Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 5 down vote favorite

I have been having a hard time trying to know if ARM is a microprocessor or microcontroller or something else?

share|improve this question

3 Answers

up vote 15 down vote accepted

Neither.

ARM is a CPU architecture (more accurate, a family of related CPU architectures). If you put that (or anyother) CPU on a chip all by itself, you have a microprocessor (like they did in the age-old Acorn machines). If you combine it with ROM (Flash), RAM and peripherals on one chip, you have a microcontroller (example: LPC2148).

Things can get a bit muddy when you combine the CPU with ROM and RAM, but also provide the data, address and control lines on the pins, so external memory can be added. Such a chip is can be used either in microcontroller mode, or in microprocessor mode. (example: LPC2478)

Nowadays smaller systems (up to 0.5Mb Flash, a few 10's Kb RAM) are available as microcontroller. Larger systems (typically running a Linux or something similar) are typically composed of a microprocessor with external RAM. (ROM can be external too, or a small boot-rom on chip + an SD card or similar). Examples: open up any mobile phone, set-top box, modem/router, etc.

Funny note: microcontrollers tend to be short on RAM, hence the run from Flash, which often limits their speed. Microprocessors often have plenty RAM, have a slower Flash, which is loaded into RAM for execution.

share|improve this answer
I would suggest that a useful dividing between microprocessors and microcontrollers is to say that the latter have enough stuff on chip to run at least somewhat usefully without any attached RAM or ROM. The only murky cases would be devices which include space for mask ROM, but are frequently sold without any useful code therein. I would regard such devices as microcontrollers if their behavior in use would be essentially indistinguishable from the behavior of one whose mask ROM was "programmed" but externally disabled. – supercat Jun 18 '12 at 15:49
@supercat: My division would not be according to 'how it can be used' but rather to 'how it is used' (or maybe 'how it is intended to be used'). According to you the LPC2478 would be a microcontroller, I consider it a hybrid. – Wouter van Ooijen Jun 18 '12 at 16:06
With 98K of on-board RAM and 512K of on-board flash, it certainly sounds as though it could be quite usefully employed in systems without any external memory; from a quick glance at the data sheet, I would regard that one as being in the "microcontroller" camp, and I wouldn't consider it a close call. – supercat Jun 18 '12 at 16:48
I know you don't, but I do. The chip is (or was) regularly used to run for instance Linux, so I think that although it certainly can be used as a microcontroler, it is not (only) a microcontroler. – Wouter van Ooijen Jun 18 '12 at 17:21
up vote 6 down vote

Neither (and both)

ARM is a company who license CPU cores.

The ARM core can be, and is, used by lots of companies to make both microcontrollers and microprocessors.

share|improve this answer
up vote 6 down vote

Technically, ARM is a microprocessor, or, more specifically, a microprocessor architecture. The thing to understand, though, is that it doesn't represent a physical microprocessor, but the design that allows to build one.

ARM Holdings is a multinational semiconductor group that doesn't manufacture any CPU; instead, they design them and then sell the architecture under licensing. The designs are used to build microprocessors as well as microcontrollers, but what ARM provides is just the core.

It's also wrong to say that it's a microcontroller, because it's the manufacturer that takes the ARM core and build all the peripherals around it.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.