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Fundamentals of Computer and
programming in C
(CMP 101 )
MEMORY
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Memory
Main memory consists of a number of
storage locations, each of which isidentified by a unique address
The ability of the CPU to identifyeach location is known as itsaddressability
Each location stores a word i.e. thenumber of bits that can be processedby the CPU in a single operation.Word length may be typically 16, 24,32 or as many as 64 bits.
A large word length improves systemperformance, though may be lessefficient on occasions when the full wordlength is not used
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Main Memory
Storage Evaluation
Criteria
Explanation
Storage capacity Maximum number of bytes/words.
Access time Time required to locate and retrieved stored data.
Cost per bit of storage Cost of a memory unit of a desired capacity.
Volatile/Nonvolatile Volatile memory looses data when power source is
turned off or interrupted. Nonvolatile memory retains
data when power is turned off or interrupted.
Random access In random access memory (RAM) every data item can
be accessed independently at any instance of time.
Main memory, primary memory or simply memory is usedby CPU to store/retrieve data and instructions temporarily.
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Why more bits? Larger numbers
and address space
Mainmemory
Interfacing
device
requeststo read or
write
contents
Controller
Addresses Contents
0
1
2
3
4
5
-
-
-
- 1 2 n
Address buss: Sends thememory address of the data.Address space: Number of memorybyte or wordsAddress space = 2n where nis the
number of bits in address bus.
Data buss
Bits
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Fixed and variable length memory
Word addressable memory: Where each word is offixed size 16-bits, 32-bits or 64-bit words. They canstore 2, 4 or 8 characters (or bits). Such memory isviewed as fixed length memory.
Character (or byte) addressable memory is viewed asvariable length memory.
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Types of main memory
There are two types of main memory, Random Access Memory (RAM) and
Read Only Memory (ROM)
Random Access Memory (RAM)
holds its data as long as the computer is switched on
All data in RAM is lost when the computer is switched off
Described as being volatile
It is direct access as it can be both written to or read from in any order
Its purpose is to temporarily hold programs and data for processing. Inmodern computers it also holds the operating system
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Types of RAM
1. Dynamic Random Access Memory (DRAM)
Contents are constantly refreshed 1000 times per second
Access time 60 70 nanoseconds
Note: a nanosecond is one billionth of a second!
2. Synchronous Dynamic Random Access Memory (SDRAM)
Quicker than DRAM
Access time less than 60 nanoseconds
3. Direct Rambus Dynamic Random Access Memory (DRDRAM)
New type of RAM architecture
Access time 20 times faster than DRAM
More expensive
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4. Static Random Access Memory (SRAM)
Doesnt need refreshing
Retains contents as long as power applied to the chip
Access time around 10 nanoseconds
Used for cache memory
Also for date and time settings as powered by small battery
5. Cache memory
Small amount of memory typically 256 or 512 kilobytes
Temporary store for often used instructions
Level 1 cache is built within the CPU (internal)
Level 2 cache may be on chip or nearby (external)
Faster for CPU to access than main memory
Types of RAM
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The operation of cache memory
1. Cache fetches datafrom next to currentaddresses in mainmemory
2. CPU checks to seewhether the nextinstruction it requires is incache
3. If it is, then theinstruction is fetched from
the cache a very fastposition
4. If not, the CPU has to
fetch next instructionfrom main memory - amuch slower process
Main
Memory
(DRAM)
CPU
Cache
Memory
(SRAM)
= Bus connections
