Lecture-4
MEMORY:
It is a storage device. It stores program instructions, data and
the results. There are two kind of memories; semiconductor
memories & magnetic memories. Semiconductor memories are
faster, smaller, and lighter and consume less power. Semiconductor
memories are used as the main memory of a computer. Magnetic
memories are slow but they are cheaper than semiconductor
memories. Magnetic memories are used as the secondary memories
of a computer for bulk storage of data and information’s. With the
development in technology, semiconductor memories are used
everywhere.
If a memory stores N- words of information each word being of
m bits, we say it is a N x m memory. E.g. 8x4 memory means there
are 8 words and each word containing 4- bit of information (called
nibble). 8 words are stored at 8-memory locations and these memory
locations are clearly identified by 8 unique addresses.
Table: Formulation of Memory Address
A2 A1 A0 Decimal Memory Contents of the
Equivalent Location memory location
0 0 0 0 0 M(0)
0 0 1 1 1 M(1)
0 1 0 2 2 M(2)
0 1 1 3 2 M(3)
1 0 0 4 3 M(4)
1 0 1 5 5 M(5)
1 1 0 6 6 M(6)
1 1 1 7 7 M(7)
, Addresses are formulated by bit combination available in wires known
as address lines. To identify 8-memory locations, 3 address lines
designated A2A1A0 are required. The memory locations identification
and the corresponding contents stored are shown in table. M(0) is the
content of memory location ‘0’ and it has 4 bits here. M(1) is the
content of memory location ‘1’ and so on. It can also be represented
as shown in fig.2.1.
A2 3
A1 or Address Bus
A0 A2-A0
Fig.2.1 Representation of Address Bus
The three address lines A2 A1 A0 together is known as address
bus. It is a unidirectional bus. The microprocessor always sends the
addresses.
In general, an Nxm memory shall have ‘k’ address lines
designated Ak-1 Ak-2 Ak-3 ……… A2A1A0 such that ‘k’ is the smallest
integer satisfying the inequality 2k ≥ N. e.g. 200x8 memory shall have
200 memory locations. Each location contains 8 bit of information. To
identify 200 memory locations we require a minimum of 8 (=k) lines
designated A7 A6 A5 A4 A3 A2 A1 A0. However k = 8 address lines can
identify a total of 256 memory location starting from (0000 0000)2 to
(1111 1111)2 or 00H to FFH. But we are using only 200 memory
locations and rests of the locations are redundant. The 200 memory
locations shall be identified starting from (00000000)2 to (11000111)2.
The other combinations (11001000)2 to (11111111)2 are not used in
this memory & are redundant addresses. Since it is too tiring & boring
MEMORY:
It is a storage device. It stores program instructions, data and
the results. There are two kind of memories; semiconductor
memories & magnetic memories. Semiconductor memories are
faster, smaller, and lighter and consume less power. Semiconductor
memories are used as the main memory of a computer. Magnetic
memories are slow but they are cheaper than semiconductor
memories. Magnetic memories are used as the secondary memories
of a computer for bulk storage of data and information’s. With the
development in technology, semiconductor memories are used
everywhere.
If a memory stores N- words of information each word being of
m bits, we say it is a N x m memory. E.g. 8x4 memory means there
are 8 words and each word containing 4- bit of information (called
nibble). 8 words are stored at 8-memory locations and these memory
locations are clearly identified by 8 unique addresses.
Table: Formulation of Memory Address
A2 A1 A0 Decimal Memory Contents of the
Equivalent Location memory location
0 0 0 0 0 M(0)
0 0 1 1 1 M(1)
0 1 0 2 2 M(2)
0 1 1 3 2 M(3)
1 0 0 4 3 M(4)
1 0 1 5 5 M(5)
1 1 0 6 6 M(6)
1 1 1 7 7 M(7)
, Addresses are formulated by bit combination available in wires known
as address lines. To identify 8-memory locations, 3 address lines
designated A2A1A0 are required. The memory locations identification
and the corresponding contents stored are shown in table. M(0) is the
content of memory location ‘0’ and it has 4 bits here. M(1) is the
content of memory location ‘1’ and so on. It can also be represented
as shown in fig.2.1.
A2 3
A1 or Address Bus
A0 A2-A0
Fig.2.1 Representation of Address Bus
The three address lines A2 A1 A0 together is known as address
bus. It is a unidirectional bus. The microprocessor always sends the
addresses.
In general, an Nxm memory shall have ‘k’ address lines
designated Ak-1 Ak-2 Ak-3 ……… A2A1A0 such that ‘k’ is the smallest
integer satisfying the inequality 2k ≥ N. e.g. 200x8 memory shall have
200 memory locations. Each location contains 8 bit of information. To
identify 200 memory locations we require a minimum of 8 (=k) lines
designated A7 A6 A5 A4 A3 A2 A1 A0. However k = 8 address lines can
identify a total of 256 memory location starting from (0000 0000)2 to
(1111 1111)2 or 00H to FFH. But we are using only 200 memory
locations and rests of the locations are redundant. The 200 memory
locations shall be identified starting from (00000000)2 to (11000111)2.
The other combinations (11001000)2 to (11111111)2 are not used in
this memory & are redundant addresses. Since it is too tiring & boring
