smart phone

<1> Guide to smartphone hardware (3/7): Memory and Storage [Mar 12, 2012] -

System On a Chip (SoC)

RAM -

Size -512MB is pretty enough.  Speed - smartphone SoCs mostly use LPDDR2, where the “LP” stands for low-power. LPDDR2 is mostly similar to standard DDR2 except that it uses less power (hence the name) which does degrade performance. DDR3 interfacing capabilities will be introduced in upcoming smartphone SoCs.  Channel - Memory channels do little in real-world performance to improve the speed of a RAM set-up.

The iPhone 4S has 512 MB of LPDDR2 embedded inside the A5 SoC. 

Internal storage and ROM - internal storage is critical to a smartphone's operation; without any place to store the operating system and critical files there would be nothing for the phone to do. Even if a phone has no storage accessible to the user, there will also be some form of internal storage that stores the operating system.

multiple storage chips : (1) ROM - stores the system files; (2) Others - stores applications, for cache, etc.

classification of the internal storage: (1) user accessible ; (2) non-user-accessible, for system files and (non-movable? not allow to delete/uninstall?) applications.

Some devices, such as the Samsung Galaxy S, have a multi-ROM set-up. One memory chip is smaller around 512 MB, but faster, and stores the main system files, cache and application data in separate partitions. The second chip is larger, and is usually a 1-2 GB partition of the user storage that is slower but allows for storage of applications.

Other devices such as the Apple iPhone 4S and Motorola Droid Razr prefer to include just one storage chip that sits, in terms of performance, between the two chips used in a multi-chip set-up. The phone may be stated to include 16 GB of internal storage, but after a 1-2 GB system partition and (in the case of the Razr) a 4 GB application partition the user accessible storage may end up as low as 8 GB. 

Performance of internal storage chips are, generally speaking, better than you would achieve with external microSD cards.

User removable storage - 

Out of the three major smartphone operating systems (iOS, Android and WP7), Android is the only one that really supports removable storage. 

When it comes to Android there are two implementations of user removable storage: it’s either the only user accessible storage or it complements the internal user accessible storage. If it complements what is already available, there will be a separate system partition for the external card such as /sd-ext or /mmc that some applications, such as music and video players, can access. Often applications that download data to the “SD card” will actually download to the internal storage in situations where there are both available (unless there is an option). [tsiu: so not really only to SD card but download to both internal storage and the card.]

SDXC cards are not supported in most new smartphones, meaning the maximum expansion of storage rests at 32 GB.

With the right combination of a device with 64 GB of internal storage with a microSD card slot, such as the Samsung Galaxy Tab 7.7, you could potentially have 96 GB of user accessible storage if you added in a 32 GB microSD card.

src

My Note:
<1> RAM on smartphone = RAM on PC.  Internal storage on smartphone = C drive on PC.  On PC, 4GB RAM is minimum; and 128GB SSD is comfortable for Win 7.  My another PC which uses an only 40GB SSD as the OS drive is handicapped. 
<2> Suggestion:  buy Redmi Note 2 Prime (32GB internal storage).      

<2>

Cloud Storage

To overcome the problem of reduced internal storage space, several high-end smartphones are sold with free cloud storage accounts. This could be 10, 20 or even 50GB. Whilst this is a nice extra, bear in mind that not all data and files can be saved to cloud storage (apps for example). You will also be unable to access files stored in the cloud if you do not have a Wi-Fi or mobile data connection.   src

<3> my_xiaomi.htm

Redmi Note 2 :

Full Spec: <1>    Review: <1>

Redmi Note 3 (MediaTek):

Full Spec: <1> - 3GB RAM

Don't Buy.  Instead, buy Redmi Note 2 Prime or Redmi 3 (has a microSD slot for up to 128GB of additional storage; a 5in HD screen).  But Redmi 3 uses Non-removable Li-Ion 4100 mAh battery.  So my preference is:

 Redmi Note 2 Prime > Redmi 3 > Redmi Note 3.  How about Redmi 2?

