Why do we need different CPU architecture for serv

Question

I was just wondering what other CPU architectures are available other than INTEL & AMD. So, found List of CPU architectures on Wikipedia.

It categorizes notable CPU architectures into following categories.

1. Embedded CPU architectures
2. Microcomputer CPU architectures
3. Workstation/Server CPU architectures
4. Mini/Mainframe CPU architectures
5. Mixed core CPU architectures

I was analyzing their purposes and have few doubts. Taking Microcomputer CPU (PC) architecture as reference and comparing it to others we have:

Embedded CPU architecture:

• They are a completely new world.
• Embedded systems are small & do very specific task mostly real time & low power consuming so we do not need so many & such wide registers available in a microcomputer CPU (typical PC). In other words we do need a new small & tiny architecture. Hence new architecture & new instruction RISC.
• The above point also clarifies why do we need a separate operating system (RTOS).

Workstation/Server CPU architectures

• I don't know what is a workstation. Someone clarify regarding the workstation.
• As of the server. It is dedicated to run a specific software (server software like httpd, mysql etc.). Even if other processes run we need to give server process priority therefore there is a need for new scheduling scheme and thus we need operating system different than general purpose one. If you have any more points for the need of server OS please mention.
• But I don't get why do we need a new CPU Architecture. Why cant Microcomputer CPU architecture do the job. Can someone please clarify?

Mini/Mainframe CPU architectures

• Again I don't know what are these & what miniframes or mainframes used for? I just know they are very big and occupy complete floor. But I never read about some real world problems they are trying to solve. If any one working on one of these. Share your knowledge.
• Can some one clarify its purpose & why is it that microcomputer CPU archicture not suitable for it?
• Is there a new kind of operating system for this too? Why?

Mixed core CPU architectures

• Never heard of these.

If possible please keep your answer in this format:

XYZ CPU architectures

• Purpose of XYZ
• Need for a new architecture. why can't current microcomputer CPU architecture work? They go upto 3GHZ & have upto 8 cores.
• Need for a new Operating System Why do we need a new kind of operating system for this kind of archictures?

EDIT:

Guys, this is not a homework problem. I can't do anything to make you guys believe. I don't know if the question is not clear or something else but I'm only interested in just specific technical details.

Let me put a part of this question in another way. You are in an interview and if the interviewer asks you "tell me, Microcomputer processors are fast & a lot capable and our PC operating systems are good. Why do we need a different architecture like SPARC, Itanium and need a different OS like Windows Server for servers?". What would you answer? I hope got my point.

Answer 1

It seems like your question and goal is really to understand the history of Computer Architecture. If that is true then you need this book. It should help you to gain the understanding that you are looking for:

http://www.amazon.com/Computer-Architecture-Concepts-Evolution-2/dp/0201105578

Dr. Brooks covers the history of computer architecture, the initial appearance of new ideas and traces the development of these ideas through different machines over time.

Answer 2

Workstations are now almost-extinct form of computers. Basically they used to be high-end computers looking like desktops, but with some important differences, such as RISC processors, SCSI drives instead of IDE and running UNIX or (later) NT line of Windows operating systems. Mac Pro can be seen as a present form of workstation.

Mainframes are big (though they do not necessarily occupy whole floor) computers. They provide very high availibility (most parts of a mainframe, including processors and memory, can be replaced without system going down) and backwards compatibility (many modern mainframes can run unmodified software written for '70 mainframes).

The biggest advantage of x86 architecture is compatibility with x86 architecture. CISC is usually considered obsolete, that's why most modern architectures are RISC based. Even new Intel & AMD processors are RISC under the hood.

In the past, gap between home computers and "professional" hardware was much bigger than today, so "microcomputer" hardware was inadequate for servers. When most of RISC "server" architectures (SPARC, PowerPC, MIPS, Alpha) were created, most microcomputer chips were still 16-bit. First 64 bit PC chip (AMD Opteron) shipped over 10 years after MIPS R4000. The same was with operating systems: PC operating systems (DOS and non-NT Windows) simply were inadequate for servers.

In embedded systems, x86 chips are simply not enough power efficient. ARM processors provide comparable processing power using much less energy.