I think every Project Manager knows how easily you can become flooded with the tasks. While developers can afford spending some time on the single task, PM has to switch between a lot of tasks during the single hour (some PMs think that they are multitasking, but it is not true :). Sometimes, in the end of the day I feel like I spent all my time on switching and dream about getting some task on which I can spend 3 hours in a row and not been distracted.
Developers usually say that while they work they fully wrap their mind around the task at hand, they create the “mental model” of the classes, methods, etc and they need some time to “get context loaded” when they start working with the task. They feel something like the “work stream”, so when they are distracted – it takes time to get back to it.
I should say, for me PMs work process is the same – I get to the office in the morning, sit in my chair and have so spend some time to “load mental model” of my projects: project details, people, relationships, todos, etc. Sometimes I do that on my way to work. I am not keeping all details in my head all the time – I unwrap this model when it is needed. The difference between the “work stream” of developer and the manager is that manager’s constants of “interruptions” – you have to think quick, make some decisions, answer questions and be always alarmed.