What was the Ulam?
Radak: The Mishnah calls it a Beis Sha'ar 1 .
Gra: It was two walls in front of Pesach ha'Heichal. They did there matters needed for the Heichal; it would not be honorable to do them in the Heichal.
This is a room outside the Chatzer or house (Perush ha'Mishnayos Ohalos 8:9).
Where was the Ulam?
Rashi: It was in front of the Heichal, at its entrance.
What is the meaning of "Al Pnei Heichal ha'Bayis"?
Malbim: The Ulam was in the east, where the Heichal was, and not in the west (where the Kodesh ha'Kodoshim was).
What is the meaning of "Archo Al Pnei Rochav ha'Bayis"?
Rashi: The length of the Ulam was along the width of the Heichal, from north to south. The longer Midah is called the length, and the shorter is called the width. For the Heichal, from east to west was longer, so it is called the length. For the Ulam, from north to south was longer, so it is called the length, and from east to west is called the width.
What is the meaning of "Al Pnei ha'Bayis"?
Rashi: In front of the Bayis, from the east to outside.
Radak: The Ulam was not distanced from the Bayis (Heichal)
Malbim: Its length was [20 Amos,] like the width of the Heichal. Together, the Bayis and Ulam were 70 long.