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Types of RAM
6. Video Random Access memory
Holds data to be displayed on computer screen Has two data paths allowing READ and WRITE to occur at the same time
A systems amount of VRAM relates to the number of colours and resolution
A graphics card may have its own VRAM chip on board
7. Virtual memory
Uses backing storage e.g. hard disk as a temporary location for programsand data where insufficient RAM available
Swaps programs and data between the hard-disk and RAM as the CPU
requires them for processing
A cheap method of running large or many programs on a computer system
Cost is speed: the CPU can access RAM in nanoseconds but hard-disk inmilliseconds (Note: a millisecond is a thousandth of a second)
Virtual memory is much slower than RAM
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Read only memory (ROM)
ROM holds programs and data permanently even when computer is switched off
Data can be read by the CPU in any order so ROM is also direct access
The contents of ROM are fixed at the time of manufacture
Stores a program called the bootstrap loader that helps start up the computer
Access time of between 10 and 50 nanoseconds
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Types of ROM
1. Programmable Read Only Memory (PROM)
Empty of data when manufactured
May be permanently programmed by the user
2. Erasable Programmable Read Only Memory (EPROM)
Can be programmed, erased and reprogrammed
The EPROM chip has a small window on top allowing it to be erased byshining ultra-violet light on it
After reprogramming the window is covered to prevent new contents beingerased
Access time is around 45 90 nanoseconds
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Types of ROM
3. Electrically Erasable Programmable Read Only Memory (EEPROM)
Reprogrammed electrically without using ultraviolet light
Must be removed from the computer and placed in a special machine to do this
Access times between 45 and 200 nanoseconds
4. Flash ROM
Similar to EEPROM
However, can be reprogrammed while still in the computer
Easier to upgrade programs stored in Flash ROM
Used to store programs in devices e.g. modems
Access time is around 45 90 nanoseconds
5. ROM cartridges
Commonly used in games machines
Prevents software from being easily copied
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Memory configurations for Intel CPUs
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Read about the following Computer
Memory Types
L1 cache
L2 cache
RAM - the Main Memory
DRAM
Fast Page Mode DRAM
EDO DRAM
SDRAM
PC133
SDRAMDDR
SDRAM
DDR2 SDRAM
Dual-channel DDR
1T-SRAM
Direct RDRAM
SIMMs
DIMMs
RIMMs
Presence detect
Parity memory
ECC memoryMemory upgrades
Evolution
Flash memory
Magnetic RAM
http://www.pctechguide.com/14Memory_L1_cache.htmhttp://www.pctechguide.com/14Memory_L2_cache.htmhttp://www.pctechguide.com/14Memory_Main_memory.htmhttp://www.pctechguide.com/14Memory_DRAM.htmhttp://www.pctechguide.com/14Memory_FPM_DRAM.htmhttp://www.pctechguide.com/14Memory_EDO_DRAM.htmhttp://www.pctechguide.com/14Memory_SDRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_DDR_DRAM.htmhttp://www.pctechguide.com/14Memory_DDR_DRAM.htmhttp://www.pctechguide.com/14Memory_DDR2_DRAM.htmhttp://www.pctechguide.com/14Memory_Dual-channel_DDR.htmhttp://www.pctechguide.com/14Memory_1T-SRAM.htmhttp://www.pctechguide.com/14Memory_Direct_RDRAM.htmhttp://www.pctechguide.com/14Memory_SIMMs.htmhttp://www.pctechguide.com/14Memory_DIMMs.htmhttp://www.pctechguide.com/14Memory_RIMMs.htmhttp://www.pctechguide.com/14Memory_Presence_detect.htmhttp://www.pctechguide.com/14Memory_Parity_memory.htmhttp://www.pctechguide.com/14Memory_ECC_memory.htmhttp://www.pctechguide.com/14Memory_Memory_upgrades.htmhttp://www.pctechguide.com/14Memory_Evolution.htmhttp://www.pctechguide.com/14Memory_Flash_memory.htmhttp://www.pctechguide.com/14Memory_Magnetic_RAM.htmhttp://www.pctechguide.com/14Memory_Magnetic_RAM.htmhttp://www.pctechguide.com/14Memory_Flash_memory.htmhttp://www.pctechguide.com/14Memory_Evolution.htmhttp://www