Read-only memory (ROM)
What is
read-only memory in computer organization and architecture?
Read-only memory (ROM)
·
is one of type of a
non-volatile computer memory types which means that storage that remain its data when power is
removed.
·
is
a class of memory-storage
devices used in computers and other electronic devices.
·
is one sort of memory that is implemented with
combinational circuits
o Combinational circuits often referred as “memoryless”
circuits because the output of
combinatinal circuits depends only on their curret input and
no history of prior inputs is retained.
·
is a memory unit that performs only the read
operation.
o So the binary information stored in a ROM is permanent and
was created during the fabrication process.
o Thus, a given input to the ROM (address lines) always
produces the same output (data lines).
o Due to the outputs are a function only of the present inputs,
the ROM is the fact a combinational circuit.
Notes
Storage can be internal or external (auxiliary)
Internal storage
·
Main
memory or random access memory (RAM)
·
Other
memory is read-only memory (ROM)
·
Both hardware and software: firmware
External (auxiliary)storage
·
Hard disks, floppy disks, magnetic tape
·
Flash drives
Data
stored in ROM cannot be modified
Used
·
for storing programs
·
for storing
data
A good example of ROM is EEPROM(erasable
programmable read only memory),
which is used for the computer BIOS.
Did ROM implemented with others?
A ROM can be implemented with a
decoder and a set of OR gates.As an example,consider table A.8 below
This
can be viewed as a truth tables with 4
inputs and 4 outputs. For each of the 16 possible input values, the
corresponding set of values of the outputs is shown. It can be viewed as
defining the contents of a 64-bit ROM
consisting of 16 words of 4 bits each. The 4 inputs specify an address, and the
4 outputs specify the contents of the
location specified by the address.
Adder
What
is adder in
computer organization and architecture?
Adder
·
or known as summer is a digital circuit that performs addition of numbers
Used
adders
are used in the
·
arithmetic logic unit(s),
·
other parts of the
processor that are used to calculate addresses, table indices, and similar
operations.
What
is half adder in computer organization
and architecture?
Half adder is a combinational circuit which performs addition of
two bits
A half-adder adds two 1-bit inputs and produces a
sum bit and a carry bit as outputs.
Half adder
Half Adder Logic Diagram
The
half adder adds two single binary digits A and B. Sum(S) and carry(C) is the
two outputs. The carry(C) signal represents an overflow into the next digit of
a multi-digit addition. The value of the sum is 2c+s. The simplest half-adder design, pictured on the top, incorporates
an XOR gate for S and an AND gate for C.
With the addition of an OR gate to combine their carry outputs, two half adders
can be combined to make a full adder.
We
can use two half adder to create a full adder by the following way
Full
Adder
What is full adder in
computer organization and architecture?
A full adder
·
is
a logical circuit that performs an addition operation on three one-bit binary
numbers(A, B and Carry(in)).
·
is
also called a (3,2) adder because it has 3 inputs and 2 outputs.
·
produces
a sum and a carry(out).
·
A and B are the operands, and Cin is a bit carried in from the next less
significant stage.
·
The full-adder is
usually a component in a cascade of adders, which add 8, 16, 32, etc. binary
numbers.
·
The circuit produces a two-bit output sum typically
represented by the signals Cout and S,
where
. The one-bit full adder's truth table is:
References
Written by,
Lai Wai Kuen
B031210027
No comments:
Post a Comment