1) Processor power

• Selection of the processor is based on the amount of processing power to get the job done and the register width required.
• 8 bit, 16 bit, 32 bit and 64 bit microcontrollers are provided.
• Processing power is different for different microcontrollers.
• High clock, speed and addressing capable microcontrollers are available.
• Very powerful DSPS are available for real time analysis of audio and video signals.

2) Memory

• Designer has to make an estimate of the memory requirement and must make provision for expansion.
• In a system, there are different types of memories : RAM, ROM, EPROM, PROM, etc.
• Secondary storage devices like HDD can be embedded into the system like mobile.
• Flash memory can be used instead of secondary memory. Hence, we can load NT in embedded system. E.g. Embedded Linux OS can be loaded into wristwatches.

3) Operating system

• In desktop, the selection of O.S. is limited.
• In embedded system, a variety of operating systems are available which can be ported into the embedded system.
• It is categorized as follows : Embedded OS, real time OS and mobile OS.
• These operating systems occupy less area in memory than desktop.
• For real time applications, we should use real time OS.
• We can develop our own OS kernel.
• We can use open source OS like Linux. This OS is free and can be customized.

4) Reliability

• Embedded system often reside in machines that are expected to run continuously for years without errors and in some cases recover by themselves, if an error occurs.
• So, the software is usually developed and tested more carefully than that for personal computers and unreliable moving parts such as disk drives, switches or buttons are avoided.

5) Unit cost

• The monetary cost of manufacturing each copy of the system, excluding NRE cost.

6) NRE cost

• The monetary cost of designing the system. Once the system is designed, any number of units can be manufactured without incurring any additional design cost (hence the term “non-recurring”).

7) Size

• The physical space required by the system, often measured in bytes for software, and gates or transistors for hardware.

8) Performance

• The execution time or throughput of the system.

9) Power

• The amount of power consumed by the system, which determines the lifetime of a battery, or the cooling requirements of the IC, since more power means more heat.

10 ) Flexibility

• The ability to change the functionality of the system without incurring heavy NRE cost. Software is typically considered very flexible.

11) Time to market

• The amount of time required to design and manufacture the system to the point the system can be sold to customers.

12) Time to prototype

• The amount of time to build a working version of the system, which may be bigger or more expensive than the final system implementation, but can be used to verify the system’s usefulness and correctness and to refine the system’s functionality.

13) Correctness

• Our confidence that we have implemented the system’s functionality correctly. We can check the functionality throughout the process of designing the system and we can insert test circuitry to check that manufacturing was correct.

14) Safety

• The probability that the system will not cause harm.