پنجشنبه ۲۲ شهریور ۰۳ | ۲۰:۰۰ ۸ بازديد
Sarita,Vikki,SRCC,DU E-RESOURCE 55
Memory: It is a storage device used to store information in
computers. The semiconductor memory is organized into
memory cells or bistable flip-flops, each storing one
binary bit (0 or 1). The memory cells are grouped into
words of fix word length, for example 1, 2, 4, 8, 16, 32, 64
or 128 bit. Each word can be accessed by a binary address
of N bit, making it possible to store 2 raised by N words in
the memory
Sarita,Vikki,SRCC,DU E-RESOURCE 56
for digital information?
A bit is a binary digit, the smallest increment of data on a
computer. A bit can hold only one of two values: 0 or 1,
corresponding to the electrical values of off or on,
respectively.
Because bits are so small, you rarely work with information
one bit at a time. Bits are usually assembled into a group of
eight to form a byte. A byte contains enough information to
store a single ASCII character, like “k” (maybe 00101101).
Sarita,Vikki,SRCC,DU E-RESOURCE 57
memory units are used:
Unit
1 bit 1 nibble 1
Byte
1 Kilobyte (KB)
1 Megabyte
(MB) 1 Gigabyte
(GB)
1 Terabyte (TB)
1 Petabyte (PB)
Sarita,Vikki,SRCC,DU
Equivalent
0 or 1
a group of 4 bits a
group of 8 bits 103
(i.e.,1024 bytes) 106
bytes 109 bytes 1012
bytes 1015 bytes
E-RESOURCE
in computers:-
Registers: Small memory, internal to processor, where actual
processing is done.
Cache Memory: Catches some of content of main memory
which current in use of the processor.
Main Memory (RAM/ROM): Large memory which is fast
but not as internal Processor memory.
All the above memories are volatile memories
because the stored information is lost when the power is
removed from the system.
Sarita,Vikki,SRCC,DU E-RESOURCE 59
It allows both read/write operations.
ROM: Read Only Memory. It is non-volatile memory.
It allows only read operations.
Random Access Memory (RAM) is a form of
computer data storage. Today, it takes the form of integrated
circuits that allow stored data to be accessed in any order.
Other memory devices (magnetic tapes, floppy discs, CDs and
DVDs) can access the storage data only in a predetermined
order, because of mechanical design limitations. The two
main forms of modern RAM are Static RAM (SRAM) and
Dynamic RAM (DRAM).
Sarita,Vikki,SRCC,DU E-RESOURCE 60
Sarita,Vikki,SRCC,DU E-RESOURCE 61
Secondary Memory; Very large memory. It is a nonvolatile
permanent memory.
• Eg; Magnetic disk (Hard / Floppy) memory, Magnetic Tape
memory etc.,
HDD (Hard Disk Drive): It is a mechanism which drives
Hard Disks to rotate and controls the flow of data between
hard disk and computer. Both hard disk and hard disk
drive comes in a single unit, it is permanently fixed in a
system unit.
Sarita,Vikki,SRCC,DU E-RESOURCE 62
retrieving digital information, primarily computer data. It
consists of one or more rigid (hence "hard") rapidly
rotating discs (platters usually rotating at 7,200 RPM)
coated with magnetic material, and with magnetic heads to
write data to the surfaces and read it from them.
Magnetic recording A hard disk drive records data
by magnetizing a thin film of ferromagnetic material on a
disk. Sequential changes in the direction of magnetization
represent binary data bits. The data is read from the disk
by detecting the transitions in magnetization
dfs3434