Most of the current smartphones on the market contain Qualcomm CPU. The most common chips used in budget phones are MSM7x25 and MSM7x27. They are available in two variants for different GSM/CDMA networks.
Network support is distinguished by model number, by its 2nd digit:
- 2: GSM only
- 6: GSM + CDMA for chinese market (more precisely CDMA 1x EV-DO rev A and WCDMA)
All the chips contain ARM1136 variant of ARM11 core and use ARMv6 instruction set. At the first look to GSM specifications at PDAdb.net, you get false impression that there is no difference except of clock:
- MSM7x25: 528MHz, 16+16kB Ll cache
- MSM7x27: 600MHz, 16+16kB L1 cache
When you ask users (or have look into internet forums), you get complete opposite feedback. MSM7x25 usersare complaining about speed, incapability of playing AngryBirds and other games, but MSM7x27 users hardly ever complain.
How is this possible? Comparing clocks, there is only 13% increment – can this be a key to better performance? No!
I have been searching answer , and finally I found it in Qualcomm specifications.
(Most people including XDA developers forum members failed to find this, as there are no MSM7225 documents on Qualcomm site and even Google doesn’t give you relevant results. I was lucky: Chinese Baidu search engine gave me an answer.)
source: 80-VM151-21 MSM7627 CHIPSET TRAINING INTRODUCTION AND CHIPSET OVERVIEW
As you can see, there ARE differences! Most important improvements of MSM7x27 over MSM7x25 are:
- Adreno 200 GPU embedded
- L2 cache (256kB)
- faster DSP by 25%
- RAM access 20% faster
Now it is clear: L2 cache and faster RAM improves performance by 10-30% (est.) Adreno GPU is the reason why MSM7x27 users can play Angry Birds and even Angry Birds Rio. And faster DSP is responsible for smooth video playing.
Note, that there are even MSM7x27-1 CPU available, sometimes called MSM7x27T or MSM7x27 Turbo, with 800MHz clock. Higher clock is allowed either by improved manufacturing process (but still on 65nm) or by die harvesting. MSM7x27 chips can be overclocked to 700-850MHz as you can see in Smartphone Benchmarks.
Qualcomm MSM7x27 is not only higher clocked variant of MSM7x25, but it is seriously improved. And remember: MSM7x25 does not contain any GPU at all – all OpenGL operations then have to be performed by slow SW emulation in main CPU, using Pixel Flinger SW emulator.
So there is one simple advice: Avoid buing phones using MSM7x25 CPU.
Sources: Wikipedia, Baidu, Qualcomm press release an more.