Questions about GTX 660 Memory Bus Width

[Kipas39]

As we all know, GTX 660 has a unique memory bus width.

At official Techpowerup page of GTX 660, we can see that bus width is 192 Bit, and Bandwidth: 144.2 GB/s

NVIDIA GeForce GTX 660 Specs

NVIDIA GK106, 1032 MHz, 960 Cores, 80 TMUs, 24 ROPs, 2048 MB GDDR5, 1502 MHz, 192 bit

www.techpowerup.com

But, in tab "Card Notes" we see that info:
Bandwidth: 96.1 GB/s+48.1 GB/s
Bus Width: 128 Bit +64 Bit

I imagine it works like, 1.5GB is working in 128 Bit and max bandwidth 96.1 GB/s, when VRAM usage rises above 1.5 GB, last 0.5GB works in 64 Bit and Bandwidth 48.1 GB/s.
But on the other side, I read a couple threads where it says that 1.5 GB works in 192 Bit, with bandwidth 144.2 GB/s, but when VRAM usage above 1.5 GB, last 0.5 GB works in 64 Bit.

So I want to know, where is the truth and what bandwidth speeds are real, and is that the same situation with the GTX 670.

 

[Onasi]

The 660Ti uses the same approach and its mechanism was described in the AnandTech review back in the day:

The GeForce GTX 660 Ti Review, Feat. EVGA, Zotac, and Gigabyte

www.anandtech.com

 

[Kipas39]

The 660Ti uses the same approach and its mechanism was described in the AnandTech review back in the day:

The GeForce GTX 660 Ti Review, Feat. EVGA, Zotac, and Gigabyte

www.anandtech.com

Ok so 660 and 660 Ti have 4 memory controllers, and 1.5 GB are connected to 3. Each controller means 64 bit width, so 192 Bit for 1.5 GB, and last 0.5 GB connected to one controller, so it's 64 Bit.
But i don't understand that image
Why there "2GB modules"

 

[sLowEnd]

Ok so 660 and 660 Ti have 4 memory controllers, and 1.5 GB are connected to 3. Each controller means 64 bit width, so 192 Bit for 1.5 GB, and last 0.5 GB connected to one controller, so it's 64 Bit.
But i don't understand that image
Why there "2GB modules"

2 gigabit.

There are 8 bits in a byte, so:

2048 megabits/8bits= 256 megabytes per memory chip * 8 chips = 2048 megabytes (2 gigabytes) of memory

 

[Kipas39]

2 gigabit.

There are 8 bits in a byte, so:

2048 megabits/8bits= 256 megabytes per memory chip * 8 chips = 2048 megabytes (2 gigabytes) of memory

My bad tottaly forgot that for bits are using small letter.

But i have another question, so if 4 chips instead of 2 attached to one of the memory controllers, how it's possible when controllers are 64 bits only, its mean that theese 2 chips are connected to controller by same lanes as other 2 are connected ?
And it works like 3.5GB and 512 MB segments like in GTX 970, when read and write operations can be done only on one segment at a time ?

I read this article about 970 https://www.anandtech.com/show/8935...cting-the-specs-exploring-memory-allocation/2
Thx for article about 660 Ti, I trying to understand all this stuff more than 8 hrs.