Src: http://www.gsmarena.com/compare.php3?idPhone1=7769&idPhone2=7862&sSearch3=&idPhone3=6992

4G LTE

4G LTE is the most advanced in terms of speed. The general claim is that 4G LTE networks can download data at speeds between 5 and 12 megabits per second.

In comparison, the realistic download speeds for 4G networks can range anywhere from 3 to 8 megabits per second, depending on congestion, the wireless carrier and the specific technology the company has used for its data network. The older 3G networks can typically download data around 800 to 950 kilobits per second.  src

The different LTE frequencies and bands used in different countries will mean that only multi-band phones will be able to use LTE in all countries where it is supported.   wiki

Redmi 2 - supports 4G, and in particular LTE bands 3, 7 and 8 on the FDD LTE standard. This means the phone will be able to use 4G in markets such as UK and Australia but not in the US.

http://www.pcmag.com/article2/0,2817,2498615,00.asp  FEBRUARY 1, 2016

US Mobile, which uses T-Mobile's network, is selling, servicing, and supporting a few Xiaomi and Meizu phones as of last night.

The phones going on sale include the Xiaomi Redmi 2 for $119, the Xiaomi Mi 3 for $135, the Meizu Note 2 for $149, and the Xiaomi Mi 4 for $219. 

There are some down sides to these new phones. Most notably, the phones can't get LTE in the U.S. They just weren't designed for our networks, and they don't have U.S.-compatible 4G bands.

[Tsiu : It doesn't matter.  In US, mostly I use WiFi.  And I can still use 3G.  So no 4G is bearable.  In HK, I probably only use 3G service too.]

http://www.androidcentral.com/unlocked-phones-europe  (June 2015)

As mentioned in the article, in the USA, for a phone to just be unlocked is not sufficient due to the many different LTE bands used by the different carriers, often exclusively so.

A good example are devices sold by Verizon, the largest of all the US carriers. ALL of Verizon's LTE devices are unlocked (regardless of whether they are purchased under contract or not). However, a typical Verizon device might not work well on the other 3 nationwide carriers as most Verizon devices lack bands to support those other carriers. So, a typical Verizon phone used on SEE BELOW will not support the following:

AT&T (missing bands 17, 29 and 30; will support bands 2, 4 and 5)
T-Mobile (missing band 12; will support bands 2 and 4)
Sprint (missing bands 25, 26 and 41, will not support any of Sprint's current LTE bands)

Tsiu: 

A typical Verizon unlocked phone might get AT&T service if the service is of bands 2, 4 and 5.  If your area is of bands 17, 29 and 30, then no AT&T signal.  

A typical Verizon unlocked phone might get T-Mobile service if the service is of bands 2 and 4.  If your area is of bands 12, then no T-mobile signal. 

When Winnie switches from T-Mobile to TracFone, go to the web site to make sure the T-Mobile Prism II is supported by TracFone in the area.

Plan:

10 alternatives (MVNOs):  TracFone/Net10, UltraMobile

Xiaomi Redmi Note 2 - Specifications :  http://www.devicespecifications.com/en/model/848e3256

Wi-Fi: n 5GHz, ac, Dual band, Wi-Fi Hotspot, Wi-Fi Direct, Wi-Fi Display

Xiaomi Redmi Note 4X

Xiaomi Redmi Note 4X: http://www.devicespecifications.com/en/model/9910413e

Wi-Fi: n 5GHz, Dual band, Wi-Fi Hotspot, Wi-Fi Direct, Wi-Fi Display

http://c.mi.com/thread-48836-1-1.html : 100 % working solution for stuck at 2G problem! ... This occurs mostly in MIUI 8. A bug  ...

Winnie tried her new phone with 4G LTE (Access Point Name = fast.tmobile.com).  Internet very fast.  Outgoing call is good because it can go through her data cellular network.  But can't receive incoming call. 

Then trying 2G (EDGE).  All works but Internet slow. 

Then trying 3G with setting APN=epc.tmobile.com.  All good.