.pctechguide.com/14Memory_Memory_upgrades.htmhttp://www.pctechguide.com/14Memory_ECC_memory.htmhttp://www.pctechguide.com/14Memory_Parity_memory.htmhttp://www.pctechguide.com/14Memory_Presence_detect.htmhttp://www.pctechguide.com/14Memory_RIMMs.htmhttp://www.pctechguide.com/14Memory_DIMMs.htmhttp://www.pctechguide.com/14Memory_SIMMs.htmhttp://www.pctechguide.com/14Memory_Direct_RDRAM.htmhttp://www.pctechguide.com/14Memory_1T-SRAM.htmhttp://www.pctechguide.com/14Memory_1T-SRAM.htmhttp://www.pctechguide.com/14Memory_1T-SRAM.htmhttp://www.pctechguide.com/14Memory_Dual-channel_DDR.htmhttp://www.pctechguide.com/14Memory_Dual-channel_DDR.htmhttp://www.pctechguide.com/14Memory_Dual-channel_DDR.htmhttp://www.pctechguide.com/14Memory_DDR2_DRAM.htmhttp://www.pctechguide.com/14Memory_DDR_DRAM.htmhttp://www.pctechguide.com/14Memory_DDR_DRAM.htmhttp://www.pctechguide.com/14Memory_DDR_DRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_PC133_SDRAM.htmhttp://www.pctechguide.com/14Memory_SDRAM.htmhttp://www.pctechguide.com/14Memory_EDO_DRAM.htmhttp://www.pctechguide.com/14Memory_FPM_DRAM.htmhttp://www.pctechguide.com/14Memory_DRAM.htmhttp://www.pctechguide.com/14Memory_Main_memory.htmhttp://www.pctechguide.com/14Memory_Main_memory.htmhttp://www.pctechguide.com/14Memory_Main_memory.htmhttp://www.pctechguide.com/14Memory_Main_memory.htmhttp://www.pctechguide.com/14Memory_L2_cache.htmhttp://www.pctechguide.com/14Memory_L1_cache.htm8/4/2019 Cmp 101 Set 7 Memory
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The basic rule--which states that the number
of transistors on a chip doubles every 24
months--has been the guiding principle of the
high-tech industry since it was coined by Intel
co-founder Gordon Moore in 1965.
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Limitations of Primary Storage
Limited Capacity: It cannot be used to store the large
volumes of data items.
Volatility: Looses data when electric power is turned
off or interrupted. Data Portability: It cannot be used to port the data
from one place to other.
These limitations lead to the development of
auxiliary memory or secondary storage devices.
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Secondary Storage Devices
Sequential
Access Devices
Direct Access
Devices
Magnetic Tape Magnetic Disk Optical Disk
Hard
Disk
Floppy
Disk
CD-ROM WORM
Disk
ZIP
Disk
Disk
Pack
Winchester
Disk
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Magnetic Tape
The first truly mass
auxiliary storage device
was the magnetic tape
drive
Tape drives have amajor problem; canyou describe it?
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0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L N O P
1
1
1
0
0
0
1
7
6
5
4
3
2
1
Numeric
zone
Parity bit
Track/Channel
numbers
7 Track;6-bit BCD; Even parity (all tracks must have even number of 1)
A frame
6-bit BCD for letter A (Table 4.2 page 36
Even parity (all tracks must have even number of 1)
Error Checking
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0 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L N O P
0
0
1
1
0
0
0
1
0
9
8
7
6
5
4
3
2
1
Track/Channel
numbers
9 Track;8-bit EBCDIC; Even parity (all tracks must have even number of 1)
A frame
8-bit EBCDIC for letter A (Table 4.3 page 8
Odd parity (all tracks must have odd number of 1)Error Checking
3s digit
2s digit
Added Zone
Added Zone
Zone
Parity bit
Zone
Units digit
4s digit
1 1 0 0 0 0 0 1
EBCDIC for the letter A
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Terminologies
Inter record gap (IRG)
Blocking factor: # of records perblocks
Inter Block gap (IBG)
Blocks: Records are grouped into blocks
Record: Group of characters separated by blank
Storage capacity of tape= Data recording density x LengthData transfer rate (bytes/second to main memory
Tape drive
Tape controller
Tape Types (Half-inch tape reel, Half-inch tape
cartridge, Quarter-inch streamer tape and 4mm
Digital Audio Tape (DAT)
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Advantages & Limitations of Magnetic
Tape
Advantages
Virtually unlimited
storage capacity.
