Cmp 101 Set 7 Memory

8/4/2019 Cmp 101 Set 7 Memory

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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.htm


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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

Documents

Cmp 101 Set 7 Memory