Computer Architecture Input/Output-part 1

Function Of Input/Output Modules :

1. Control and Timing.
2. Processor Communication
3. Device Communication
4. Data Buffering.
5. Error Detection



Input/Output Module Structure

Data transferred to and from the module are buffered in one or more DATA REGISTERS.
STATUS REGISTER provide status information. They may also act as Control Register, to accept detailed control information from the processor.
The logic within the module interacts with the processor via a set of control lines. The processor uses the control lines to issue the commands to the I/O Modules. Some of the control lines may be used by the I/O Module (eg. for arbitration and status signals). The module must also be able to recognize and generate addresses associated with the devices it controls. Each I/O Module has a unique address or, if it controls more then one external device, a unique set of addresses.

An Input/Output Module that takes on most of the detailed processing burden, presenting a high-level interface to the processor, is usually referred to as an I/O CHANNEL or I/O PROCESSOR.

An I/O Module that is quite primitive and requires detailed control is usually referred to as an I/O CONTROLLER or DEVICE CONTROLLER.

Elements of Cache Design

Main elements of Cache design are

1. Cache Size : The size of the cache should be small enough so that the overall cost per bit is close to that of main memory alone and large enough so that overall access time is close to that of cache alone. Large caches tend to be slightly slower than smaller ones because of the fact that The larger the cache the larger the number of gates involved in addressing the cache.
2. Mapping Function : Direct, Associative or Set Associative.
3. Replacement Algorithm : LRU (Least recently Used), FIFO, LFU (Least Frequently Used) or some Random one.
4. Write Policy : Write Through, Write Back or Write Once.
5. Line Size
6. Number of Caches : Single or two level and Unified or split.