or permanent purpose. It is utilized to stores content also to retrieves this content when needed by CPU or customer. Memory unit includes two types of storage area: principal (main) and supplementary. Teaching or data given by suggestions devices is first getting stored in the principal recollection. Further users saves processed (carried out) data in the extra memory. Primary ram is volatile (temporary). It really is faster than supplementary memory. It offers RAM and ROM. It really is immediately accessible by CPU. Extra storage is non-volatile (long lasting). It offers several secondary storage area devices such as Hard Disk Drive (HDD), Floppy Disk Drive (FDD), CDROM, and DVD etc. Figure 3. 1 shows ram product and communication series with other items.
Note: Volatile storage loses its content when computer loses electricity. In non-volatile memory power loss of computer does not influences content.
Input Unit
Process Unit
Output Unit
Primary Memory
Secondary Memory
Memory Unit
3. 3 Storage area hierarchy
Memory organisation includes various recollection devices. These devises are structured in a hierarchy based on the characteristics of memory devices. Memory space hierarchy explains the series of accessing storage device while digesting, in the computer system. Recollection is organized in the hierarchy so that computer system should give excellent performance. Physique 3. 2 shows Memory space hierarchy. Hierarchy is manufactured on the basis of characteristics of memory, they are outlined as follow:
Access Time - Time considered by memory to read or write data. It really is assessed in milliseconds (ms) or in nanoseconds (ns).
Memory size - It is amount of memory. Measured in KB, MB, GB or TB.
Cost per byte - It really is cost required to gain access to per byte.
Transfer bandwidth - It really is rate of the recollection. It assessed in MHz, GHz.
Unit of transfer - Data transfer rate. Measured in Kbps, Mbps or Gbps.
Increasing velocity and cost per bit dcreeasing sisize
Registers in CPU
Level one cache
Level two cache
Main memory
Virtual Memory
Increasing Size, lessening velocity and cost
capacity
Secondary Storage area devices
Figure 3. 2 Storage Hierarchy
Memory hierarchy includes CPU registers on the top. Register provides quickest data access and it is one of the most expensive memory space location.
Second and third levels are level-1 and level-2 cache respectively. The particular level one cache is small in proportions (4 KB to 32 KB) though much larger than register. It is fixed on CPU chip so end user can not expand.
The level-2 cache is present on some CPUs only. It is much bigger than level-1 cache. User can not grow it as it is fixed on CPU chip but it is cheaper than level-1 cache.
Virtual memory space is part of drive drive, which simulates to Random Gain access to Memory (RAM). Drive drives are less costly; so cost per little is significantly less. Secondary safe-keeping devices are such as Hard Disk Drive (HDD), Floppy Disk Drive (FDD), COMPACT DISC Read Only Storage area (CDROM), Digital Versatile Disk (Dvd and blu-ray) and tape drives. It really is bit slower.
3. 4 Recollection types
Basic reason for memory space is to store content. Still ram is available in various types. Basic type of memory is primary memory and secondary memory. Types are created based on memory characteristics and its own role in the computer system. Main memory space is the first memory utilized by CPU, so it should be faster and easily accessible. To make key memory as per the requirement, ram organisation includes Ram memory and ROM as most important memory. The primary use of extra memory space is use to store user's data completely. Speed of secondary recollection can be affected, but storage capacity should be excellent. So memory company includes HDD, FDD, and CDROM and so on as a second memory. Figure 3. 2 shows types of storage.
3. 4. 1 Key Memory
Primary recollection is access directly by CPU. Principal divided into two types RAM and ROM. Major storage area should be faster and easily accessible.
RAM - Ram memory is, the burkha memory used in the computer. Memory is the key storage area of the computer system. It is volatile since its content is obtainable only so long as the computer is ON. The content of Memory is cleared when computer is powered OFF. It really is at third devote the storage area hierarchy. Operating system, request program and jogging data are filled in the RAM. CPU straight accesses the RAM.
Types of RAM are the following:
Static Random Gain access to Storage area (SRAM) - SRAM is made with several transistors, usually 4-6, for each memory space cell. It does not require refresh time as capacitors aren't used. It is much faster and costlier than DRAM. Computer system use SRAM as cache recollection.
DRAM (Dynamic Random Access Memory) - It offers memory cells with a combined transistor; it uses capacitor, as capacitors gradually leaks with as they stared discharging, so need periodic refresh. It is slower and chippers than SRAM. It really is much denser (stores many parts per chip). It requires less vitality and creates less heat when compared with the SRAM. DRAM is available in several forms such as SDRAM, then DDRAM to RDRAM.
Read Only Recollection (ROM) - ROM is non-volatile main recollection. Data written on ROM can not erase or overwrite. Data is used up on the ROM as firmware. ROM recollection can be used in the computer system to create firmware for example BIOS program.
Types of ROM are the following:
Programmable read-only storage area (PROM) - This type of memory is one time written ram. Once program is written can not be change.
Erasable programmable read-only memory space (EPROM) - Data written on EPROM can be erased. Ultraviolet is used to erase the info written on PROM.
Electrically erasable programmable read-only memory space (EEPROM) - It is identical to EPROM but to remove data entirely it needs electrical signal. So not require to remove from computer. Data can be erased or higher written it the computer itself.
3. 4. 2 Supplementary Memory
A secondary storage is non-volatile. Secondary memory used to save lots of user's data permanently. Devices used as extra memory space are HDD, FDD, Compact disk, Dvd movie, Tape drives and so forth. Secondary memory reaches sixth put in place the memory hierarchy.
