Input / Output The input/output component of the Von Neumann architecture handles devices that allow a
computer system to communicate with other devices such as a screen(or monitor), keyboard,
printer, etc. It also allows a computer system to store information via storage devices such as
internal and external hard-drives, CD-ROMs, Memory stick(flash disks), etc.
There are two types of access methods where storage devices (mass-storage devices) can be
accessed by a computer system:
a. Direct Access Methods are applicable for hard-drives, CD-ROMs, memory stick
or flash disks and the like. Direct access means random access is possible.
b. Sequential Access Methods are applicable for tape drives where data can only
be accessed serially or sequentially. Sequential access means random access is not
possible
Characteristics of Input /Output (I/O) devices:
a. Compared to Memory or RAM, speed of I/O devices is slow, it is in the range of
milliseconds
b. In order to mitigate the slowness problem, I/O devices make use of controllers.
• A controller, which has a special purpose processor has a small memory
buffer, and a control logic to control I/O device (e.g. to move a disk
arm).
• This solution enables data transfer between RAM and the memory buffer,
and accessing data from the memory buffer is faster.
The ALU The Arithmetic/ Logic Unit(ALU) performs mathematical operations((+, -, x, /, …) and logic
operations (=, <, >, and, or, not, ...). The ALU is a sub-component of the CPU(Central
Processing Unit). The ALU is composed of:
• Circuits responsible for performing arithmetic/logic operations,
• Registers responsible for storing intermediate computational results,
and
• Bus that connects the two.
