From www.army-technology.com:
The T-90S is the latest development in the T-series of Russian tanks and represents an increase in firepower, mobility and protection. It is manufactured by Nizhnyi Tagil of the Russian Federation.
The T-90S is in service with the Russian Army and the Indian Army. In February 2001, the Indian Army signed a contract for 310 T-90S tanks. 124 were completed in Russia and the rest are being delivered in "knocked down/semi-knocked down" form for final assembly in India. The first of these was delivered in January 2004. The locally-assembled tanks are christened "Bhishma". The tanks are fitted with the Shtora self-protection system and thermal imagers from Thales of France and Peleng of Belarus.
ARMAMENT
The T-90S armament includes one 125mm 2A46M smoothbore gun, stabilised in two axes and fitted with a thermal sleeve. The gun tube can be replaced without dismantling inside the turret. The gun can fire a variety of ammunition including APDS (Armour Piercing Discarding Sabot), HEAT (High Explosive Anti-Tank), HE-FRAG (High Explosive Fragmentation) as well as shrapnel projectiles with time fuzes.
The T-90S gun can also fire the 9M119 Refleks (NATO designation AT-11 Sniper) anti-tank guided missile system. The range of the missile is 100m to 4,000m and takes 11.7 sec to reach maximum range. The system is intended to engage tanks fitted with ERA (Explosive Reactive Armour) as well as low-flying air targets such as helicopters, at a range of up to 5km. The missile system fires either the 9M119 or 9M119M missiles which have semi-automatic laser beamriding guidance and a hollow charge warhead. Missile weight is 23.4kg. The guns automatic loader will feed both ordnance and missiles.
Also fitted is a coaxial 7.62mm PKT machine gun and a 12.7mm air defence machine gun. A 5.45mm AKS-74 assault rifle is carried on a storage rack.
SELF-PROTECTION
The T-90 tank is protected by both conventional armour-plating and explosive reactive armour (ERA).
The T-90 is fitted with the Shtora-1 defensive aids suite which is produced by Electronintorg of Russia. This system includes infrared jammer, laser warning system with four laser warning receivers, grenade discharging system which produces an aerosol screen and a computerised control system.
It is also fitted with NBC (nuclear, biological and chemical) protection equipment.
FIRE CONTROL AND OBSERVATION
The T-90S has the 1A4GT integrated fire control system (IFCS) which is automatic but with manual override for the commander. The IFCS contains the gunner's 1A43 day fire control system, gunner's TO1-KO1 thermal imaging sight which has a target identification range of 1.2km to 1.5km and commander's PNK-S sight.
The gunner's 1A43 day FCS comprises: 1G46 day sight/rangefinder with missile guidance channel, 2E42-4 armament stabiliser, 1V528 ballistic computer and DVE-BS wind gauge.
The commander's PNK-4S sight includes a TKN-4S (Agat-S) day/night sight which has identification ranges of 800m (day) and 700m (night).
The driver is equipped with a TVN-5 infrared night viewer.
PROPULSION
The T-90S has a liquid-cooled V-84MS 618kW (840 hp) four-stroke V-12 piston engine. This engine can be fuelled by T-2 or TS-1 kerosene and A-72 benzine, in addition to diesel. The tank can carry up to 1,600 litres of fuel in the main fuel tanks and fuel drums. The fuel tanks are reinforced with armour plating.
The tank is provided with a snorkel for deep fording and can ford 5m of water with equipment which can be deployed in 20 minutes.
The mechanical transmission includes primary reduction gear, two planetary final gearboxes and two planetary final drives. The running gear features torsion bar suspension with hydraulic shock absorbers at one, two and six road wheel stations and tracks with rubber-metallic pin hinges.
"The T-90S gun can also fire the 9M119 Refleks (NATO designation AT-11 Sniper) anti-tank guided missile system"
This is an interesting deviation from NATO tanks which cannot fire a ATGM. The US used to have the Sheridan and a version of the M60 with a gun that fired a missile but that weapon system was a big disappointment. THe US and Germany worked on a tank that was suppose to fire a missile but that program, as almost all multinational tank programs was cancelled. The 125 MM gun is larger than the standard 120 MM NATO tank gun. I am not sure if the T90 had special armor like NATO tanks which involve use of ceramics and other materials.