I'm doing fine with a Microsoft Surface 3 tablet. I have the 4GB RAM/128GB SSD version.

This isn't an extremely powerful computer, but it's doing fine running Cubase 8.5 Pro. I wondered if it would be powerful enough when I bought it, but so far everything including audio processing is fast enough that I never start thinking that I need something more powerful.

You can see the technical specs for it at the link.

This does require more details on what you plan on running. VST/pliugins/etc will have their own requirements and may themselves tax resources. The DAW, if any, you plan on running has its own requirements. Audio? Just MIDI? etc.

I thought about a iPad Pro 12",I'm new to this,

I've been following BM replies to "urgent" post.i do intend on a computer based studio like setup,BM made a comment about low latency ASIO.is that a MAC problem or just related to how the questioner was setting up?thanks

I do intend using montage connect

I have used windows OS for over 20 odd years and have recently switch to apple OS X for about 4yrs, I have found that apple Macs core Audio are less problematic than windows base system.

For instance I had DAW studio One and was using it on a Windows base system one of the MIDI plugins called Mojito used with the Akai MPK 49 sounded mechanical or like a toy you had to do a lot of tweaking to make it sound realistic. I went with the Mac book pro with the same DAW Studio one with Mojito and the sound greatly improved over the window base system.

In my own opinion i would highly recommend OS X
Note if you notice when viewing people online DAW setup you will see the Majority using Macs or apple products. Both have there strength and weaknesses.

ASIO low latency is dealing with response time/travel. ASIO was created by Steinberg for window base systems due to high latency issues that windows OS had and to resolve audio problems of the OS for their DAW Cubase. ASIO was never a Mac problem. Here is a link to educate yourself on ASIO https://en.wikipedia.org/wiki/Audio_Stream_Input/Output .

Recommend specs Mac or PC base systems
8 or 16 GB
CPU 2 ghz above

Hard minimum 500 gb recommend 1TB or 2TB best: SSD drive you can partition the 1TB or 2TB to allow quicker booting of OS/OS X and store projects or loops and sample on other partition, note if you do not partition your projects, samples and loops = (DATA) you collect will use up storage this will slow down OS/OS X boot time.
If you go with the 500 GB recommend that you purchase a SSD later it has no moving parts like hard drives write and read. This will allow you to access Loops,samples and projects on the other partition without bottle necks/Freezing (write and read).

Also if you can get one that can be upgraded internal Hard drive/SSD and Memory/Ram. If you purchase a tablet or iPad be aware you are stuck with what you purchase you can't upgrade the Storage or Ram. Apple products you have to buy extra accessories vs windows you may not have to except maybe a USB powered Hub.

Thankyou so much for your help and the info.

I still think it would help to know what software you are planning to run on the Mac or PC.

Cubase and most all other software published the minimum/recommended system requirements. Example:

https://www.steinberg.net/en/products/cubase/resources.html

Which shows (recommended):

64-bit Intel/AMD multi-core CPU (Intel i5, i7, or better)

8GB RAM

12GB HDD space (or 18GB for the Pro version, 12GB is for the free version that, in v8.5 - not 9 as the link, comes with Montage )

1920x1080 resolution

Windows PC consideration (not Mac): Graphics card w/DirectX 10 and WDDM 1.1 support

Other software you plan on running will have its own set of requirements - so go through this exercise with all packages you plan on possibly using.

When it comes to low latency, please recognize that to playback music, the concept of latency is not really an issue. So consumer Music on computers puts very little demand on the CPU. Musicians requirements are far, far more severe, and require/demand the best timing possible. Consumer drivers may have several hundreds of millisecond delays, but this is not critical to the listener.

Your DAW can compensate for the time gap between you pressing a key and the time it took to play you the audio. It can time stamp and align the incoming signal precisely with the played back audio. Obviously for the musician lower is better.

It is an issue for musicians who need to listen and play along (at the same time). If you send signal into a computer it takes some amount of time to process and return the signal - this impacts your ability to monitor yourself through the computer. If there is too much latency monitoring this 'delayed' signal can disturb you ability to perform.

The latency becomes an issue when you attempt to listen to yourself "through" the computer... that time it takes to Receive, register/time stamp, and playback is the latency. When your synth or processor is external hardware, you can and often do, opt to monitor yourself DIRECT.

Direct Monitoring creates is a situation where you are hearing your own performance before it traverses the computer. It's a zero latency situation. This luxury means you can record with your hardware's effects without having to be on the downwind side of computer processing (latency). You can see how if the effects are on the computer monitoring them in real time is a problem (processing takes time).

So even if your computer is not the speediest in the world, and your latency numbers are not optimum, you can opt to work to never have to be on the bad side of latent signal. This is the case because you have the option of Direct Monitor routing.

The Montage is as at home with a PC as with a Mac, you can also plug direct to an iOS device. One is not easier to work than the other, one is not better than the other, they all have learning curves and advantages and disadvantages. Use what make you most comfortable.

The most important things for a music computer.

Futureproofing: Make sure you get a computer that will last for a while, this will save you money in the long run. So spend a little extra.
CPU: Processor with fast Cores. Latest generation Kaby Lake processors, like the Intel Core i7-7700, or Intel Core i5-7600 are superb.
RAM: More ram means more space for sampled tracks and plugins. 16 GB is pretty good, go 32 GB if your projects are big.
Harddrive: SSD drive as your OS and music driver. SSD's are faster, and is important when you playback large projects.
Backup: Get a backup solution. Skydrive or google drive might do it. Depending on your computer of choice. Mirror two SSD's in Raid. If one breaks down, you can still boot on the second SSD.
Noise: Make sure the computer is silent. This depends on the CPU cooling solution and fans in the chassis. Usually replaceable.
Connectivity: Make sure you get the latest ports like Thunderbolt 3 and USB 3.1 2nd gen. It's good futureproofing.

Cost, maybe ~ 1500$ - 2000$

As for MAC's. Tim Cook have said in the developers forums that there will be new Macs in 2017. Personally I wait for this.

In the studio, a quiet computer may make sense. If you tour and your computer is used as part of your live sound (VSTi, effects, etc) - then portability may be more important. There are two forms of quiet - 1) how much noise the fans and hard disks make as well as 2) radiated energy at frequencies to interfere with other audio equipment. #2 would be important for live or studio although this is difficult to ascertain and usually would boil down to both minimizing wireless devices as well as taking a look for certifications (FCC level passed and the like). Some international certifications cover decibel restrictions (audible noise level) as well as more stringent radiated energy emission requirements than FCC.

Although the Montage itself may have fairly "low" requirements to make it integrate with a computer (relative to an engineering workstation, for example) - all the rest of your demands (which are not stated) may have an impact on what to purchase.