Managed & Unmanaged Package

A package is a container for something as small as an individual component or as large as a set of related apps.
After creating a package, you can distribute it to other Salesforce users and organizations, including those outside your company.
Packages come in two forms—
                                                 a. Unmanaged Package
                                                 b. Managed Package
A.     Unmanaged packages are typically used to distribute open-source projects or application                     templates to provide developers with the basic building blocks for an application.
B.      Managed packages are typically used by salesforce.com partners to distribute and sell                          applications to customers

1. Unmanaged  packages are not upgradeable but manage package are upgradeable
2. Unmanaged package is open source (free) but managed package is not open source you have to buy.
3. Everyone can edit unmanaged package but manage package can't  be edit.
4.  In Developer edition  we have the permission to create only unmanaged package but for creating          managed package we have to change the  developer setting.
5. If you are not creating a manage package for distribution  then  registering a namespace prefix is        not required.Because if in your manage package you create a component with name abc and other     org also have the component with same name abc then there will be a conflict arise therefore               removing this conflict we use namespace .

• Apex class source code is completely hidden; unless the Apex class is a global class in which case the global method signatures and variables are exposed.
• The source of Visualforce pages is not hidden. However, the source cannot be edited.
• The source of Visualforce Components is hidden.
• Trigger source code is also hidden.

6.A namespace prefix:
                                    It is a collection of related element ( class,page,object,components,interface..)
                                  a. Distinguishes your package and its contents from those of other developers.
                                  b. Is unique across all salesforce.com organizations.
                                  c. Ensures your exclusive control of all package components.
                                  d. Automatically prepends to all components (custom objects, fields, and                                                  others).Never changes.
                                  e. You are only allowed one managed package in this salesforce.com                                                          organization.


Q- How to create managed package in salesforce org?
A- If you want to create manage package then you have to  follow these steps
   1. Go to setup -- click on quick find the type there package --
   2. Then in Developer setting panel click on edit
   3. Then review the selections and click on continue
   4. Then enter the namespace you want to register and check the availability
   5. Then choose the unmanaged package which you want to convert to manage
   6. Then click on Review  my selection
   7. Then save.

Note:    <apex,aura are the example of namespace >

Domain
Developer edition     : https://customDomainName-dev-ed.my.salesforce.com/
Sandbox                   : https://customDomainName-sandboxName.serverInstance.my.salesforce.com
Production                :  https://customDomainName.mysalesforce.com

Note:
        a. There is only one domain we can create in organisation
        b. Once it is created we can not de-activated or modified
        c. Domain is must for running Lightning  component

Advantage of custom domain
a. We can customise the login page.
b. We can customise login settings ( like login from facebook , twitter, linkedin ,sso)
c. We can work with multiple org with same browser

Q- From where we can find the server instance
A-
     1.From domain URL
     2. From company profile-- company information