Ahead of today's opening free practice session, the air temperature is 22 degrees C, while the track temperature is 24 degrees. It is bright and sunny.

Following last week's test at Mugello, most of the teams have brought updates here, some more than others. Indeed, McLaren, other than a revised (higher) nose, has also made changes to its pit crew following mistakes in the previous couple of races.

One team playing down the updates is Ferrari which insists that while it has brought a few new bits, mainly aerodynamic, the car is not significantly different and definitely not a B-spec chassis.

A number of reserve drivers are on duty this morning, including Bianchi, who replaces di Resta at Force India, Bottas (Senna - Williams), Rossi (Kovalainen - Caterham) and Clos (Karthikeyan - HRT).

First out is Kobayashi, followed by Clos and, a few moments later Petrov, Webber and Pic.

For the first time this year there are two steps between the tyre compounds on offer, these being hard (prime) and soft (option).

One by one the pour onto the track, Button among the early risers.

The Toro Rosso of Vergne is sporting an inordinate amount of flow-viz paint around its hind quarters. As ever, for most teams, Friday is all about testing.

Hamilton is the first driver to complete two installation laps indeed, the McLaren driver looks set to begin a third before diving into the pits at the last possible moment. Both McLarens are sporting the new (high) nose though the old nose is available - however, this is the drivers' first on-track experience of the update since neither was on duty at Mugello.

With 1:16.00 on the clock everyone bar Vettel has been out.

Glock is the first driver to emerge for a second run, the Marussia driver soon joined by de la Rosa and Button.

Ferrari admits that the best birthday present for Stefano Domenicali - who is 47 today - would be a "faster car". Meanwhile the back end of Alonso's is covered in flow-viz paint, absolutely covered.

Glock posts 1:45.783 but moments later teammate Pic paints a far more sensible 31.011.

Vergne goes quickest (27.125) and Kobayashi second (27.157) as the Mercedes crew work on the rear of Schumacher's car. Vergne goes quickest in all three sectors, crossing the line at 25.620.

Hamilton is in the pitlane with Sam Michael and a couple of other crew members discussing a revised (pit) light system.

Thirty-three minutes into the session, Kobayashi goes quickest with a 25.297. Hulkenberg is third ahead of Ricciardo, Raikkonen and Pic.

Despite a lock-up that sees him run wide, Raikkonen goes third with a 25.717, the Lotus looking better with each race that passes.

Almost unseen, Vettel has been out for his installation lap - better late than never.

Raikkonen pits to be fitted with a new nose which the team hopes will be a "little bit different". Elsewhere, Perez tries some cross country running.

Schumacher goes fourth (25.441) and immediately goes quickest in the opening sector of his next lap. Elsewhere, teammate Rosberg goes fourteenth (30.338).

As Schumacher improves to second with a 25.187, Bottas posts a 25.428 to go fifth. Next time around the Finn goes second (25.120), closing to within 0.208s of pace-setter Kobayashi.

At half-time, it's: Kobayashi, Bottas, Schumacher, Raikkonen, Vergne, Massa, Webber, Rosberg, Hulkenberg and Perez. All times on the prime tyre thus far.

De la Rosa is on track with a new rear wing, HRT not having attended last week's test at Mugello, instead playing host to Jean Todt at its new factory. Moments later the cameras pick up a small piece of bargeboard falling from the Spaniard's car at the end of the main straight.

Vettel pops up in fifth, the German posting a 25.324. On his subsequent lap he goes quickest with a 24.808 having been quickest overall in S3.