T-Mobile APN Settings 2017

Which bands does T-Mobile use?

T-Mobile still supports one 2G band, but like other carriers are primarily focusing on LTE (4G) deployment.

2G bands (EDGE)

• 2

3G bands

• 4
• 2

LTE (4G) bands

• 12
• 4
• 2

TracFone T-mobile compatibility alert:

In order to connect to the TracFone 4G LTE network, your device must operate on Band II, IV or in certain areas, Band 12. For 3G or other 4G service, your device must operate on Band II (1900 MHz) or IV (1700/2100 MHz). GSM devices that do not support these bands may operate at 2G (EDGE) speeds.

歐普瑞斯 紅米 note 4x 手機皮套 手機套 保護殼 支架 紅米note4x 保護套 手機殼 外殼 軌跡系列

http://feebee.com.tw/bid/%E7%B4%85%E7%B1%B3Note%204X%20%E4%BF%9D%E8%AD%B7%E5%A5%97/?page=48&sort=rp&mode=l?page=48&skip=m

Mobal^® International Cell Phone

• Frequency Bands:
  2G Bands: GSM 850/900/1800/1900
• 3G/UMTS: Band1(2100),Band2(1900),Band9(1700),Band41700/2100,Band8(900),Band5(850)
• 4G/LTE: Band1(LTE2100),Band2(LTE1900),Band3(LTE1800),Band4(LTE1700/2100),Band7(LTE2600),Band12(LTE700),Band17(LTE700),Band28(LTE700)

• Carrier          4G LTE Bands       Frequencies AT&T             2, 4, 5, 17        1900, 1700 abcde, 700 bc Verizon Wireless 2, 4, 13           1900, 1700 f, 700 c T-Mobile         2, 4, 12, 66, 71** 1900, 1700 def, 700 a, 600 Sprint           25, 26, 41         1900 g, 850, 2500 Europe           3, 7, 20           1800, 2600, 800 China, India     40, 41             2300, 2500 *Main band for each carrier is marked in bold. **Rolling out in 2017.

https://www.internationalstudent.com/international-communications/sim-card/

Some companies that offer international cell phone rentals are:

• STATravel
• Mobal
• OneSIM

My ideal smartphone (10/2017):

1. One for all - talk/text/Internet.  NYC and Hong Kong.

2. Internet at 4G LTE in both NY & HK.  3.5G/3G is acceptable.  2G is not desirable.

3. Not expensive.  < US$300.  iPhone is not desirable.

4. Reasonable strong spec:  2GB RAM.  16GB Internal Memory.  To allow installing a large number of apps, 32GB is better.  Support SD (iPhone not again).  Good camera.  

5. 5.5".  4" is too small.

Alert: Don't buy phone in US and intend to use in HK unless it is absolutely confirmed that it can be used in HK.  T-Mobile Prism II is already an excellent lesson for me. Don't repeat the same mistake again.

Possible Candidates:

C1.  Redmi Note 4X (Winnie's phone)

       - use Cricket Wireless / AT&T.  Cricket is expensive if not with Rita's Group Save discount. 

       - use TracFone AT&T Compatible 4G LTE Dual SIM Card.  Hopefully I can get 3.5G from it.

https://www.frequencycheck.com/carrier-compatibility/e3O5TY/xiaomi-mi5-4g-lte-a-64gb-xiaomi-libra/at-t-united-states :  Xiaomi Mi5 4G LTE-A 64GB (Xiaomi Libra) is compatible with 4 out of 8 bands on AT&T (United States). 

https://www.frequencycheck.com/compatibility/4kVvir8/xiaomi-hongmi-note-2-redmi-note-2-dual-sim-td-lte-20150718/united-states : really?  Boost Mobile - CDMA - 4G LTE is compatible with my device?

Xiaomi Redmi Note 7

https://www.gsmarena.com/xiaomi_redmi_note_7-9513.php

6GB+64GB  ¥1399元

4GB+64GB  ¥1199元

3GB+32GB  ¥999元