Memory And Input/Output Devices

Memory

Memory serves processor short and long-term information storage requirements while registers serve the processor’s short-term storage requirements. Both the program and the data are stored in the memory. This is known as Princeton Architecture where the data and program occupy the same memory. In Harvard Architecture the program and the data occupy separate memory blocks. The former leads to simpler architecture. The later needs two separate connections and hence the data and program can be made parallel leading to parallel processing. The general purpose processors have the Princeton Architecture.

The memory may be Read-Only-Memory or Random Access Memory (RAM). It may exist on the same chip with the processor itself or may exist outside the chip. The on-chip memory is faster than the off-chip memory. To reduce the access (read-write) time a local copy of a portion of memory can be kept in a small but fast memory called the cache memory. The memory also can be categorized as Dynamic or Static. Dynamic memory dissipate less power and hence can be compact and cheaper. But the access time of these memories are slower than their Static counter parts. In Dynamic RAMs (or DRAM) the data is retained by periodic refreshing operation. While in the Static Memory (SRAM) the data is retained continuously. SRAMs are much faster than DRAMs but consume more power. The intermediate cache memory is an SRAM.

In a typical processor when the CPU needs data, it first looks in its own data registers. If the data isn't there, the CPU looks to see if it's in the nearby Level 1 cache. If that fails, it's off to the Level 2 cache. If it's nowhere in cache, the CPU looks in main memory. Not there? The CPU gets it from disk. All the while, the clock is ticking, and the CPU is sitting there waiting.


Input/Output Devices and Interface Chips

Typical RTES interact with the environment and users through some inbuilt hardware. Occasionally external circuits are required for communicating with user, other computers or a network.

In the mobile handset discussed earlier the input output devices are, keyboard, the display screen, the antenna, the microphone, speaker, LED indicators etc. The signal to these units may be analog or digital in nature. To generate an analog signal from the microprocessor we need an Digital to Analog Converter(DAC) and to accept analog signal we need and Analog to Digital Converter (ADC). These DAC and ADC again have certain control modes. They may also operate at different speed than the microprocessor. To synchronize and control these interface chips we may need another interface chip. Similarly we may have interface chips for keyboard, screen and antenna. These chips serve as relaying units to transfer data between the processor and input/output devices. The input/output devices are generally slower than the processor. Therefore, the processor may have to wait till they respond to any request for data transfer. Number of idle clock cycles may be wasted for doing so. However, the input-output interface chips carry out this task without making the processor to wait or idle.



information shared by www.irvs.info