While the movie industry loves embellishing the world of espionage to the point of global destruction, some of its most recognizable tropes are, in fact, based in reality. One of the most common sights in espionage and thriller movies is the silenced pistol. Able to magically kill over a distance of several meters without anyone in the vicinity noticing, this trope endures.
It's also based in reality. In reality, they're not called 'silencers' by the armorer, they're called suppressors in recognition of the fact that they certainly don't silence the shot. They were originally invented for the much more sporting purpose of game hunting - with a suppressor fitted to your rifle, the odds of spooking all the game in a wide area each time you fire go way down.
One other standard trope - the suppressor is attached to the front of the weapon's barrel. Usually it is screwed on to threads in the barrel end; sometimes it is attached to the slide or frame. It is generally shown as a cylinder (or angular oblong) which extends the barrel. This, too, is accurate - suppressors of this type are readily available in sporting goods stores around the world, assuming the local laws permit it (and yes, you can buy them in the United States, if you live in a state that allows it and are willing to pay the ATF some tax stamp money).
But there are problems. Most notably, the applique suppressor is big and it makes the gun longer. The effectiveness of the suppressor is linked to its length, or at least the length of its gas trap - so making it shorter makes it less effective. This tends to disturb the balance of the pistol (unless it was designed to be balanced with an attached suppressor) as well as make it much harder to conceal. In addition, some suppressors, in screwing on to the barrel, lock the slide - which means the gun becomes a single-shot. This can be mitigated by having the barrel extend forward of the slide, but the mechanical action of a gun firing is surprisingly loud - it's metal slamming around at high speed - so sometimes it's not worth it.
And finally, the point of the writeup.
The spiritual descendants of Felix Dzerzhinsky had a need for a small, handy, discreet firearm. As the real-life version of the SMERSH that James Bond faced, and the rest of the internal secret police organization and their cousins/deadly enemies at the GRU, the silenced pistol was a tool of the trade. And because the Soviet Union was nothing if not fiendishly inventive, especially around weapons technology, they had a whole range of weapons expressly designed for this job.
These were integrally suppressed guns, like the British de Lisle Carbine - a firearm with its suppressing tech built in, not screwed on to the front. In the early versions, like the PB pistol, this consisted of a form-matched suppressor module fitted to the front. This gun fired standard form ammunition (9x18mm Makarov) which may have had a reduced powder charge. The latter lowered its effective range, accuracy and lethality, but would also significantly lower noise. However, it was long and bulky. The Soviets soldiered on.
They came up with a radical departure - rather than silencing the gun, silence the ammunition. Since they had a state behind them, specifying a whole custom ammunition round wasn't a problem, as the resources to manufacture it were available. They began to experiment with piston-driven ammunition. This looks like a regular cartridge, perhaps a bit bigger - pistols used cartrdiges that were equivalent to or larger than regular rifle cartridges. One reason was that the bullet was almost entirely sunk into the casing. The other was that the casing had to be quite strong.
Although they were ignited by primer, and used conventional powder, set in a cartridge case, there the similarities stopped. The expanding gases of the charge never touched the bullet. Instead, they pushed on a piston set in the case. That piston moved forward and propelled the bullet out of the cartridge and into the rifled barrel of the pistol, and on to its destiny. The clever bit was this - the cartridge case has a shoulder at the front, and while the bullet is narrow enough to pass through, the piston is not. So when the round fires, the piston moves forward, accelerating the bullet, and then slams into the shoulder and stops. This means that almost none of the propellant gases make it out of the cartridge casing before they are sealed into it by the piston, and thus perform the same task as an external supprressor - preventing gas escape - but much more effectively.
There were a few silenced pistols which used single-shot barrels - loaded and operated like Derringers, they were small and inconspicuous, exactly what the doctor ordered for spies and secret police. On the negative side, they only held one or two rounds, and reloading them was time consuming and obvious.
The PSS (finally!) is the culmination of that line of engineering. The PPS is a semiautomatic (autoloading) pistol, using a variant of the blowback mechanism - a variant because no gases escape to provide motive force, it's just pressure on the base of the cartridge from the piston. Since it does not allow gas to escape, many of the disadvantages of that action are mitigated. In addition, it uses lower energy rounds both to maintain low noise and because the strength of the cartridge is a limiting factor - unlike a conventional pistol, the cartridge 'brass' must indefinitely contain the full pressure of the fired charge. These rounds are designated 'SP-4'.
PSS stands for, I believe, Специальный самозарядный пистолет or Pistolet Samozaryadnyy Spetsial'nyy if the internet is to be believed. This translates, according to a Russian I asked, into 'Special Self-loading Pistol' - an incredibly generic and bland name that fits well with its secret agent life.
The advantages of the PSS are all those of the earlier guns, plus the fact that this pistol is semi-automatic and fires from a 6-round box magazine. It seems to be effective out to 20 meters or so, penetrating light protective gear at that range with reasonable accuracy. Tests on the gun performed 'somewhere in Southwest Asia' have indicated (again, if the internet can be believed) that the sound levels produced by firing a PSS are around 122-124 dB, which is very quiet and is around the same noise level as an air rifle. The mechanical design of the gun includes measures taken to slow the slide at the end of its travel, to minimize the noise of its impact against the slide stops.
So on the face of it, this is a handy pocket spy gun. There are are couple of disadvantages, however. Probably the biggest one is this: if the whole point is to leave no sign you were there, and not sign your work, it's not a great idea - because like any semi pistol, it ejects its cartridges. In this case, it will eject something that is absolutely indicative of what kind of weapon did the shooting, and since very few of these pistols exist outside former Eastern Bloc nations, well. Also, the shells it does eject are fairly dangerous, at least for several days - because they are pressurized to the full pressure of the fired gunpowder. It will take a few days for this gas pressure to leak out around the piston and primer, so picking them up to take with you is also not entirely risk-free. Some of these risks are addressed by another gun that uses the SP-4 round - the (very recently produced) OTs-38 Stechkin silent revolver. Although less handy to reload, this deals with the problems of ejecting shells, and doesn't suffer from the usual cylinder gap that makes revolvers normally impossible to suppress effectively.
In any case, the PSS was a Soviet/Russian paramilitary pistol. I'm not sure who manufactured it or even if it was manufactured in a single place, although again the Internet claims a typically Soviet-named design bureau. Ammunition seems to have been available in 12-round boxes, 20 to the spam can and two of those to a crate - much like most Soviet-block ammunition.
Oh, if you're considering trying to collect one or even its ammo here in the United States - be advised that the ATF considers each cartridge to be a suppressor for legal purposes!