Low cost. Easy to handle and store.
Easy to port.
Limitations
The are not suitably for
frequent data access.
Must be operated industless environment.
Must be operated in
controlled environment.
Must have properidentification labels
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Uses of Magnetic Tape
Good for applications that require sequential
data processing.
Data backup.
Data archiving.
Physically large data transfer
Software distribution
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Magnetic DisksA platter coated with iron oxide: A
magnetizable material
Generally 8 bit EBCDIC code
is used to record the data
items.Surface: 2 surfaces per disk.
Tracks:000-199.
Sectors: 8 sectors per track.
Disk pack: 200 disks.
Cylinder: Each track from
all recording surfaces in adisk pack form a cylinder.
Storage capacity = # of
surfaces # of tracks per
surfacex # of sectors per
track x# of bytes per sector.
Access mechanism:Read/write head moves to
an address by specifying the
(disk #, track #, sector #,
byte #)
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Magnetic Disks
Seek Time: Time to move the R/W head to the desired track.Latency or Rotational Delay Time: Time to rotate the disk to thedesired sector of a track.
Average Latency Time?Transfer Rate:Rate at which data to be written/read. Transfer rate =n x r /60 where n is the # of bytes per track and r is the revolution per
second.
Disk Formatting: Formatting prepares a disk to be used by differentdisk drives. Formatting creates file allocation table (FAT) that specifies
the track and sector of the data items.
Important: Magnetic Disks are direct or random access devicebecause data items can be accessed by specifying its address.
Disk drives with interchangeable disks.Disk drives with fixed disks.Disk Controller: Controls the movement of R/W heads, and disk
rotation.
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Magnetic
Disk
FloppyDisk (1.4 MB)
HardDisk
Zip Bernoulli
Disk
(Portable/Fixed)
Disk
Packs
Winchester
Disk
Magnetic Disk Type
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Advantages & Limitations
Advantages
Direct Access.
Simultaneous sharing.
On-line/Off-line access. Unlimited disk may be
added.
Low cost.
Portable Fast
Limitations
Inefficient for sequential
data processing.
Sharing make dataunsecured
Disk failure.
Cost of magnetic tape is
lower Must be operated in
dustless environment
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Uses of Magnetic Drives
Random access applications
Shared on-line secondary storage.
Data backup. Data archiving
Data and software transportation.
Software distribution.
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OPTICAL DISK
In the optic readable CD-ROM, the data
storage consists of millions of indentations
burnt into light reflecting silver surface. The
burnt dents reflect less light than the shinysurface.
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Tracks
The CD-ROM has onlyone track, a spiralwinding its way from
the center to the outeredge. The spiral trackis ideal for readinglarge block of serial
data.
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Access MEchanism
A weak laser beam is sent to the disk through
a two-way mirror and the sensor registers the
difference in light reflection from the burnt
and shiny areas as zeros and ones.
Access time: 100-300 millisecond.
CD-ROM (Compact disk read only memory).
WORM (Write once read memory)
R/W CD (Read/Write compact disk)
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Advantages & Limitations
Advantages
Low cost
Ideal for reading large
volumes of data. No mechanical R/W
heads.
Long life data storage.
Easy to handle, store andport.
Limitations
Slower than magnetic
disk.
Complicated drive thanmagnetic disk.
Uses of optical disk
Distribution of large
amount of data andMulltimedia.
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Mass Storage
Disk Array: It uses a set of magnetic disks.
Automated tape library: Uses a set of
magnetic tapes.
CD-ROM jukebox: Uses a set of CDROM
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Cache
Memory
Main Memory
Hard DiskMagnetic tape, Floppy,
Mass Storage
Memory Hierarchy