Product
Vivo X21 UD
Vivo X21 UD
Xiaomi Mi 9T
Xiaomi Mi 9T
Battery
Charging 18W wired 18W wired
Type Li-Ion 3200 mAh, non-removable Li-Po 4000 mAh, non-removable
Body
Build Glass front (Gorilla Glass 3), aluminum back, aluminum frame Glass front (Gorilla Glass 5), glass back, aluminum frame
Dimensions 154.5 x 74.8 x 7.4 mm (6.08 x 2.94 x 0.29 in) 156.7 x 74.3 x 8.8 mm (6.17 x 2.93 x 0.35 in)
SIM Nano-SIM + Nano-SIM Nano-SIM + Nano-SIM
Weight 156.2 g (5.50 oz) 191 g (6.74 oz)
Comms
Bluetooth 5.0, A2DP, LE 5.0, A2DP, LE, aptX HD
NFC No Yes
Positioning GPS, GLONASS GPS, GLONASS, GALILEO, BDS
Radio FM radio FM radio
USB microUSB 2.0, OTG USB Type-C 2.0, OTG
WLAN Wi-Fi 802.11 a/b/g/n/ac, dual-band, Wi-Fi Direct Wi-Fi 802.11 a/b/g/n/ac, dual-band, Wi-Fi Direct
Display
Protection Corning Gorilla Glass 3 Corning Gorilla Glass 5
Resolution 1080 x 2280 pixels, 19:9 ratio (~402 ppi density) 1080 x 2340 pixels, 19.5:9 ratio (~403 ppi density)
Size 6.28 inches, 98.4 cm2 (~85.2% screen-to-body ratio) 6.39 inches, 100.2 cm2 (~86.1% screen-to-body ratio)
Type Super AMOLED AMOLED, HDR
Features
Sensors Fingerprint (under display, optical), accelerometer, proximity, compass Fingerprint (under display, optical), accelerometer, gyro, proximity, compass
Launch
Announced 2018, March. Released 2018, March 2019, June 12. Released 2019, June 12
Status Discontinued Discontinued
Main Camera
Dual 12 MP, f/1.8, 1/2.55", 1.4µm, dual pixel PDAF 5 MP, f/2.4, (depth) -
Features LED flash, HDR, panorama Dual-LED flash, HDR, panorama
Triple - 48 MP, f/1.8, 26mm (wide), 1/2.0", 0.8µm, PDAF 8 MP, f/2.4, 53mm (telephoto), 1/4.0", 1.12µm, PDAF, 2x optical zoom 13 MP, f/2.4, 12mm (ultrawide), 1/3.1", 1.12µm
Video 1080p@30fps 4K@30fps, 1080p@30/120/240fps, 1080p@960fps
Memory
Card slot microSDXC (uses shared SIM slot) No
Internal 128GB 6GB RAM 64GB 6GB RAM, 128GB 6GB RAM, 256GB 8GB RAM
  eMMC 5.1 UFS 2.0
Misc
Colors Black, Ruby Red Carbon black, Red flame, Glacier blue
Models X21UD A M1903F10G
SAR - 1.19 W/kg (head)     1.18 W/kg (body)    
SAR EU - 1.34 W/kg (head)     1.51 W/kg (body)    
Network
2G bands GSM 850 / 900 / 1800 / 1900 GSM 850 / 900 / 1800 / 1900
3G bands HSDPA 850 / 900 / 1900 / 2100 HSDPA 850 / 900 / 1700(AWS) / 1900 / 2100
4G bands 1, 2, 3, 5, 8, 34, 38, 39, 40, 41 1, 2, 3, 4, 5, 7, 8, 20, 28, 38, 40
Speed HSPA 42.2/5.76 Mbps, LTE (2CA) Cat6 300/50 Mbps HSPA, LTE
Technology GSM / CDMA / HSPA / LTE GSM / HSPA / LTE
  CDMA 800 & TD-SCDMA -
Our Tests
Audio quality - Noise -93.5dB / Crosstalk -93.8dB
Battery (old) - Endurance rating 100h
Camera - Photo / Video
Display - 646 nits max brightness (measured)
Loudspeaker - -25.3 LUFS (Very good)
Performance - AnTuTu: 211915 (v7), 257146 (v8) GeekBench: 6863 (v4.4), 1703 (v5.1) GFXBench: 13fps (ES 3.1 onscreen)
Platform
Chipset Qualcomm SDM660 Snapdragon 660 (14 nm) Qualcomm SDM730 Snapdragon 730 (8 nm)
CPU Octa-core (4x2.2 GHz Kryo 260 Gold & 4x1.8 GHz Kryo 260 Silver) Octa-core (2x2.2 GHz Kryo 470 Gold & 6x1.8 GHz Kryo 470 Silver)
GPU Adreno 512 Adreno 618
OS Android 8.1 (Oreo), Funtouch 4 Android 9.0 (Pie), upgradable to Android 11, MIUI 12.1
Selfie camera
Features - HDR
Single 12 MP, f/2.0, (wide), 1/2.8", 1.28µm Motorized pop-up 20 MP, f/2.2, (wide), 1/3.4", 0.8µm
Video 1080p@30fps 1080p@30fps
Sound
3.5mm jack Yes Yes
Loudspeaker Yes Yes
  32-bit/192kHz Hi-Res audio 24-bit/192kHz Hi-Res audio