What should be configuration of Server for 700 employees?

Actually you need the following:

- A data center equipped with a servers farm consists of domain controller, backup domain controller, exchange server, file and printing server etc.

- A LAN network consists of high performance core switch with distributed switches to server the clients and the departments (end user).

- A WAN Router to connect to the internet with the required security firewalls and appliances, like CISCO ISE and CISCO Ironport web and mail filter.

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The basic requirements should be kept in focus to create server(s). Rest depends on the needs of an organization.

You should use Load Balancing on the servers  so it will increase the efficiency  and protect your down time as a fail over.

This depends on what server you are planning. If it is a web server you are plannng, go for a quad core processor, with a 1TB raid 1 hard disk, so that you will get 500GB of usable space. If that is also meant to act as a file server, go for higher storage, SSD drives and hexa core/ octa core processor. Please keep in mind, the higher the traffic, the higher the bandwidth you may need. So look for nic supported speed before selecting the server. Hope this reply helped

It Depend on what you already have in your Infrastructure.

for example you need Domain controller as a start, & you need application servers depend on your company needs, mail server...etc.