Devices used as extra memory are outlined as follows:
Floppy Drive Drives (FDD) - Used as magnetic, lightweight storage area device. It stores maximum 1. 44 MB data. Earlier it used to transfer data among personal computers.
Hard Disk Drives (HDD) - HDD is fixed, magnetic memory device. It is vital in the computer system because OPERATING-SYSTEM and user's data is saved on the HDD. Storage area capacity of HDD is vendor specific.
CDROM and DVDROM - Are optical recollection units used for transferring data and programs on the list of computers. CDs are available in the scale 650MB, DVDs can be found up to 4 GB in a size.
Tape drives - Are usually used for data backup purpose.
3. 6 Cache Memory
The cache is little bit of memory with broadband. Cache memory helps to keep data and code (introductions) that are used by CPU often. Use of cache recollection reduced the longing time of CPU that makes CPU more effective. SRAM is used to make cache ram. SRAM will not required refresh as it generally does not use capacitors as DRAM, it is 10 times faster than DRAM. Cache is of two types Level-1 that is placed ion the CPU. Level 2 cache is optional some processors have this kind of storage that is some time put inside the CPU or positioned not far from CPU. To do next training, CPU first check cache ram for the same teaching if that training is unavailable then it runs further.
Note: DRAM is made up of capacitors which need frequent refreshing to protect data. SRAM uses flip-flop circuit that does not require refresh.
3. 6. 1 Cache lines replacement Algorithms
While a new line is packed in the cache, one of the prevailing lines must be replaced. Direct mapped cache, same stop from brand is removed happen for new one. In associative cache, it can seek out another place.
Four of the most frequent line replacement unit algorithms are the following:
LRU (Lease Just lately Used) - the cache range that was previous referenced in the most distance recent is changed.
FIFO (First In - First Out) - the cache brand from the place that was filled in the most distant past is substituted.
LFU ( A minimum of COMMONLY USED) - the cache series that has been referenced the changing times is substituted.
Random - a arbitrarily selected range from cache is replaced.
Note: The mostly used algorithm is LRU.
Cache Terminology
Cache use few terminology for procedure are the following:
Hit - A cache access discovers data the cache memory
Miss - A cache gain access to will not find data or instruction, forcing usage of next memory space down in recollection hierarchy.
Miss percentage - Percent of misses to data in comparison to all accesses.
Hit gain access to time - Quantity of clocks to come back a cache hit
Miss penalty - Amount of clocks to process a cache miss.
Virtual Memory
Operating system allows a process by which space of hard drive can be simulate to Ram memory. The HDD space used as Memory is known a Virtual Ram.
As cost per byte of HDD is less, so online memory is effective to perform many large programs that require more memory. Access time of Memory is within nanoseconds but electronic memory gives gain access to time in milliseconds. It really is much slower than RAM. Number 5. 1 shows operation of virtual storage area.
Virtual storage area uses paging and segmentation terminologies. Conditions used by paging are as follows:
Virtual address- Address utilized by application program from electronic memory. It really is composed of webpage number and site offset.
Physical address - Address of physical storage.
Page - online space divided into fixed-size pages.
Frame - Physical storage area divided into predetermined frames size.
MMU - Storage area Management Unit (MMU) used to map virtual address to home address.
Page desk - Each process has its page table. Each page table entry provides the frame quantity of the corresponding site in main memory
Figure 3. 4 Virtual memory operations
3. 8 Chapter Review Questions
Which of the following is principal volatile storage area?
(A)
RAM
(C)
ROM
(B)
HDD
(D)
FDD
Ans: A
Which among the following are magnetic safe-keeping devices?
(A)
HDD
(C)
FDD
(B)
CDROM
(D)
DVDROM
Ans: A and C
Maximum safe-keeping capacity FDD is -------
(A)
2GB
(C)
2. 44 MB
(B)
1. 44MB
(D)
None of these
Ans: B
A ____ is utilized as cache memory space in the computer system.
(A)
SRAM
(C)
DRAM
(B)
SDRAM
(D)
ROM
Ans: A
Which of the following is main non-volatile recollection?
(A)
Cache
(C)
ROM
(B)
Virtual
(D)
None of these
Ans: C
Which of the next ROMs' content can be removed using ultraviolet?
(A)
PROM
(C)
EPROM
(B)
ROM
(D)
EEPROM
Ans: C
Virtual memory space is concept of --------------------
(A)
Using HDD space as RAM
(C)
Using FDD space as a RAM
(B)
Logical based
(D)
Protocol based
Ans: A
8. Within the memory hierarchy which storage area is at first level?
(A)
Register
(C)
L1 cache
(B)
L2 cache
(D)
None of these
Ans: A
9. Which storage takes second place in the memory hierarchy?
(A)
L1 cache
(C)
L2 cache
(B)
ROM
(D)
HDD
Ans: B
10. MMU means --------------------
(A)
Memory Combination unit
(C)
Memory Management Unit
(B)
Memory measurement Unit
(D)
None of these
Ans: C
3. 8. 1 Answers
1. A
2. A and C
3. B
4. A
5. C
6. C
7. A
8. A
9. B
10. C
Summary
In the chapter, Memory Company, you learned about:
Different memory items and its types.
Memory hierarchy based on storage characteristics.
Cache and its replacement unit algorithm.
Virtual memory space and paging.
