On the other hand a desktop computer may contain all these units on a single Power Circuit Board (PCB) called as the Mother Board. Since these computers handle much larger dimension of data as compared to the embedded systems there has to be elaborate arrangements for storage and faster data transfer between the CPU and memory, CPU and input/output devices and memory and input/output devices. The storage is accomplished by cheaper secondary memories like Hard Disks and CDROM drives. The data transfer process is improved by incorporating multi-level cache and direct memory access methods. Generally no such arrangements are necessary for embedded systems. Because of the number of heterogeneous components in a desktop computer the power supply is required at multiple voltage-levels (typically ±12, ± 5, ± 3, 25 volts). On the other hand an Embedded Systems chip may just need one level DC power supply (typically +5V).
In a desktop computer various units operate at different speeds. Even the units inside a typical CPU such as Pentium-IV may operate at different speeds. The timing and control units are complex and provide multi-phase clock signal to the CPU and other peripherals at different voltage levels. The timing and control unit for an Embedded system may be much simpler.
The typical structure of an embedded system is shown in Fig. 3.2. This can be compared with that of a Desktop Computer as shown in Fig. 3.3. Normally in an embedded system the primary memory, central processing unit and many peripheral components including analog-to-digital converters are housed on a single chip. These single chips are called as Microcontrollers. This is shown by dotted lines in Fig. 3.2.
The typical structure of an Embedded System
(Fig. 3.2)
The structural layout of a desktop Computer
(Fig. 3.3)
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